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Interfacing

Peripherals to

Computer System

Conceived By-

Shubham Pandey

Department of Electronics Engineering

A.I.E.T

Lucknow, Uttar Pradesh

India

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Disclaimer

The work followed is original editing of mine (but

the information has been referred through many

internet sources) and has been conceived as the part

of the seminar report submitted to the institution.

This is to therefore kindly inform the viewers that

any information in this report should not be trusted

blindly and thus I am not responsible for any ill

consequences arising due to this.

Shubham Pandey

Azad Institute of Engineering and Technology

Lucknow, Uttar Pradesh, India

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Disk Interface Technology

The demand for storage to be available anytime, anywhere is driving the

development of a new mix of disk interface technologies. This guide provides a basic comparison

of existing and emerging technologies to help sort through the options that are available today and

in the future. A comparative matrix of key features follows.

Parallel Advanced Technology Attachments (ATA)

Parallel ATA, commonly referred to as simply ―ATA‖, is an industry

specification that evolved from the original Advanced Technology disk-interface. The ATA

standard, first developed in 1984 defines a command and register set for the interface between the

disk drive and the PC. Today’s ATA-133 interface delivers a maximum data transfer rate of 133

MB/sec and supports two parallel ports, with each port supporting two internal hard drives. ATA

is currently the standard hard disk drive interconnect in desktop PCs and is implemented in many

Direct Attached Storage (DAS) and Network Attached Storage (NAS) systems.

Parallel Small Computer System Interface (SCSI)

Parallel SCSI, better known as ―SCSI‖, is a shared bus technology that

connects various internal and external devices to a PC or server. SCSI technology allows for

connectivity of up to 15 devices, and Ultra320 SCSI supports a data transfer rate of up to 320

MB/sec. First approved as a standard in 1986, SCSI technology has evolved to be the most widely

used interface in workstations, as well as in servers and networked storage systems today.

Fiber Channel (FC)

Fiber Channel serves two purposes. It is both a high-speed switched fabric

technology, and a disk interface technology. It supports a maximum data transfer rate of 400

MB/sec (full duplex; or half duplex, dual loop configuration) over 30 meters of copper cable or 10

kilometers over single-mode fiber optic links. When implemented in a continuous arbitrated loop

(FC-AL), Fiber Channel can support up to 127 individual storage devices and host systems without

a switch. Disk arrays and backup devices directly attach to the loop rather than onto any one server.

FC was first approved as a standard in 1994 and is primarily implemented in high-end SAN

systems.

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Serial Advanced Technology Attachments 1.0 (SATA)

Developed in 2001, SATA is the first generation of the new disk interface

technology replacing Parallel ATA. In desktops, SATA is expected to replace Parallel ATA as the

primary internal storage for PCs. SATA 1.0 delivers a maximum data transfer rate of 1.5 GB/sec

(1500 MB/sec) per port and its future roadmap shows growth to 6.0 GB/sec (6000 MB/sec).

Advantages of SATA include a point-to-point interconnect that enables full bandwidth available to

each device, lower pin-count, lower voltage, hot-plug capability, thin cabling, longer cable length

and register-level compatibility with Parallel ATA. These added features make SATA an option for

DAS, NAS and some Storage Area Network (SAN) systems where Parallel ATA may not have

been considered.

Serial Advanced Technology Attachments II (SATA II)

SATA II is the second-generation SATA disk interface technology currently under

development by the SATA working group. The SATA II specification picks up where SATA 1.0

left off, and will be deployed in 2 phases. The first phase, called ―Extensions to Serial ATA 1.0‖,

focuses primarily on addressing the needs of servers and networked storage. These include

queuing, enclosure services, hot plug, cold presence detect, cabling and backplane improvements.

The second phase is anticipated to scale performance to 3.0 GB/sec (3000 MB/sec) per port. These

combined enhancements will make SATA II a good option for DAS, NAS and SAN storage

systems where price/performance and cost are key factors.

Serial Attached Small Computer System Interface (SAS)

Serial Attached SCSI (SAS) is under development by the T10 standards committee.

This committee is addressing the future limitations of the parallel SCSI interface, principally the

bandwidth scaling limitations inherent in a parallel interface. SAS will deliver a maximum data

transfer of 3.0 GB/sec (3000 MB/sec) per device, and it can support up to 128 devices via an

expander. One of the key features of SAS is its anticipated ability to allow users to connect either a

SATA or a SAS hard disk drive in an enclosure with expander capabilities. Its point-to-point

configuration and highly scalable architecture makes SAS a good option for mid-range to high-end

DAS, NAS and SAN storage systems.

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ATA SCSI Fiber

Channel

SATA SATA II Serial

Attached

SCSI Performance Technology

Introduction

(Year)

2000

2002

2001 2002

2003

2004

Maximum

Bus Speed

100 MB/s

shared per

channel

320 MB/s

Shared per

channel

4 GB/s

dedicated

or shared

1.5GB/sec

dedicated

per device

3 GB/sec

dedicated

per device

3 GB/sec

dedicated

per device

Topology Shared bus

master/slave

Shared bus Arbitrated

loop/

switched

fabric

Point-to-

point

Point-to-

point

Point-to-

point

Number of

Device

/Channel

2 15 127/

arbitrated

loop

1

(expandable

to 128)

1

(expandable

to 128)

1

(expandable

to 128)

Command

Queuing

No Yes Yes Yes Yes Yes

Primary Applications Device

Placement

Internal Internal

/External

External Internal Internal

/External

Internal

/External

Hard Disk

Drive(HDD)

Classes

Desktop Enterprise Enterprise Desktop

with some

Enterprise

features

Desktop

with some

Enterprise

features

Enterprise

Devices

other than

HDDs

Many Many Few Many Many Few

Characteristics

Internal

cable width

2 inches 1.75 inches 0.156

inches

0.312

inches

0.312

inches

0.312

inches

Number of

cable pins

40

(+40

conductors)

68 or 80 4 22 (7

signal)

22 (7

signal)

22 (7

signal)

Maximum

Cable

length

18 inches 12 metres 10 Kms 1 metres 6 metres 10 metres

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Parallel Advanced Technology Attachments (PATA)

ATA/ATAPI is an evolution of the AT Attachment Interface, which was itself

evolved in several stages from Western Digital's original Integrated Drive Electronics (IDE)

interface. Parallel ATA (PATA) is an interface standard for the connection of storage devices such

as hard disks, solid-state drives, and CD-ROM drives in computers. The standard is maintained by

X3/INCITS committee. It uses the underlying AT Attachment and AT Attachment Packet Interface

(ATA/ATAPI) standards. Parallel ATA only allows cable lengths up to 18 in (460 mm). Because of

this length limit the technology normally appears as an internal computer storage interface. The

name of the standard was originally conceived as "PC/AT Attachment" as its primary feature was a

direct connection to the 16-bit ISA bus introduced with the IBM PC/AT. The name was shortened

to "AT Attachment" to avoid possible trademark issues. It is not spelled out as "Advanced

Technology" anywhere in current or recent versions of the specification; it is simply "AT

Attachment".

IDE and ATA-1

The term Integrated Drive Electronics (IDE) refers not just to the connector and interface

definition, but also to the fact that the drive controller is integrated into the drive, as opposed to a

separate controller on or connected to the motherboard. The integrated controller presented the

drive to the host computer as an array of 512-byte blocks with a relatively simple command

interface. This relieved the software in the host computer of the chores of stepping the disk head

arm, moving the head arm in and out, and so on, as had to be done with earlier ST-506 and ESDI

hard drives. All of these low-level details of the mechanical operation of the drive were now

handled by the controller on the drive itself. This also eliminated the need to design a single

controller that could handle many different types of drives, since the controller could be unique for

the drive. The host need only ask for a particular sector, or block, to be read or written, and either

accept the data from the drive or send the data to it.

The second ATA interface

Originally, there was only one ATA controller in early PCs, which could support up to two

hard drives. At the time in combination with the floppy drive, this was sufficient for most people,

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and eventually it became common to have two hard drives installed. When the CDROM was

developed, many computers were unable to accept them due to already having two hard drives

installed. Adding the CDROM would have required removal of one of the drives. Although SCSI

was available as a CDROM expansion option at the time, but devices with SCSI were more

expensive than ATA devices due to the need for a smart controller that is capable of bus arbitration.

SCSI typically added US$ 100-300 to the cost of a storage device, in addition to the cost of a SCSI

controller. The less-expensive solution was the addition of the second ATA interface, typically

included as an expansion option on a sound card. It was included on the sound card because early

business PCs did not include support for more than simple beeps from the internal speaker, and

tuneful sound playback was considered unnecessary for early business software. ATA ruled as the

primary storage device interface and in some systems a third and fourth motherboard interface was

provided for up to eight ATA devices attached to the motherboard. Enhanced IDE (EIDE)

included most of the features of the forthcoming ATA-2 specification and several additional

enhancements. Other manufacturers introduced their own variations of ATA-1 such as "Fast ATA"

and "Fast ATA-2". ATA-2 also was the first to note that devices other than hard drives could be

attached to the interface.

AT Attachments Packet Interface (ATAPI)

The introduction of ATAPI (ATA Packet Interface) by a group called the Small Form

Factor committee allowed ATA to be used for a variety of other devices that require functions

beyond those necessary for hard disks. ATAPI devices include CD-ROM and DVD-ROM drives,

tape drives, and large-capacity floppy drives such as the Zip drive and Super Disk drive. ATAPI is

actually a protocol allowing the ATA interface to carry SCSI commands and responses; therefore

all ATAPI devices are actually "speaking SCSI" other than at the electrical interface. In fact, some

early ATAPI devices were simply SCSI devices with an ATA/ATAPI to SCSI protocol converter

added on. The SCSI commands and responses are embedded in "packets" (hence "ATA Packet

Interface") for transmission on the ATA cable. This allows any device class for which a SCSI

command set has been defined to be interfaced via ATA/ATAPI.

Drive size limitations

The original ATA specification used a 28-bit addressing mode, allowing for the addressing

of 228

sectors of 512 bytes each, resulting in a maximum capacity of about 137 GB. The BIOS in

early PCs imposed smaller limits such as 8.46 GB, with a maximum of 1024 cylinders, 256 heads

and 63 sectors, but this was not a limit imposed by the ATA interface. ATA-6 introduced 48-bit

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addressing, increasing the limit to 144 Petabytes. As a consequence, any ATA drive of capacity

larger than 137 gigabytes must be an ATA-6 or later drive. Connecting such a drive to a host with

an ATA-5 or earlier interface will limit the usable capacity to the maximum of the controller.

Parallel ATA interface

Parallel ATA cables transfer data 16 bits at a time. ATA's ribbon cables have had 40 wires

for most of its history (44 conductors for the smaller form-factor version used for 2.5" drives), but

an 80 wire version appeared with the introduction of the Ultra DMA/33 (UDMA) mode. All of the

additional wires in the new cable are ground wires, interleaved with the previously defined wires to

reduce the effects of capacitive coupling between neighboring signal wires, reducing crosstalk.

Capacitive coupling is more of a problem at higher transfer rates, and this change was necessary to

enable the 66 MB/s transfer rate of UDMA4 to work reliably. The faster UDMA5 and UDMA6

modes also require 80-conductor cables.

Connector Assignments and Color Coding: For the first time, the 80-conductor cable defines

specific roles for each of the connectors on the cable; the older cable did not. Color coding of the

connectors is used to make it easier to determine which connector goes with each device:

Blue: The blue connector attaches to the host (motherboard or controller).

Gray: The gray connector is in the middle of the cable, and goes to any slave (device 1)

drive if present on the channel.

Black: The black connector is at the opposite end from the host connector and goes to the

master drive (device 0), or a single drive if only one is used.

(PATA connector cable side)

Pin Signal Description

1 /RESET Reset

2 GND Ground

3 DD7 Data 7

4 DD8 Data 8

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(Comparison between the size of 40 conductor cable)

(40 conductor PATA Cable)

Multiple devices on a cable

If two devices attach to a single cable, one

must be designated as device 0 (commonly

referred to as master) and the other as device 1

(slave). This distinction is necessary to allow both

drives to share the cable without conflict. The

master drive is the drive that usually appears

"first" to the computer's BIOS and/or operating

system. The mode that a drive must use is often set

by a jumper setting on the drive itself, which must be manually set to master or slave. If there is a

single device on a cable, it should be configured as master

Cable Select

5 DD6 Data 6

6 DD9 Data 9

7 DD5 Data 5

8 DD10 Data 10

9 DD4 Data 4

10 DD11 Data 11

11 DD3 Data 3

12 DD12 Data 12

13 DD2 Data 2

14 DD13 Data 13

15 DD1 Data 1

16 DD14 Data 14

17 DD0 Data 0

18 DD15 Data 15

19 GND Ground

20 KEY Key

21 n/c Not connected

22 GND Ground

23 /IOW Write Strobe

24 GND Ground

25 /IOR Read Strobe

26 GND Ground

27 IO_CH_RDY I/O channel ready

28 ALE Address Latch Enable

29 n/c Not connected

30 GND Ground

31 IRQR Interrupt Request

32 /IOCS16 IO Chip Select 16

33 DA1 Address 1

34 n/c Not connected

35 DA0 Address 0

36 DA2 Address 2

37 /IDE_CS0 (1F0-1F7)

38 /IDE_CS1 (3F6-3F7)

39 /ACTIVE Led driver

40 GND Ground

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Cable select is controlled by pin 28. The host adapter grounds this pin; if a device sees that the pin

is grounded, it becomes the master device; if it sees that pin 28 is open, the device becomes the

slave device. This setting is usually chosen by a jumper setting on the drive called "cable select",

usually marked CS, which is separate from the "master" or "slave" setting. Note that if two drives

are configured as master and slave manually, this configuration does not need to correspond to their

position on the cable. Pin 28 is only used to let the drives know their position on the cable; it is not

used by the host when communicating with the drives.

With the 40-wire cable it was very common to implement cable select by simply cutting the pin 28

wire between the two device connectors; putting the slave device at the end of the cable, and the

master on the middle connector. If there is just one device on the cable, this results in an unused

stub of cable, which is undesirable for physical convenience and electrical reasons. The stub causes

signal reflections, particularly at higher transfer rates.

Starting with the 80-wire cable defined for use in ATAPI5/UDMA4, the master device goes at the

end of the 18-inch (460 mm) cable--the black connector--and the slave device goes on the middle

connector--the gray one--and the blue connector goes onto the motherboard. So, if there is only one

(master) device on the cable, there is no cable stub to cause reflections.

Two devices on one cable — speed impact

It is a common misconception that, if two devices of different speed capabilities are on the same

cable, both devices' data transfers will be constrained to the speed of the slower device. For all

modern ATA host adapters this is not true, as modern ATA host adapters support independent

device timing. This allows each device on the cable to transfer data at its own best speed.

Only one device on a cable can perform a read or write operation at one time, therefore a fast

device on the same cable as a slow device under heavy use will find it has to wait for the slow

device to complete its task first. However, most modern devices will report write operations as

complete once the data is stored in its onboard cache memory, before the data is written to the

(slow) magnetic storage. This allows commands to be sent to the other device on the cable,

reducing the impact of the "one operation at a time" limit.

Parallel AT version details and features

ATA-1 (IDE), 8.3MBytes/sec, 8 or 16 bit data width, 40 pin data ribbon cable/connector.

With a maximum of 2 devices on the bus. Using PIO Modes 0, 1 or 2. Performed no bus

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error correction. The ATA-1 specification was released in 1994, and was withdrawn in

1999.

ATA-2 (EIDE, or Fast ATA), 16.6MBytes/sec, 8 or 16 bit data width, 40 pin data ribbon

cable/connector. With a maximum of 4 devices on the bus. Using PIO Modes 0, 1, 2, 3, or

4. The ATA-2 specification was released in 1995 and was withdrawn in 2001.

ATA-3, 16MBytes/sec, 16 bit data width, 40 pin data ribbon cable/connector. Using PIO

Modes 0, 1, 2, 3, or 4 and Multiword DMA modes 1 and 2. Runs with 120nS Strobes (rising

edge to rising edge). Includes CRC. ATAPI (ATA Packet Interface) is the CD-ROM side of

the interface. It uses the same connector as ATA, and adds 1 for analog and 1 for digital

audio. The ATA-3 specification was released in 1997 and was withdrawn in 2002.

ATA-4 Ultra-ATA/33, 33MBytes/sec, 16 bit data width, 40 pin data ribbon cable/connector.

Using PIO Modes 0, 1, 2, 3, or 4 and Multiword DMA modes 1 and 2 and Ultra DMA

modes 0, 1, and 2. Runs with 120 nS strobes (rising edge to rising edge), but used both

edges of the Strobe producing an effective 60nS Strobe rate. 33MBps Transfer speed =

[(1/120nS) x 2 bytes x 2]. Where 120nS cycle time is 4 clock periods at 30nS each. Added

CRC checking. The ATA-4 standard was released in 1998.

ATA-5 Ultra-ATA/66, 66MBytes/sec, 16 bit data width 40 pin data connector/80 pin cable,

with the additional 40 new pins being Ground. The new cable allows ATA/66 to run at a

faster rate then ATA/33. Using PIO Modes 0, 1, 2, 3, or 4 and Multiword DMA modes 1

and 2 and Ultra DMA modes 0, 1, 2, 3 and 4. Runs with 60nS Strobes (rising edge to rising

edge), but uses both edges of the Strobe producing an effective 30nS Strobe rate. 66MBps

Transfer speed = [(1/60nS) x 2 bytes x 2]. Where 60nS cycle time is 2 clock periods at 30nS

each. The ATA-5 standard was released in 2000.

ATA-6 Ultra-ATA/100, 100MBytes/sec,16 bit data width 40 pin data connector/80 pin

cable, with the additional 40 new pins being Ground. Using PIO Modes 0, 1, 2, 3, or 4 and

Multiword DMA modes 1 and 2 and Ultra DMA modes 0, 1, 2, 3, 4 and 5. 100MBps

Transfer speed = [(1/40nS) x 2 bytes x 2]. Where 40nS cycle time is 2 clock periods at 20nS

each. The ATA-6 standard was released in 2002.

ATA-7 Ultra-ATA/133, 133MBytes/sec,16 bit data width 40 pin data connector/80 pin

cable, with the additional 40 new pins being Ground. Using PIO Modes 0, 1, 2, 3, or 4 and

Multiword DMA modes 0, 1 and 2 and Ultra DMA modes 0, 1, 2, 3, 4, 5 and 6. 133MBps

Transfer speed = [(1/30nS) x 2 bytes x 2]. Where 30nS cycle time is 2 clock periods at 15nS

each. The ATA-7 standard was released in 2005. With the introduction of Serial ATA, this

is the last expected update of the IDE [PATA] bus. SATA is faster, and requires a smaller

cable, which means better air flow in the case.

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Parallel Small Computer System Interface

SCSI is a set of standards for physically connecting and transferring data between

computers and peripheral devices. The SCSI standards define commands, protocols, and electrical

and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it can

connect a wide range of other devices, including scanners and CD drives. The SCSI standard

defines command sets for specific peripheral device types; the presence of "unknown" as one of

these types means that in theory it can be used as an interface to almost any device, but the standard

is highly pragmatic and addressed toward commercial requirements.

SCSI is an intelligent interface: it hides the complexity of physical format. Every device

attaches to the SCSI bus in a similar manner.

SCSI is a peripheral interface: up to 8 or 16 devices can be attached to a single bus. There

can be any number of hosts and peripheral devices but there should be at least one host.

SCSI is a buffered interface: it uses hand shake signals between devices, SCSI-1, SCSI-2

have the option of parity error checking. Starting with SCSI-U160 (part of SCSI-3) all

commands and data are error checked by a CRC32 checksum.

SCSI is a peer to peer interface: the SCSI protocol defines communication from host to host, host to

a peripheral device, peripheral device to a peripheral device. However most peripheral devices are

exclusively SCSI targets, incapable of acting as SCSI initiators unable to initiate SCSI transactions

themselves. Therefore peripheral-to-peripheral communications are uncommon, but possible in

most SCSI applications.

An overview

SCSI Type Speed

(MBps)

Bus

Width

Pins ID's

Connector

SCSI-1 1 to 5 8 25 or 50 8

Sub-D25, Amphenol 50,

Sub-D50

SCSI-2 5 to 10 8 50 8 Micro-D50

SCSI-2

fast/wide

up to 40 16 50 8

Micro-D50

SCSI-3 16 68 32 Micro-D68

SCSI-3

fast/wide

32 68 32

Micro-D68

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The SCSI interface is a parallel interface the communication between devices is done by initiators

and targets. An initiator is a device which requests something from a target. The initiator is most

commonly a host-adapter in a computer. The target is the one that takes the job and carries it out.

Because of the definition of SCSI that a job is given by a initiator and then carried out by a target

without the initiator knowing how the target is doing it and even not knowing when the job is done

the roles of initiator and target may switch. As soon as the target is done with its job it initiates the

host, which will become target. The purpose of all this is that as soon as the target knows what the

initiator wants the bus will become free for other jobs to be send to other targets. The bus is used

more economically. Instead of a computer waiting for data coming from a scanner, the bus can be

used by the computer to read data from the hard disk. SCSI has the capability to connect more than

two devices to a bus. These devices may be targets or initiators. So it is possible for two hosts to

share one tape streamer, but it is also possible for one host to have access to several hard disks. The

identification of the devices is done by an ID. SCSI-1 and SCSI-2 have a maximum of 8 ID's and

SCSI-3 has even 32 possible ID's. There is no such thing as plain SCSI. There is SCSI-1, -2 and -3

and together with this there is Differential and Single-ended, and for the termination there is

passive and active. Single-ended means that there is a ground and a signal wire. Much like in

RS232. Differential on the other hand has no ground wire, but all signals have two wires, a positive

and a negative one and the voltage difference between them carries the information (1 or 0). Much

like RS422. To make everything more complex the SCSI bus must be terminated to work properly.

In SCSI there is active termination, which means the termination is done by a voltage regulator and

some resistors. This is for the Single-Ended interface. With differential SCSI live is easier. There is

only passive termination which means a resistor is placed at the end and at the beginning of the

cable. But it's not the same termination as for passive single-ended SCSI. And finally there is the

difference between SCSI-3 and SCSI-2 wide. Both have 16 bytes transmissions, but SCSI-2 has

only 50 wires and SCSI-3 has 68, so why take a, more expensive cable? The reason is that SCSI-2

has a 50 wire cable and only 8 data lines there will be a low and high byte transmission. Each 16 bit

word is split in a low and a high byte. These are transmitted one after the other and thus taking

twice as long as 16 bit SCSI-3. This makes SCSI-3 faster and more economic.

There are a dozen SCSI interface names, most with ambiguous wording (like Fast SCSI, Fast Wide

SCSI, Ultra SCSI, and Ultra Wide SCSI); three SCSI standards, each of which has a collection of

modular, optional features; several different connector types; and three different types of voltage

signaling. The leading SCSI card manufacturer, Adaptec, has manufactured over 100 varieties of

SCSI cards over the years. In actual practice, many experienced technicians simply refer to SCSI

devices by their bus bandwidth (i.e. SCSI 320 or SCSI 160) in Megabytes per second.

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SCSI-1 features an 8-bit parallel bus (with parity), running asynchronously at 3.5 MB/s or 5 MB/s

in synchronous mode, and a maximum bus cable length of 6 meters. A rarely seen variation on the

original standard included a high-voltage differential (HVD) implementation whose maximum

cable length was 25 meters.

SCSI-2 standard was introduced in 1994 and gave rise to the Fast SCSI and Wide SCSI variants.

Fast SCSI doubled the maximum transfer rate to 10 MB/s and Wide SCSI doubled the bus width to

16 bits on top of that to reach a maximum transfer rate of 20 MB/s.

Ultra-2 SCSI was introduced in 1997 and featured a low-voltage differential (LVD) bus. For this

reason ultra-2 is sometimes referred to as LVD SCSI. LVD's greater resistance to noise allowed a

maximum bus cable length of 12 meters. At the same time, the data transfer rate was increased to

80 MB/s. Ultra-2 SCSI actually had a relatively short lifespan, as it was soon superseded by Ultra-3

(Ultra-160) SCSI.

Ultra-3 also known as Ultra-160 SCSI and introduced toward the end of 1999, this version was

basically an improvement on the ultra-2 standard, in that the transfer rate was doubled once more to

160 MB/s by the use of double transition clocking. Ultra-160 SCSI offered new features like cyclic

redundancy check (CRC), an error correcting process, and domain validation.

Ultra-320 is the Ultra-160 standard with the data transfer rate doubled to 320 MB/s. The latest

working draft for this standard is revision 10 and is dated May 6, 2002. Nearly all SCSI hard drives

being manufactured at the end of 2003 were Ultra-320 devices.

Ultra-640, otherwise known as Fast-320 was promulgated as a standard (INCITS 367-2003 or SPI-

5) in early 2003. Ultra-640 doubles the interface speed yet again, this time to 640 MB/s. Ultra-640

pushes the limits of LVD signaling; the speed limits cable lengths drastically, making it impractical

for more than one or two devices. Because of this, most manufacturers have skipped over Ultra640

and are developing for Serial Attached SCSI instead.

SCSI IDs

All devices on a parallel SCSI bus must have a SCSI ID. The initiator (adapter or controller) SCSI

ID is usually set by a physical jumper or switch. The target (disk-drive) SCSI IDs are either set by

physical jumpers or by control signals which vary for each connector on an enclosure backplane.

The SCSI ID field widths are:

Bus-width ID width IDs available

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8-bit 3-bit 8

16-bit 4-bit 16

Arbitration

All SCSI commands start with a process called arbitration when one or more devices attempt to

access the bus. During the arbitration phase, the 8 or 16 data bus signals are used to identify which

device(s) are requesting access. All SCSI devices must implement the same arbitration algorithm so

the result is always unanimous. SCSI IDs are used in the arbitration phase to determine which

device next gets access to the SCSI bus. If two devices attempt to access the bus at the same time

then the one with the highest priority SCSI ID will win the arbitration. The priority sequence for an

8-bit wide parallel SCSI bus is quite simple, but the priority sequence for a 16-bit wide parallel

SCSI bus has to meet legacy requirements so is less obvious:

Bus width SCSI ID priority (from highest to lowest)

8-bit 7, 6, 5, 4, 3, 2, 1, 0

16-bit 7, 6, 5, 4, 3, 2, 1, 0, 15, 14, 13, 12, 11, 10, 9, 8

The SCSI ID of the initiator is usually set to the highest priority value of 7. If there are two

initiators then their SCSI IDs are usually set to 7 and 6. All the remaining SCSI IDs can then be

used for disk-drives or other target devices. The arbitration process can use up a lot of bus

bandwidth so more recent devices support a simplified protocol called Quick Arbitration and

Selection (QAS).

Termination

Parallel SCSI buses must always be terminated at both ends to ensure reliable operation. Without

termination, data transitions would reflect back from the ends of the bus causing pulse distortion

and potential data loss. A positive DC termination voltage is provided by one or more devices on

the bus, typically the initiator(s). This positive voltage is called TERMPOWER and is usually

around +4.3 volts. TERMPOWER is normally generated by a diode connection to +5.0 volts. This

is called a diode-OR circuit, designed to prevent backflow of current to the supplying device. A

device that supplies TERMPOWER must be able to provide up to 900 mA (single-ended SCSI) or

600 mA (differential SCSI).

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Termination can be passive or active. Passive termination means that each signal line is

terminated by two resistors, 220 Ω to TERMPOWER and 330 Ω to ground. Active termination

means that there is a small voltage regulator which provides a +3.3 V supply. Each signal line is

then terminated by a 110 Ω resistor to the +3.3 V supply. Active termination provides a better

impedance match than passive termination because most flat ribbon cables have a characteristic

impedance of approximately 110 Ω. Forced perfect (FPT) termination is similar to active

termination, but with added diode clamp circuits which absorb any residual voltage overshoot or

undershoot. There is a special case in SCSI systems that have mixed 8-bit and 16-bit devices where

high-byte termination may be required. In current practice most parallel SCSI buses are LVD and

so require external, active termination. The usual termination circuit consists of a +3.3 V linear

regulator and commercially available SCSI resistor network devices.

Pin configuration of 50 pin SCSI

Pin # Single

Ended

Signal Name

Differential

Signal Name

1 GROUND GROUND

2 GROUND +DB0

3 GROUND +DB1

4 GROUND +DB2

5 GROUND +DB3

6 GROUND +DB4

7 GROUND +DB5

8 GROUND +DB6

9 GROUND +DB7

10 GROUND +PARITY

11 GROUND DIFFSENSE

12 RESERVED RESERVED

13 OPEN TERMPWR

14 RESERVED RESERVED

15 GROUND +ATN

16 GROUND GROUND

17 GROUND +BSY

18 GROUND +ACK

19 GROUND +RST

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Pin configuration of 68 pin SCSI

20 GROUND +MSG

21 GROUND +SEL

22 GROUND +C/D

23 GROUND +REQ

24 GROUND +I/O

25 GROUND GROUND

Pin # Single

Ended

Signal Name

Differential

Signal Name

26 -DB0 GROUND

27 -DB1 -DB0

28 -DB2 -DB1

29 -DB3 -DB2

30 -DB4 -DB3

31 -DB5 -DB4

32 -DB6 -DB5

33 -DB7 -DB6

34 -PARITY -DB7

35 GROUND -PARITY

36 GROUND GROUND

37 RESERVED RESERVED

38 TERMPWR TERMPWR

39 RESERVED RESERVED

40 GROUND -ATN

41 -ATN GROUND

42 GROUND -BSY

43 -BSY -ACK

44 -ACK -RST

45 -RST -MSG

46 -MSG -SEL

47 -SEL -C/D

48 -C/D -REQ

49 -REQ -I/O

50 -I/O GROUND

Pin # Single Ended

Signal Name

Differential

Signal name

1 GROUND +DB12

2 GROUND +DB13

3 GROUND +DB14

4 GROUND +DB15

5 GROUND +PARITY1

6 GROUND GROUND

7 GROUND +DB0

8 GROUND +DB1

9 GROUND +DB2

10 GROUND +DB3

11 GROUND +DB4

12 GROUND +DB5

13 GROUND +DB6

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Fibre Channel

14 GROUND +DB7

15 GROUND +PARITY

16 GROUND DIFFSENSE

17 TERMPWR TERMPWR

18 TERMPWR TERMPWR

19 RESERVED RESERVED

20 GROUND +ATN

21 GROUND GROUND

22 GROUND +BSY

23 GROUND +ACK

24 GROUND +RST

25 GROUND +MSG

26 GROUND +SEL

27 GROUND +C/D

28 GROUND +REQ

29 GROUND +I/O

30 GROUND GROUND

31 GROUND +DB8

32 GROUND +DB9

33 GROUND +DB10

34 GROUND +DB11

Pin # Single Ended

Signal Name

Differential

Signal name

35 -DB12 -DB12

36 -DB13 -DB13

37 -DB14 -DB14

38 -DB15 -DB15

39 -PARITY1 -PARITY1

40 -DB0 GROUND

41 -DB1 -DB0

42 -DB2 -DB1

43 -DB3 -DB2

44 -DB4 -DB3

45 -DB5 -DB4

46 -DB6 -DB5

47 -DB7 -DB6

48 -PARITY -DB7

49 GROUND -PARITY

50 GROUND GROUND

51 TERMPWR TERMPWR

52 TERMPWR TERMPWR

53 RESERVED RESERVED

54 GROUND -ATN

55 -ATN GROUND

56 GROUND -BSY

57 -BSY -ACK

58 -ACK -RST

59 -RST -MSG

60 -MSG -SEL

61 -SEL -C/D

62 -C/D -REQ

63 -REQ -I/O

64 -I/O GROUND

65 -DB8 -DB8

66 -DB9 -DB9

67 -DB10 -DB10

68 -DB11 -DB11

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FC is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is

standardized in the T11 - INCITS. It started use primarily in the supercomputer field, but has

become the standard connection type for SAN in enterprise storage. Despite its name, Fibre

Channel signaling can run on both twisted pair copper wire and fiber-optic cables. Fibre Channel

deploys Fibre Channel Protocol (FCP) which predominantly transports SCSI commands over

Fibre Channel networks.

Fibre Channel topologies

There are three major Fibre Channel topologies, describing how a number of ports are connected

together. A port in Fibre Channel terminology is any entity that actively communicates over the

network, not necessarily a hardware port. This port is usually implemented in a device such as disk

storage, an HBA on a server or a Fibre Channel switch.

1) Point-to-Point (FC-P2P). Two devices are connected back to back. This is the simplest

topology, with limited connectivity.

2) Arbitrated loop (FC-AL). In this design, all devices are in a loop or ring, similar to token

ring networking. Adding or removing a device from the loop causes all activity on the loop

to be interrupted. The failure of one device causes a break in the ring. Fibre Channel hubs

exist to connect multiple devices together and may bypass failed ports. A loop may also be

made by cabling each port to the next in a ring.

A minimal loop containing only two ports, while appearing to be similar to FC-P2P,

differs considerably in terms of the protocol.

Multiple pairs of ports may communicate simultaneously in a loop.

3) Switched fabric (FC-SW). All devices or loops of devices are connected to Fibre Channel

switches, similar conceptually to modern Ethernet implementations. Advantages of this

topology over FC-P2P or FC-AL include:

The switches manage the state of the fabric, providing optimized interconnections.

The traffic between two ports flows through the switches only, it is not transmitted

to any other port.

Failure of a port is isolated and should not affect operation of other ports.

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Optical carrier medium variants

Media Type Speed (MByte/s) Transmitter Distance

Single-Mode Fiber 400 1300 nm Long wave Laser 2 m - 2 km

200 1550 nm Long wave Laser 2 m - >50 km

1300 nm Long wave Laser 2 m - 2 km

100 1550 nm Long wave Laser 2 m - >50 km

1300 nm Long wave Laser 2 m - 10 km

1300 nm Long wave Laser 2 m - 2 km

Multimode Fiber (50µm) 400 850 nm Short wave Laser 0.5 m - 150m

200 0.5 m - 300m

100 0.5 m - 500m

2 m - 175m

Fibre Channel and Networks

Though it has many features of a network, Fibre Channel is less a network than a high speed

switching system that interconnects relatively local devices. With its high bandwidth and ability to

support multiple protocols simultaneously, Fibre Channel enables near-instant access to massive

amounts of data in SANs and other modern computing environments. Collision-based Ethernet

networks are ubiquitous, largely because they allow multiple individual clients to share retrieved

data in a very simple and economical way. Such networks are most successful when supporting

front-end functions. However, they are too inefficient to be used in block-level storage

environments, such as those found in data centers. For throughput, scalability, and attainable

network lengths, Fibre Channel is far superior to Ethernet.

Data throughput With the currently available 2Gb-rated Fibre Channel in the network, data

transfer rates are very close to 200MB/s, as expected. In a Gigabit Ethernet network,

however, collision management claims so much bandwidth that even 1Gb rates are difficult

to achieve consistently.

Scalability. Whether device connections consist of a single point-to-point link or involve

hundreds of integrated, enterprise wide servers, Fibre Channel networks perform with equal

reliability, high rates, and flexible configuration, achieving scalable densities up to

thousands of ports. Although IP-based storage networks theoretically can scale to hundreds

of ports, there is no widespread use to demonstrate this capability.

Network lengths. With Fibre Channel, the switches and cables that carry the data, can be

either copper or optical fibre. Performance is the same, though copper is limited in length to

less than 3 meters. Without the benefit of repeaters, long-haul copper Ethernet networks are

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limited to 100–200 meters, depending on the Ethernet protocol version. Currently, the

maximum theoretical distance for long-haul Fibre Channel networks using fibre-optic links

is 10 Kms.

Deployment Scenarios of FC

Workgroup SAN

Consider this type of deployment when you need to manage many large files and rapidly

growing amounts of data—video and audio editing and storage, for example. The RAID storage

pool allows quick, reliable scaling of storage and backup capabilities. Fibre Channel uniquely

provides in-order delivery of data, necessary for efficient access to media files. In addition to the

Fibre Channel switch, dedicated metadata controllers help mediate traffic for maximum data

transfer rates.

Fibre Channel connector pin configurations

There are various Fibre Channel connectors in use in the computer industry. The following

sections describe the most common Fibre Channel pinouts with some comments about the purpose

of their electrical signals. The most familiar Fibre Channel connectors are cable connectors, used

for interconnects between initiators and targets (usually disk enclosures). There are also "device

connectors" that can be found on Fibre Channel disk-drives and backplanes of enclosures. The

device connectors include pins for power and for setting disk options.

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9-pin "DE-9" cable connector

Optional pins 2, 3, 7, and 8 are intended

for use with an external optical

converter. This is often called a Media

Interface Assembly (MIA). Fibre

channel DE-9 connectors often have

only the 4 required contacts installed.

Note that they are the four outermost

contacts. This is an easy way to tell a fibre channel cable from an RS-232 cable.

8-pin "HSSDC" cable connector (High Speed Serial Data Connection)

Optional pins 2, 4, 5, and 7 are intended

for use with an external optical converter.

This is often called a Media Interface

Assembly (MIA).

40-pin "SCA-2" disk connector

Although SCA-2 is the official name for this connector, it is often called SCA-40 to distinguish it

by its pin count from other similar connectors.

Pin Signal name Comments 1 -EN Bypass Port 1 Output driven high when port 1 is operating correctly

2 +12V

3 +12V

4 +12V

5 -Parallel ESI Input to allow ESI operation using the SELx pins

6 -Drive Present

7 ACTLED Output to drive the activity LED cathode

8 Power Control

9 START1 Input to control spin-up behavior (see the Disk options section)

10 START2 Input to control spin-up behavior (see the Disk options section)

11 -EN Bypass Port 2 Output driven high when port 2 is operating correctly

12 SEL6 Device ID bit 6 / ESI write clock

13 SEL5 Device ID bit 5 / ESI read clock

14 SEL4 Device ID bit 4 / ESI acknowledge clock

15 SEL3 Device ID bit 3 / ESI bit 3

16 FLTLED Output to drive the fault LED cathode

17 DEVCTRL2 Input to control interface speed (see the Disk options section)

18 DEVCTRL1 Input to control interface speed (see the Disk options section)

Pin Signal name Comments

1 +OUT Fibre channel output

2 +5V Optional

3 Module Fault Detect Optional

4 Reserved

5 +IN Fibre channel input

6 -OUT Fibre channel output

7 Output Disable Optional

8 GND Optional, return for pin 2

9 -IN Fibre channel input

Pin Signal name Comments

1 +OUT Fibre channel output

2 GND Optional, return for pin 7

3 -OUT Fibre channel output

4 Module Fault Detect Optional

5 Output Disable Optional

6 -IN Fibre channel input

7 +5V Optional

8 +IN Fibre channel input

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19 +5V

20 +5V

21 +12V Charge

22 GND (12V)

23 GND (12V)

24 +IN1 Fibre channel input

25 -IN1 Fibre channel input

26 GND (12V)

27 +IN2 Fibre channel input

28 -IN2 Fibre channel input

29 GND (12V)

30 +OUT1 Fibre channel output

31 -OUT1 Fibre channel output

32 GND (5V)

33 +OUT2 Fibre channel output

34 -OUT2 Fibre channel output

35 GND (5V)

36 SEL2 Device ID bit 2 / ESI bit 2

37 SEL1 Device ID bit 1 / ESI bit 1

38 SEL0 Device ID bit 0 / ESI bit 0

39 DEVCTRL0 Input to control interface speed (see the Disk options section)

40 +5V CHARGE

Fibre Channel connectors

Fibre Channel connection

port to computer

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Serial AT Attachments

Serial ATA or simply SATA is the hard disk standard created to replace the

parallel ATA interface, also known as IDE. SATA provides a transfer rate of 150 MB/s or 300

MB/s against of a 133 MB/s maximum using the previous technology. The conventional IDE port

(now called parallel ATA or simply PATA) transfers data in parallel. The advantage of parallel

transmission over serial transmission is the higher speed of the former mode, seeing that several

bits are sent at the same time. Its major disadvantage, however, relates to noise. As many wires

have to be used (at least one for each bit to be sent per turn), one wire generates interference in

another. This is why ATA-66 and higher hard disks require a special, 80-wire cable. The difference

between this 80-wire cable and the normal 40-wire IDE cable is that it includes a ground wire

between each original wire, providing anti-interference shielding. Serial ATA, on the other hand,

transmits data in serial mode, i.e. one bit per time. Traditional thinking makes us to think that serial

transmission is slower than parallel transmission. This is only true if we are comparing

transmissions using the same clock rate. In this case parallel transmission will be at least eight

times faster, as it transmits at least eight bits (one byte) per clock cycle, compared to serial

transmission where only one bit is transmitted per clock cycle. However, if a higher clock rate is

used on serial transmission, it can be faster than parallel. That’s exactly what happens with Serial

ATA. The problem in increasing parallel transmission transfer rate is increasing the clock rate, as

the higher the clock rate, more problems with electromagnetic interference show up. Since serial

transmission uses just one wire to transmit data it has fewer problems with noise, allowing it to use

very high clock rates, achieving a higher transfer rate.

Serial ATA standard transfer rate is of 1,500 Mbps. As it uses 8B/10B coding where each

group of eight bits is coded into a 10-bit number, its effective clock rate is of 150 MB/s. Serial

ATA devices running at this standard speed are also known as SATA-150. Serial ATA II provides

new features such as Native Command Queuing (NCQ), plus a higher speed rate of 300 MB/s.

Devices that can run at this speed are called SATA-300. The next standard to be released will be

SATA-600. It is important to notice that SATA II and SATA-300 are not synonyms. One can build

a device that runs only at 150 MB/s but using new features provided by SATA II such as NCQ.

This device would be a SATA II device, even though it doesn’t run at 300 MB/s. NCQ increases

the hard disk drive performance by reordering the commands send by the computer.

It is also very important to notice that Serial ATA implements two separated data paths, one for

transmitting and another for receiving data. On parallel design only one data path is available,

which is shared for both data transmission and reception. Serial ATA cable consists in two pair of

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wires (one for transmission and the other for reception) using differential transmission. Three

ground wires are also used, so Serial ATA cable has seven wires. Another advantage of using serial

transmission is that fewer wires need to be used. Parallel IDE ports use a 40-pin connector and 80-

wire flat cables. Serial ATA ports use a seven-pin connector and seven-wire cable. This helps a lot

on the thermal side of the computer, as using thinner cables makes air to flow easier inside the PC

case.

Features

Hotplug All SATA devices support hotplugging. However, proper hotplug

support requires the device be running in its native command mode not via IDE emulation,

which requires AHCI. Some of the earliest SATA host adapters were not capable of this

and furthermore some popular Operating Systems, such as Windows XP, still do not

support AHCI.

Advanced Host Controller Interface As their standard interface, SATA controllers

use the Advanced Host Controller Interface, allowing advanced features of SATA such as

hotplug and NCQ. If AHCI is not enabled by the motherboard and chipset, SATA

controllers typically operate in "IDE emulation" mode which does not allow features of

devices to be accessed if the ATA/IDE standard does not support them. Windows device

drivers that are labeled as SATA are usually running in IDE emulation mode unless they

explicitly state that they are AHCI. While the drivers included with Windows XP do not

support AHCI, AHCI has been implemented by proprietary device drivers. Windows Vista,

FreeBSD, Linux with kernel version 2.6.19 onward, as well as Solaris and OpenSolaris

have native support for AHCI.

Throughput The current SATA specifications detail data transfer rates as high as

6 GBits/s per device. SATA uses only 4 signal lines cables are more compact and cheaper

than PATA. SATA supports hot-swapping and NCQ.

Evolution

SATA 1.5 (First generation) First-generation SATA interfaces, now known as

SATA 1.5 communicates at a rate of 1.5 GBits/s. Taking 8b/10b encoding overhead into

account, they have an actual encoded transfer rate of 1.2 GBits/s. The theoretical burst

throughput of SATA 1.5 is similar to that of PATA/133, but newer SATA devices offer

enhancements such as NCQ which improve performance in a multitasking environment.

However, high-performance flash drives can transfer data at up to 201 MB/s, SATA 1.5

does not provide sufficient throughput for these drives. During the initial period after SATA

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1.5 finalization, adapter and drive manufacturers used a "bridge chip" to convert existing

PATA designs for use with the SATA interface. Bridged drives have a SATA connector,

may include either or both kinds of power connectors, and generally perform identically to

their PATA equivalents. Most lack support for some SATA-specific features such as NCQ.

Bridged products gradually gave way to native SATA products.

SATA 3 GBits/s (Second generation) Soon after the introduction of SATA 1.5Gbit/s,

a number of shortcomings emerged. At the application level SATA could handle only one

pending transaction at a time like PATA. The SCSI interface has long been able to accept

multiple outstanding requests and service them in the order which minimizes response time.

This feature, NCQ, was adopted as an optional supported feature for SATA 1.5 GBit/s and

SATA 3 GBit/s devices. First-generation SATA devices operated at best a little faster than

parallel ATA/133 devices. Subsequently, a 3 GBit/s signaling rate was added to the physical

layer (PHY layer), effectively doubling maximum data throughput from 150 MB/s to

300 MB/s. For mechanical hard drives, SATA 3 GBit/s transfer rate is expected to satisfy

drive throughput requirements for sometime, as the fastest mechanical drives barely saturate

a SATA 1.5 GBit/s link. A SATA data cable rated for 1.5 GBit/s will handle current

mechanical drives without any loss of sustained and burst data transfer performance.

However, high-performance flash drives are approaching SATA 3 GBit/s transfer rate.

Given the importance of backward compatibility between SATA 1.5 GBit/s controllers and

SATA 3 GBit/s devices, SATA 3 GBit/s auto-negotiation sequence is designed to fall back

to SATA 1.5 GBit/s speed when in communication with such devices. In practice, some

older SATA controllers do not properly implement SATA speed negotiation. Affected

systems require the user to set the SATA 3 GBit/s peripherals to 1.5 GBit/s mode, generally

through the use of a jumper, however some drives lack this jumper. Chipsets known to have

this fault include the VIA VT8237 and VT8237R Southbridge, and the VIA VT6420,

VT6421A and VT6421L standalone SATA controllers. SiS's 760 and 964 chipsets also

initially exhibited this problem, though it can be rectified with an updated SATA controller

ROM.

SATA II (committee renamed SATA-IO) Popular usage refers to the SATA 3 Gbit/s

specification as Serial ATA II (SATA II or SATA2), contrary to the wishes of the Serial ATA

International Organization (SATA-IO) which defines the standard. SATA II was originally

the name of a committee defining updated SATA standards, of which the 3 Gbit/s standard

was just one.

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SATA 6 GBits/s (Third generation) Serial ATA International Organization

presented the draft specification of SATA 6 GBit/s physical layer and ratified its physical

layer specification in 2008. The full 3.0 standard was released in 2009. While even the

fastest conventional hard disk drives can barely saturate the original SATA 1.5 GBit/s

bandwidth, Solid State Disk drives are close to saturating the SATA 3 Gbit/s limit at

250 MB/s net read speed. Ten channels of fast flash can actually reach well over 500 MB/s

with new ONFI drives, so a move from SATA 3 Gbit/s to SATA 6 Gbit/s would benefit the

flash read speeds. As for the standard hard disks, the reads from their built-in DRAM cache

will end up faster across the new interface. The new specification contains the following

changes:

o A new NCQ streaming command to enable Isochronous data transfers for

bandwidth-hungry audio and video applications.

o An NCQ Management feature that helps optimize performance by enabling host

processing and management of outstanding NCQ commands.

o Improved power management capabilities.

o A small Low Insertion Force (LIF) connector for more compact 1.8-inch storage

devices.

o A connector designed to accommodate 7 mm optical disk drives for thinner and

lighter notebooks.

o Alignment with the INCITS ATA8-ACS standard.

The enhancements are generally aimed at improving quality of service for video streaming and high

priority interrupts. In addition, the standard continues to support distances up to a meter. The new

speeds may require higher power consumption for supporting chips, factors that new process

technologies and power management techniques are expected to mitigate. The new specification

can use existing SATA cables and connectors, although some OEMs are expected to upgrade host

connectors for the higher speeds. Also, the new standard is backwards compatible with SATA 3

Gbit/s. In order to avoid parallels to the common SATA II misnomer, the SATA-IO has compiled a

set of marketing guidelines for the new specification. The specification should be called Serial ATA

International Organization: Serial ATA Revision 3.0, and the technology itself is to be referred to

as SATA 6 GBit/s. A product using this standard should be called the SATA 6 Gbit/s.

Cables and connectors

Connectors and cables present the most visible differences between SATA and PATA drives.

Unlike PATA, the same connectors are used on 3.5" SATA hard disks for desktop and server

computers and 2.5" disks for portable or small computers, this allows 2.5" drives to be used in

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desktop computers with only a mounting bracket and no wiring adapter. There is a special

connector (eSATA) specified for external devices, and an optionally implemented provision for

clips to hold internal connectors firmly in place. SATA drives may be plugged into SAS controllers

and communicate on the same physical cable as native SAS disks, but SATA controllers cannot

handle SAS disks.

Serial ATA Data Connector

The SATA standard defines a data cable with seven conductors (3 grounds

and 4 active data lines in two pairs) and 8 mm wide wafer connectors on

each end. SATA cables can have lengths up to 1 metre (3.3 ft), and connect

one motherboard socket to one hard drive. SATA connectors and cables are

easier to fit in closed spaces and reduce obstructions to air cooling. They are

more susceptible to accidental unplugging and breakage than PATA, but

cables can be purchased that have a locking feature, whereby a small spring holds the plug in the

socket. Designers use a number of techniques to reduce the undesirable effects of such

unintentional coupling. One such technique used in SATA links is differential signaling.

Serial ATA Power Connector

The SATA standard specifies a different power connector than the

decades-old four-pin Molex connector found on pre-SATA devices.

Like the data cable, it is wafer-based, but its wider 15-pin shape

prevents accidental mis-identification and forced insertion of the

wrong connector type. Native SATA devices favor the SATA

power-connector, although some early SATA drives retained older

4-pin Molex in addition to the SATA power connector. Adapters

exist which can convert a 4-pin Molex connector to a SATA power

connector. However, because the 4-pin Molex connectors do not

provide 3.3 V power, these adapters provide only 5 V and 12 V

power and leave the 3.3 V lines unconnected. This precludes the use

of such adapters with drives that require 3.3 V power.

SATA features more pins than the traditional power connector for several reasons:

A third voltage is supplied, 3.3 V, in addition to the traditional 5 V and 12 V.

Pin Function

1 Ground

2 A+

3 A-

4 Ground

5 B-

6 B+

7 Ground

Pin Function

1 +3.3 V

2 +3.3 V

3 +3.3 V

4 Ground

5 Ground

6 Ground

7 +5 V

8 +5 V

9 +5 V

10 Ground

11 Reserved/Ground

12 Ground

13 +12 V

14 +12 V

15 +12 V

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Each voltage transmits through three pins ganged together, because the small contacts by

themselves cannot supply sufficient current for some devices. (Each pin should be able to

provide 1.5 A.)

Five pins ganged together provide ground.

For each of the three voltages, one of the three pins serves for hotplugging. The ground pins

and power pins 3, 7, and 13 are longer on the plug (located on the SATA device) so they

will connect first. A special hot-plug receptacle (on the cable or a backplane) can connect

ground pins 4 and 12 first. Pin 11 can function for staggered spinup, activity indication, or

nothing. Staggered spinup is used to prevent many drives from spinning up simultaneously,

as this may draw too much power. Activity is an indication of whether the drive is busy, and

is intended to give feedback to the user through a LED.

Topology

SATA uses a point-to-point architecture. The connection between the controller and the storage

device is direct. Modern PC systems usually have a SATA controller on the motherboard, or

installed in a PCI or PCI Express slot. Most SATA controllers have multiple SATA ports and

can be connected to multiple storage devices. There are also port expanders or multipliers

which allow multiple storage devices to be connected to a single SATA controller port.

Encoding

These high-speed transmission protocols use a logic encoding known as 8b/10b encoding. The

signal uses non-return to zero (NRZ) encoding with LVDS. In the 8b/10b encoding the data

sequence includes the synchronizing signal. This technique is known as clock data recovery,

because it does not use a separate synchronizing signal. Instead, it uses the serial signal's 0 to 1

transitions to recover the clock signal.

Backward and forward compatibility

SATA and PATA

At the device level, SATA and PATA (Parallel Advanced Technology Attachment) devices

remain completely incompatible they cannot be interconnected. At the application level, SATA

devices can be specified to look and act like PATA devices. Many motherboards offer a "legacy

mode" option which makes SATA drives appear to the OS like PATA drives on a standard

controller. This eases OS installation by not requiring a specific driver to be loaded during setup

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but sacrifices support for some features of SATA and generally disables some of the boards'

PATA or SATA ports since the standard PATA controller interface only supports 4 drives. The

common heritage of the ATA command set has enabled the proliferation of low-cost PATA to

SATA bridge-chips. Bridge-chips were widely used on PATA drives (before the completion of

native SATA drives) as well as stand-alone "dongles." When attached to a PATA drive, a

device-side dongle allows the PATA drive to function as a SATA drive. Host-side dongles

allow a motherboard PATA port to function as a SATA host port. The market has produced

powered enclosures for both PATA and SATA drives which interface to the PC through USB,

Firewire or eSATA, with the restrictions noted above. PCI cards with a SATA connector exist

that allow SATA drives to connect to legacy systems without SATA connectors.

SATA 1.5 Gbit/s and SATA 3 Gbit/s

The designers of SATA aimed for backward and forward compatibility with future revisions of

the SATA standard. According to the hard drive manufacturer Maxtor, motherboard host

controllers using the VIA and SIS chipsets VT8237, VT8237R, VT6420, VT6421L, SIS760,

SIS964 found on the ECS 755-A2 manufactured in 2003, do not support SATA 3 Gbit/s drives.

Additionally, these host controllers do not support SATA 3 Gbit/s optical disc drives. To

address interoperability problems, the largest hard drive manufacturer, Seagate/Maxtor, has

added a user-accessible jumper-switch known as the Force 150, to switch between 150 MB/s

and 300 MB/s operation. Users with a SATA 1.5 Gbit/s motherboard with one of the listed

chipsets should either buy an ordinary SATA 1.5 Gbit/s hard disk, buy a SATA 3 Gbit/s hard

disk with the user-accessible jumper, or buy a PCI or PCI-E card to add full SATA 3 Gbit/s

capability and compatibility. Western Digital uses a jumper setting called OPT1 Enabled to

force 150 MB/s data transfer speed. OPT1 is used by putting the jumper on pins 5 & 6.

Comparisons with other interfaces

SATA and SCSI

SCSI currently offers transfer rates higher than SATA, but it uses a more complex bus, usually

resulting in higher manufacturing costs. SCSI buses also allow connection of several drives

(using multiple channels, 7 or 15 on each channel), whereas SATA allows one drive per

channel, unless using a port multiplier.

SATA 3 Gbit/s offers a maximum bandwidth of 300 MB/s per device compared to SCSI

with a maximum of 320 MB/s. Also, SCSI drives provide greater sustained throughput than

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SATA drives because of disconnect-reconnect and aggregating performance. SATA devices

generally link compatibly to SAS enclosures and adapters, while SCSI devices cannot be

directly connected to a SATA bus.

SCSI, SAS and fibre-channel (FC) drives are typically more expensive so they are

traditionally used in servers and disk arrays where the added cost is justifiable. Inexpensive

ATA and SATA drives evolved in the home-computer market, hence there is a view that

they are less reliable. As those two worlds overlapped, the subject of reliability became

somewhat controversial. Note that, generally, the failure rate of a disk drive is related to the

quality of its heads, platters and supporting manufacturing processes, not to its interface.

SATA in comparison to other buses

Name

Raw

bandwidth

(MBit/s)

Transfer

speed

(MB/s)

Max. cable length (m) Power

provided

Devices per

Channel

eSATA 3,000 300 2 with eSATA HBA

(1 with passive adapter) No

1 (15 with port

multiplier)

SATA 300 3,000 300 1 No 1 (15 with port

multiplier) SATA 150 1,500 150 1 No 1 per line PATA 133 1,064 133 0.46 (18 in) No 2

SAS 300 3,000 300 8 No 1 (16k with

expanders)

SAS 150 1,500 150 8 No 1 (16k with

expanders) FireWire

3200 3,144 393

100; alternate cables

available for >100 m 15 W, 12–

25 V 63 (with hub)

FireWire

800 786 98.25 100

15 W, 12–

25 V 63 (with hub)

FireWire

400 393 49.13 4.5

15 W, 12–

25 V 63 (with hub)

USB 3.0 5,000 625 3 4.5 W, 5 V 127 (with hub) USB 2.0 480 60 5 2.5 W, 5 V 127 (with hub) Ultra-320

SCSI 2,560 320 12 No

15 (plus the

HBA) Fibre

Channel

over optic

fiber

10,520 2,000 2–50,000 No 126

(16,777,216

with switches)

Fibre

Channel

over copper

cable

4,000 400 12 No 126

(16,777,216

with switches)

InfiniBand

12× Quad-

rate 120,000 12,000

5 (copper)

<10,000 (fiber) No

1 with point to

point

Many with

switched fabric

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Port Multiplier

Port Multiplier is a device that expands the number of devices to be installed on a single SATA

port. Port multiplier has several applications, like allowing a home user to install more than one

hard. Using port multiplier it is possible to connect them using fewer cables. For example, one port

multiplier connected to one SATA port allows you to connect up to 15 hard disk drives to it. And

you would have only one cable connecting the rack to the server. But there is a huge performance

issue here. If a SATA-150 port were used, the 150 MB/s bandwidth would have to be split between

15 devices, creating a huge bottleneck. To solve this issue another approach may be used. Instead

of using only one port multiplier chip, you could use four of them, connecting the rack to the server

using four cables (instead of 16). The maximum transfer rate between the server and the rack would

be of 600 MB/s (4x 150 MB/s) if SATA-150

ports were used or of 1,200 MB/s (4x 300

MB/s) if SATA-300 were used. Inside the

rack, you could install up to 60 hard disk

drives (15 x 4), but for optimal performance

you should install four hard disk drives to

each port multiplier chip, matching your 16

drives.

Block to explain Multi port HDD SATA

Port Multiplier Card

SATA Power Cable

eSATA and SATA cable

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Serial Attached SCSI

A typical Serial Attached SCSI system consists of the following basic components:

1. Initiator: a device that originates device-service and task-management requests for

processing by a target device and receives responses for the same requests from other target

devices. Initiators may be provided as an on-board component on the motherboard (as is the

case with many server-oriented motherboards) or as an add-on host bus adapter.

2. Target: a device containing logical units and target ports that receives device service and

task management requests for processing and sends responses for the same requests to

initiator devices. A target device could be a hard disk or a disk array system.

3. Service Delivery Subsystem: the part of an I/O system that transmits information between

an initiator and a target. Typically cables connecting an initiator and target with or without

expanders and backplanes constitute a service delivery subsystem.

4. Expanders: devices that form part of a service delivery subsystem and facilitate

communication between SAS devices. Expanders facilitate the connection of multiple SAS

End devices to a single initiator port.

SAS v/s Parallel SCSI

The SAS bus operates point-to-point while the SCSI bus is multidrop. Each SAS device is

connected by a dedicated link to the initiator, unless an expander is used. If one initiator is

connected to one target, there is no opportunity for contention, with parallel SCSI, even this

situation could cause contention.

SAS has no termination issues and does not require terminator packs like parallel SCSI.

SAS eliminates clock skew.

SAS supports up to 16,384 devices through the use of expanders, while Parallel SCSI has a

limit of 8 or 16 devices on a single channel.

SAS supports a higher transfer speed (3 or 6 GBit/s) than most parallel SCSI standards.

SAS achieves these speeds on each initiator-target connection, hence getting higher

throughput, whereas parallel SCSI shares the speed across the entire multidrop bus.

SAS controllers may support connecting to SATA devices, either directly connected using

native SATA protocol or through SAS expanders using SATA Tunneled Protocol (STP).

Both SAS and parallel SCSI use the SCSI command-set.

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SAS v/s SATA

Systems identify SATA devices by their port number connected to the host bus adapter,

while SAS devices are uniquely identified by their World Wide Name (WWN).

SAS protocol supports multiple initiators in a SAS domain, while SATA has no analogous

provision.

Most SAS drives provide tagged command queuing, while most newer SATA drives

provide native command queuing, each of which has its pros and cons.

SATA follows the ATA command set and thus only supports hard drives and CD/DVD

drives. In theory, SAS also supports numerous other devices including scanners and

printers. However, this advantage could also be moot, as most such devices have also found

alternative paths via such buses as USB, IEEE 1394 (FireWire), and Ethernet.

SAS hardware allows multipath I/O to devices while SATA (prior to SATA 3Gb/s) does

not. Per specification, SATA 3Gb/s makes use of port multipliers to achieve port expansion.

Some port multiplier manufacturers have implemented multipath I/O using port multiplier

hardware.

SATA is marketed as a general-purpose successor to parallel ATA and has become

common in the consumer market, whereas the more-expensive SAS targets critical server

applications.

SAS error-recovery and error-reporting use SCSI commands which have more functionality

than the ATA SMART commands used by SATA drives.

SAS uses higher signaling voltages (800-1600 mV TX, 275-1600 mV RX) than SATA

(400-600 mV TX, 325-600 mV RX). The higher voltage offers (among other features) the

ability to use SAS in server backplanes.

Because of its higher signaling voltages, SAS can use cables up to 8 m (26 ft) long, SATA

has a cable-length limit of 1 m (3 ft).

SAS Protocols

SAS uses a few protocols to deal with a few different type of traffic flowing through it. It is worth

mentioning them here because they are used a lot in talking about SAS.

SSP stands for ―Serial SCSI Protocol‖ which encapsulates "legacy" SCSI commands and data for

transmission between nodes. For example, if node "x" sends node "y" a command to "read data

block 54", and node "y" sends back the data from that disk block, this transaction is done with SSP,

which encapsulates the SCSI Command Block (CDB), the data, the "sense data" (error data, if

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needed), and other basic information which is used in any SCSI transaction, parallel, serial, legacy,

whatever.

SMP stands for "SAS Management Protocol". It is used only by expanders and initiators (hosts).

SMP provides a set of very simple commands to allow initiators and expanders to query

information from each other. This is only done at start-up, or when a devices is added or removed

from the bus. SMP is used to allow the initiator/host to discover what devices are on the SAS bus,

so it may assign SCSI IDs to them and present them to the host. It is also used to allow the

expanders to see what devices (WWNs) are connected off which ports of other expanders, so they

will know how to open routes to different devices/WWNs. This sharing of information between

initiators and expanders whenever the bus is new or changed, is called "discovery". It is simply,

everyone asking their neighbors about who their neighbors are and collecting everyone’s addresses

so ,for example, expanders will know through which port messages to different addresses should be

routed.

STP stands for "SAS Tunneling Protocol". This is simply the mechanism that a SAS topology uses

to talk to, and route commands from/to SATA (Serial-ATA) devices. SATA devices use a wire

level signaling that it somewhat similar to SAS, but outside of that, are quite different. SATA

devices can be connected to a SAS topology however, and STP is used to tunnel this different data

from a host, through the SAS network, to a SATA device.

Architecture

SAS architecture consists of six layers:

Physical layer:

o defines electrical and physical characteristics

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o differential signaling transmission

o Three connector types:

SFF 8482 – SATA compatible

SFF 8484 – up to four devices

SFF 8470 – external connector (InfiniBand connector), up to four devices

PHY Layer:

o 8b/10b data encoding

o Link initialization, speed negotiation and reset sequences

o Link capabilities negotiation (SAS-2)

Link layer:

o Insertion and deletion of primitives for clock-speed disparity matching

o Primitive encoding

o Data scrambling for reduced EMI

o Establish and tear down native connections between SAS targets and initiators

o Establish and tear down tunneled connections between SAS initiators and SATA

targets connected to SAS expanders

o Power management (proposed for SAS-2.1)

Port layer:

o Combining multiple PHYs with the same addresses into wide ports

Transport layer:

o Supports three transport protocols:

Serial SCSI Protocol (SSP): supports SAS devices

Serial ATA Tunneled Protocol (STP): supports SATA devices attached to

SAS expanders

Serial Management Protocol (SMP): provides for the configuration of SAS

expanders

Application layer

SAS Expanders

The components known as Serial Attached SCSI Expanders (SAS Expanders) facilitate

communication between large numbers of SAS devices. Expanders contain two or more external

expander-ports. Each expander device contains at least one SAS Management Protocol target port

for management and may contain SAS devices itself. For example, an expander may include a

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Serial SCSI Protocol target port for access to a peripheral device. There are two different types of

expander: Edge Expanders and Fanout Expanders.

An edge expander allows for communication with up to 128 SAS addresses, allowing the

SAS initiator to communicate with these additional devices. Edge expanders can do direct

table routing and subtractive routing. Without a fanout expander, we can use at most two

edge expanders in our delivery subsystem

A fanout expander can connect up to 128 sets of edge expanders, known as an edge

expander device set, allowing for even more SAS devices to be addressed. The subtractive

routing port of each edge expanders will be connected to the phys of fanout expander. A

fanout expander can not do subtractive routing, it can only forward subtractive routing

requests to the connected edge expanders.

Connectors

The SAS connector is much smaller than traditional parallel SCSI connectors, allowing for the

small 2.5-inch (64 mm) drives. SAS currently supports point data transfer speeds up to 6 Gbit/s, but

is expected to reach 12 GBit/s in near future

SFF 8482,SATA connector, Internal

connector ,connected with 1 device, Form-

factor compatible with SATA: allows for

SATA drives to connect to a SAS backplane, which obviates the need to install an additional SATA

controller just to attach a DVD-writer, for example. Note that SAS drives are not usable on a SATA

bus and have their physical connector keyed to prevent any plugging into a SATA backplane.

SFF 8484,Internal connector with 32 pins and can be connected to 4

devices, Hi-density internal connector, 2 and 4 lane versions are defined

by the SFF standard.

SFF 8470,Infiniband connector is an External connector with 32 pins and

can be connected to 4 devices, Hi-density external connector (also used as

an internal connector)

SFF 8088,External mini-SAS, External mSAS connector with 26 pins and

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can be connected to 4 devices, Molex iPASS reduced width external 4× connector with future

10 Gbit/s support

External Device Interfaces

External Devices can be interfaced using interfacing technologies like Parallel Port (LPT), Serial

port USB and PS/2 connectors; the following describes them.

Parallel Port (LPT)

A parallel port is a type of interface found on computers (personal and otherwise) for connecting

various peripherals. It is also known as a printer port or Centronics port. The Parallel Port is the

most commonly used port for interfacing home made projects. This port will allow the input of up

to 9 bits or the output of 12 bits at any one given time, thus requiring minimal external circuitry to

implement many simpler tasks. The port is composed of 4 control lines, 5 status lines and 8 data

lines. It's found commonly on the back PC as a D-Type 25 Pin female connector. There may also be

a D-Type 25 pin male connector. This will be a serial RS-232 port and thus, is a totally

incompatible port. Parallel port works in 5 modes which are as follows,

1. Compatibility Mode.

2. Nibble Mode. (Protocol not Described in this Document)

3. Byte Mode. (Protocol not Described in this Document)

4. EPP Mode (Enhanced Parallel Port).

5. ECP Mode (Extended Capabilities Mode).

The aim was to design new drivers and devices which were compatible with each other and also

backwards compatible with the Standard Parallel Port (SPP). Compatibility, Nibble & Byte modes

use just the standard hardware available on the original Parallel Port cards while EPP & ECP

modes require additional hardware which can run at faster speeds, while still being downwards

compatible with the Standard Parallel Port. Compatibility mode or "Centronics Mode" as it is

commonly known, can only send data in the forward direction at a typical speed of 50 Kbytes/sec

but can be as high as 150+ Kbytes/sec. In order to receive data, you must change the mode to either

Nibble or Byte mode. Nibble mode can input a nibble (4 bits) in the reverse direction. E.g. from

device to computer. Byte mode uses the Parallel's bi-directional feature (found only on some cards)

to input a byte (8 bits) of data in the reverse direction. Extended and Enhanced Parallel Ports use

additional hardware to generate and manage handshaking. To output a byte to a printer (or anything

in that matter) using compatibility mode, the software must,

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1. Write the byte to the Data Port.

2. Check to see is the printer is busy. If the printer is busy, it will not accept any

data, thus any data which is written will be lost.

3. Take the Strobe (Pin 1) low. This tells the printer that there is the correct data on

the data lines. (Pins 2-9)

4. Put the strobe high again after waiting approximately 5 microseconds after

putting the strobe low. (Step 3)

This limits the speed at which the port can run at. The EPP & ECP ports get around this by letting

the hardware check to see if the printer is busy and generate a strobe and /or appropriate

handshaking. This means only one I/O instruction need to be performed, thus increasing the speed.

These ports can output at around 1-2 megabytes per second. The ECP port also has the advantage

of using DMA channels and FIFO buffers, thus data can be shifted around without using I/O

instructions.

Hardware Properties

Below is a table of the "Pin Outs" of the D-Type 25 Pin connector and the Centronics 34 Pin

connector. The D-Type 25 pin connector is the most common connector found on the Parallel Port

of the computer, while the Centronics Connector is commonly found on printers. The IEEE 1284

standard however specifies 3 different connectors for use with the Parallel Port. The first one, 1284

Type A is the D-Type 25 connector found on the back of most computers. The 2nd is the 1284

Type B which is the 36 pin Centronics Connector found on most printers.

Pin No

(D-Type

25)

Pin No

(Centronic

s)

SPP Signal Directio

n In/out

Registe

r

1 1 nStrobe In/Out Control

2 2 Data 0 Out Data

3 3 Data 1 Out Data

4 4 Data 2 Out Data

5 5 Data 3 Out Data

6 6 Data 4 Out Data

7 7 Data 5 Out Data

8 8 Data 6 Out Data

9 9 Data 7 Out Data

10 10 nAck In Status

11 11 Busy In Status

12 12 Paper-Out /

Paper-End

In Status

13 13 Select In Status

14 14 nAuto-Linefeed In/Out Control

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The output of the Parallel Port is

normally TTL logic levels. The

voltage levels are the easy part.

The current you can sink and

source varies from port to port. Most Parallel Ports implemented in ASIC, can sink and

source around 12mA. However these are just some of the figures taken from Data sheets,

Sink/Source 6mA, Source 12mA/Sink 20mA, Sink 16mA/Source 4mA, Sink/Source 12mA.

Centronics

Centronics is an early standard for transferring data from a host to the printer. The majority of

printers use this handshake. This handshake is normally implemented using a Standard Parallel Port

under software control. Below is a simplified diagram of the `Centronics' Protocol.

Data is first applied on the Parallel Port pins 2 to

7. The host then checks to see if the printer is

busy. i.e. the busy line should be low. The

program then asserts the strobe, waits a minimum

of 1uS, and then de-asserts the strobe. Data is

normally read by the printer/peripheral on the

rising edge of the strobe. The printer will indicate

that it is busy processing data via the Busy line. Once the printer has accepted data, it will

acknowledge the byte by a negative pulse about 5uS on the nAck line.Quite often the host will

ignore the nAck line to save time. Latter in the Extended Capabilities Port, the hardware do all the

handshaking for you. All the programmer must do is write the byte of data to the I/O port. The

hardware will check to see if the printer is busy, generate the strobe. Note that this mode commonly

doesn't check the nAck either.

Port Addresses

The Parallel Port has three commonly used base addresses. The 3BCh base address was originally

introduced used for Parallel Ports on early Video Cards. This address then disappeared for a while,

when Parallel Ports were later removed from Video Cards. They has now reappeared as an option

for Parallel Ports integrated onto motherboards, upon which their configuration can be changed

using BIOS. LPT1 is normally assigned base address 378h, while LPT2 is assigned 278h. 378h &

15 32 nError / nFault In Status

16 31 nInitialize In/Out Control

17 36 nSelect-Printer /

nSelect-In

In/Out Control

18 - 25 19-30 Ground Gnd

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278h have always been commonly used for Parallel Ports. These addresses may change from

machine to machine.

Address Notes:

3BCh - 3BFh Used for Parallel Ports which were incorporated on to

Video Cards - Doesn't support ECP addresses

378h - 37Fh Usual Address For LPT 1

278h - 27Fh Usual Address For LPT 2

When the computer is first turned on, BIOS (Basic Input/Output System) will determine the

number of ports you have and assign device labels LPT1, LPT2 & LPT3 to them. BIOS first looks

at address 3BCh. If a Parallel Port is found here, it is assigned as LPT1, then it searches at location

378h. If a Parallel card is found there, it is assigned the next free device label. This would be LPT1

if a card wasn't found at 3BCh or LPT2 if a card was found at 3BCh. The last port of call, is 278h

and follows the same procedure than the other two ports. Therefore it is possible to have a LPT2

which is at 378h and not at the expected address 278h. What can make this even confusing, is that

some manufacturers of Parallel Port Cards, have jumpers which allow you to set your Port to LPT1,

LPT2, LPT3. Now what address is LPT1? - On the majority of cards LPT1 is 378h, and LPT2,

278h, but some will use 3BCh as LPT1, 378h as LPT1 and 278h as LPT2. The assigned devices

LPT1, LPT2 & LPT3 should not be a worry to people wishing to interface devices to their PC's.

Most of the time the base address is used to interface the port rather than LPT1 etc. However to

find the address of LPT1 or any of the Line Printer Devices, we can use a lookup table provided by

BIOS.

Start Address Function

0000:0408 LPT1's Base Address

0000:040A LPT2's Base Address

0000:040C LPT3's Base Address

0000:040E LPT4's Base Address (Note 1)

Parallel Port Modes in BIOS

Today, most Parallel Ports are multimode ports. They are normally software configurable to one of

many modes from BIOS. The following modes are configurable via BIOS. The typical modes are,

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Printer Mode

Standard & Bi-directional (SPP) Mode

EPP1.7 and SPP Mode

EPP1.9 and SPP Mode

ECP Mode

ECP and EPP1.7 Mode

ECP and EPP1.9 Mode

Printer Mode is the most basic mode. It is a Standard Parallel Port in forward mode only. It has no

bi-directional feature, thus Bit 5 of the Control Port will not respond. Standard & Bi-directional

(SPP) Mode is the bi-directional mode. Using this mode, bit 5 of the Control Port will reverse the

direction of the port, so you can read back a value on the data lines.

EPP1.7 and SPP Mode is a combination of EPP 1.7 (Enhanced Parallel Port) and SPP Modes. In

this mode of operation you will have access to the SPP registers (Data, Status and Control) and

access to the EPP Registers. In this mode you should be able to reverse the direction of the port

using bit 5 of the control register. EPP 1.7 is the earlier version of EPP.

EPP1.9 and SPP Mode is just like the previous mode, only it uses EPP Version 1.9 this time. As in

the other mode, you will have access to the SPP registers, including Bit 5 of the control port.

However this differs from EPP1.7 and SPP Mode as you should have access to the EPP Timeout

bit.

ECP Mode will give you an Extended Capabilities Port. The mode of this port can then be set using

the ECP's Extended Control Register (ECR). However in this mode from BIOS the EPP Mode

(100) will not be available.

ECP and EPP1.7 Mode and ECP and EPP1.9 Mode will give you an Extended Capabilities Port,

just like the previous mode. However the EPP Mode in the ECP's ECR will now be available.

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Pin configuration

LPT Male and Female cable

Serial Port

Serial port is a serial communication physical interface through which information transfers in or

out one bit at a time (contrast parallel port). While such interfaces as Ethernet, FireWire, and USB

all send data as a serial stream, the term "serial port" usually identifies hardware more or less

compliant to the RS-232 standard, intended to interface with a modem or with a similar

communication device. For its use to connect peripheral devices, the serial port has largely been

replaced by USB and Firewire. For networking, it has been replaced by Ethernet. Serial ports are

commonly still used in legacy applications such as industrial automation systems, scientific

analysis, shop till systems and some industrial and consumer products. Network equipment (such as

routers and switches) often use serial console for configuration. Serial ports are still used in these

areas as they are simple, cheap and their console functions (RS-232) are highly standardized and

widespread. The vast majority of computer systems have a serial port, however it must usually be

wired manually and sometimes there are no pins in the manufactured version.

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Hardware

Some computers, such as the IBM PC, used an integrated circuit called a UART, that converted

characters to (and from) asynchronous serial form, and automatically looked after the timing and

framing of data. Very low-cost systems, such as some early home computers, would instead use the

CPU to send the data through an output pin, using the so-called bit-banging technique. Many

personal computer motherboards still have at least one serial port. Small-form-factor systems and

laptops may omit RS-232 connector ports to conserve space, but the electronics are still there. RS-

232 has been standard for so long that the circuits needed to control a serial port became very cheap

and often exist on a single chip, sometimes also with circuitry for a parallel port. Early home

computers often had proprietary serial ports with pinouts and voltage levels incompatible with RS-

232. Inter-operation with RS-232 devices may be impossible as the serial port cannot withstand the

voltage levels produced and may have other differences that "lock in" the user to products of a

particular manufacturer. Low-cost processors now allow higher-speed, but more complex, serial

communication standards such as USB and FireWire to replace RS-232. These make it possible to

connect devices that would not have operated feasibly over slower serial connections, such as mass

storage, sound, and video devices.

Connectors

While the RS-232 standard originally specified a 25-pin D-type connector, many designers of

personal computers chose to implement only a subset of the full standard: they traded off

compatibility with the standard against the use of less costly and more compact connectors (in

particular the DE-9 version used by the original IBM PC-AT). Starting around the time of the

introduction of the IBM PC-AT, serial ports were commonly built with a 9-pin connector to save

cost and space. However, presence of a nine pin D-subminiature connector is neither necessary nor

sufficient to indicate use of a serial port, since this connector was also used for video, joysticks, and

other purposes. Some miniaturized electronics, particularly graphing calculators and to a lesser

extent hand-held amateur and two-way radio equipment, have serial ports using a jack plug

connector, usually the smaller 2.5 or 3.5 mm connectors and use the most basic 3-wire interface.

Many models of Macintosh favored the related (but faster) RS-422 standard, mostly using German

Mini-DIN connectors, except in the earliest models. The Macintosh included a standard set of two

ports for connection to a printer and a modem, but some PowerBook laptops had only one

combined port to save space.

Pinouts

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The following table lists commonly-used RS-232 signals and pin assignments

Signal Origin DB-25 DE-9

(TIA-574) Name Abbreviation DTE DCE

Common Ground G 7 5

Protective Ground PG 1 -

Transmitted Data TxD ● 2 3

Received Data RxD ● 3 2

Data Terminal Ready DTR ● 20 4

Data Set Ready DSR ● 6 6

Request To Send RTS ● 4 7

Clear To Send CTS ● 5 8

Carrier Detect DCD ● 8 1

Ring Indicator RI ● 22 9

Signals

Transmitted Data (TxD) Data sent from DTE to DCE.

Received Data (RxD) Data sent from DCE to DTE.

Request To Send (RTS) Asserted (set to logic 0, positive voltage) by DTE to prepare DCE to

receive data. This may require action on the part of the DCE, e.g. transmitting a carrier or reversing

the direction of a half-duplex channel. For the modern usage of "RTS/CTS handshaking," see the

section of that name.

Ready To Receive (RTR) Asserted by DTE to indicate to DCE that DTE is ready to receive data. If

in use, this signal appears on the pin that would otherwise be used for Request To Send, and the

DCE assumes that RTS is always asserted; see RTS/CTS handshaking for details.

Clear To Send (CTS) Asserted by DCE to acknowledge RTS and allow DTE to transmit. This

signaling was originally used with half-duplex modems and by slave terminals on multidrop lines:

The DTE would raise RTS to indicate that it had data to send, and the modem would raise CTS to

indicate that transmission was possible. For the modern usage of "RTS/CTS handshaking," see the

section of that name.

Data Terminal Ready (DTR) Asserted by DTE to indicate that it is ready to be connected. If the

DCE is a modem, this may "wake up" the modem, bringing it out of a power saving mode. This

behavior is seen quite often in modern PSTN and GSM modems. When this signal is de-asserted,

the modem may return to its standby mode, immediately hanging up any calls in progress.

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Data Set Ready (DSR) Asserted by DCE to indicate the DCE is powered on and is ready to

receive commands or data for transmission from the DTE. For example, if the DCE is a modem,

DSR is asserted as soon as the modem is ready to receive dialing or other commands; DSR is not

dependent on the connection to the remote DCE (see Data Carrier Detect for that function). If the

DCE is not a modem (e.g. a null modem cable or other equipment), this signal should be

permanently asserted (set to 0), possibly by a jumper to another signal.

Data Carrier Detect (DCD) Asserted by DCE when a connection has been established with remote

equipment.

Ring Indicator (RI) Asserted by DCE when it detects a ring signal from the telephone line.

Universal Serial Bus

A USB system has an asymmetric design, consisting of a host, a multitude of downstream USB

ports, and multiple peripheral devices connected in a tiered-star topology. Additional USB hubs

may be included in the tiers, allowing branching into a tree structure with up to five tier levels. A

USB host may have multiple host controllers and each host controller may provide one or more

USB ports. Up to 127 devices, including the hub devices, may be connected to a single host

controller. USB devices are linked in series through hubs. There always exists one hub known as

the root hub, which is built into the host controller. So-called sharing hubs, which allow multiple

computers to access the same peripheral device(s), also exist and work by switching access

between PCs, either automatically or manually. They are popular in small-office environments. In

network terms, they converge rather than diverge branches. A physical USB device may consist of

several logical sub-devices that are referred to as device functions. A single device may provide

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several functions, for example, a webcam (video device function) with a built-in microphone (audio

device function). Such a device is called a compound device in which each logical device is

assigned a distinctive address by the host and all logical devices are connected to a built-in hub to

which the physical USB wire is connected. A host assigns one and only one device address to a

function. USB device communication is based on pipes (logical channels). Pipes are connections

from the host controller to a logical entity on the device named an endpoint. The term endpoint is

occasionally used to incorrectly refer to the pipe because, while an endpoint exists on the device

permanently, a pipe is only formed when the host makes a connection to the endpoint. Therefore,

when referring to the connection between a host and an endpoint, the term pipe should be used. A

USB device can have up to 32 active pipes, 16 into the host controller and 16 out of the controller.

There are two types of pipes: stream and message pipes. A stream pipe is a uni-directional pipe

connected to a uni-directional endpoint that is used for bulk, interrupt, and isochronous data flow

while a message pipe is a bi-directional pipe connected to a bi-directional endpoint that is

exclusively used for control data flow. An endpoint is made into the USB device by the

manufacturer, and therefore, exists permanently. An endpoint of a pipe is addressable with tuple

(device_address, endpoint_number) as specified in a TOKEN packet that the host sends when it

wants to start a data transfer session. If the direction of the data transfer is from the host to the

endpoint, an OUT packet, which is a specialization of a TOKEN packet, having the desired device

address and endpoint number is sent by the host. If the direction of the data transfer is from the

device to the host, the host sends an IN packet instead. If the destination endpoint is a uni-

directional endpoint whose manufacturer's designated direction does not match the TOKEN packet

(e.g., the manufacturer's designated direction is IN while the TOKEN packet is an OUT packet), the

TOKEN packet will be ignored. Otherwise, it will be accepted and the data transaction can start. A

bi-directional endpoint, on the other hand, accepts both IN and OUT packets. Endpoints are

grouped into interfaces and each interface is associated with a single device function. An exception

to this is endpoint zero, which is used for device configuration and which is not associated with any

interface. A single device function comprises of independently controlled interfaces is called a

composite device. A composite device only has a single device address because the host only

assigns a device address to a function. When a USB device is first connected to a USB host, the

USB device enumeration process is started. The enumeration starts by sending a reset signal to the

USB device. The speed of the USB device is determined during the reset signaling. After reset, the

USB device's information is read by the host, then the device is assigned a unique 7-bit address. If

the device is supported by the host, the device drivers needed for communicating with the device

are loaded and the device is set to a configured state. If the USB host is restarted, the enumeration

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process is repeated for all connected devices. The host controller directs traffic flow to devices, so

no USB device can transfer any data on the bus without an explicit request from the host controller.

In USB 2.0, the host controller polls the bus for traffic, usually in a round-robin fashion. The

slowest device connected to a controller sets the speed of the interface. For SuperSpeed USB (USB

3.0), connected devices can request service from host, and because there are two separate

controllers in each USB 3.0 host, USB 3.0 devices will transmit and receive at USB 3.0 speeds,

regardless of USB 2.0 or earlier devices connected to that host. Operating speeds for them will be

set in the legacy manner.

PinOut

Pin Signal Color Description

1 VCC Red +5V

2 D- White Data -

3 D+ Green Data +

4 GND Black Ground

Glossary

Direct Attached Storage (DAS) refers to a digital storage system directly attached to a server or

workstation, without a storage network in between. DAS system is made of a data storage device

connected directly to a computer through a host bus adapter. Between those two points there is no

network device (like hub, switch, or router), and this is the main characteristic of DAS. The main

protocols used for DAS connections are ATA, SATA, SCSI, SAS, and Fibre Channel. A DAS

device can be shared between multiple computers, if only it provides multiple interfaces (ports) that

allow concurrent and direct access. This way it can be usable for computer clusters. DAS can

enable storage capacity extension, while keeping high data bandwidth and access rate.

Network Attached Storage (NAS) is essentially a self-contained computer connected to a

network, with the sole purpose of supplying file-based data storage services to other devices on the

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network. The unit is not designed to carry out general-purpose computing tasks, although it may

technically be possible to run other software on it. NAS units usually do not have a keyboard or

display, and are controlled and configured over the network, often by connecting a browser to their

network address. The alternative to NAS storage on a network is to use a computer as a file server.

In its most basic form a dedicated file server is no more than a NAS unit with keyboard and display

and an operating system which, while optimised for providing storage services, can run other tasks.

Despite differences SAN and NAS are not exclusive and may be combined in one solution: SAN-

NAS hybrid.

Storage Area Network (SAN) is a high-speed special-purpose network (or sub-network) that

interconnects different kinds of data storage devices with associated data servers on behalf of a

larger network of users. Typically, a storage area network is part of the overall network of

computing resources for an enterprise. A storage area network is usually clustered in close

proximity to other computing resources such as IBM z990 mainframes but may also extend to

remote locations for backup and archival storage, using wide area network carrier technologies

such as ATM or SONET.

INCITS International Committee for Information Technology Standards, is an ANSI-accredited

forum of IT developers. It was formerly known as the X3 and NCITS.INCITS technical standard

groups and technical committees have provided many popular standards, among them are T10 -

SCSI, T11 (X3T9.3) - Fibre Channel and T13 - AT Attachment. INCITS coordinates technical

standards activity between ANSI in the USA and joint ISO/IEC committees worldwide. This

provides a mechanism to create standards that will be implemented in many nations.

UDMA (with CRC) or Ultra Direct Memory Access was double transition clocking. Before Ultra

DMA, one transfer of data occurred on each clock cycle, triggered by the rising edge of the

interface clock (or "strobe"). With Ultra DMA, data is transferred on both the rising and falling

edges of the clock. Ultra DMA also introduced the use of cyclical redundancy checking or CRC on

the interface. The device sending data uses the CRC algorithm to calculate redundant information

from each block of data sent over the interface. This "CRC code" is sent along with the data. On the

other end of the interface, the recipient of the data does the same CRC calculation and compares its

result to the code the sender delivered. If there is a mismatch, this means data was corrupted

somehow and the block of data is resent. If errors occur frequently, the system may determine that

there are hardware issues and thus drop down to a slower Ultra DMA mode, or even disable Ultra

DMA operation.

Memory Unit Conversion Table

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Decimal Symbol Name Binary Equivalent

103 K Kilo 2

10=1024

106 M Mega 2

20=1024 K

109 G Giga 2

30=1024 M

1012

T Tera 240

=1024 G

1015

P Peta 250

=1024 T

1018

E Exa 260

=1024 P

1021

Z Zetta 270

=1024 E

1024

Y Yotta 280

=1024 Z

SCA Serial Connector Attachment, is a type of connection for the internal cabling of SCSI

systems. There are two versions of this connector: the SCA-1, which is deprecated, and SCA-2,

which is currently in use in most systems. In addition there are Single-Ended (SE) and Low

Voltage Differential (LVD) types of the SCA.

RAID Redundant Array of Inexpensive Disks is a technology that allowed computer users to

achieve high levels of storage reliability from low-cost and less reliable PC-class disk-drive

components, via the technique of arranging the devices into arrays for redundancy."RAID" is now

used as an umbrella term for computer data storage schemes that can divide and replicate data

among multiple hard disk drives.

ST-506 was the first 5.25 inch hard disk drive. Introduced in 1980 by Seagate Technology, it

stored up to 5 MB. The similar 10 MB ST-412 was introduced in late 1981 with enhanced bit rates.

ESDI or Enhanced Small Disk Interface was a disc interface designed by Maxtor Corporation in

the early 1980s to be a follow-on to the ST-506 interface. ESDI used the same cabling as ST-506

and could handle data rates of 10, 15, or 20 MBits/sec (as opposed to ST-506's top speed of 7.5

megabits), and many high-end SCSI drives of the era were actually high-end ESDI drives with

SCSI bridges integrated on the drive.

Hot swapping and hot plugging are terms used to separately describe the functions of replacing

system components without shutting down the system. Hot swapping describes changing

components without significant interruption to the system, while hot plugging describes changing

or adding components which interact with the operating system. Both terms describe the ability to

remove and replace components of a machine, usually a computer, while it is operating. For hot

swapping once the appropriate software is installed on the computer, a user can plug and unplug the

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component without rebooting. A well-known example of this functionality is the Universal Serial

Bus (USB) that allows users to add or remove peripheral components such as a mouse, keyboard,

or printer.

Native Command Queuing (NCQ) is a technology designed to increase performance of SATA

hard disks under certain situations by allowing the individual hard disk to internally optimize the

order in which received read and write commands are executed. This can reduce the amount of

unnecessary drive head movement, resulting in increased performance for workloads where

multiple simultaneous read/write requests are outstanding, most often occurring in server-type

applications.

Peripheral Component Interconnect(PCI) is a computer bus for attaching hardware devices in a

computer. These devices can take either the form of an integrated circuit fitted onto the

motherboard itself or a card fitted with motherboard. Typical PCI cards used in PCs include

network cards, sound cards, modems, extra ports such as USB or serial, TV tuner cards and disk

controllers.

Open NAND Flash Interface (ONFI) are the small n very fast drives for storage.

Low Insertion Force connectors are High-density metric (HDM) connectors from Molex are

designed for board-to-board connection in applications such as networking, high-end computing

and telecommunications equipment. HDM connectors offer a unique combination of robust

mechanical performance, high speed and high-density signal capability.

MultiDrop BUS is a computer bus in which all components are connected to the same set of

electrical wires. A process of arbitration determines which device gets the right to be the sender of

information at any point in time. The other devices must listen for the data that is intended to be

received by them.but electronically are limited to around 200–400 MHz (because of reflections on

the wire from the printed circuit board (PCB) onto the die) and 10–20 cm distance (SCSI-1 has 6

metres). Multidrop standards such as PCI are therefore being replaced by point-to-point.

Backpane (or "backplane system") is a circuit board (usually a printed circuit board) that connects

several connectors in parallel to each other, so that each pin of each connector is linked to the same

relative pin of all the other connectors forming a computer bus.

Different Voltage/Logic levels

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Terms -

VCC: The voltage applied to the power pin(s). In most cases the voltage the device needs to operate at.

VIH: [Voltage Input High] The minimum positive voltage applied to the input which will be accepted by the

device as a logic high.

VIL: [Voltage Input Low] The maximum positive voltage applied to the input which will be accepted by the

device as a logic low.

VOL: [Voltage Output Low] The maximum positive voltage from an output which the device considers will

be accepted as the maximum positive low level.

VOH: [Voltage Output High] The maximum positive voltage from an output which the device considers will

be accepted as the minimum positive high level.

VT: [Threshold Voltage] The voltage applied to a device which is "transition-Operated", which cause the

device to switch. May also be listed as a '+' or '-' value.

RS232 logic level

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Different Data Transmission Protocols

SPECIFICATIONS RS232 RS423 RS422 RS485

Mode of Operation SINGLE

-ENDED

SINGLE

-ENDED

DIFFERENTIAL DIFFERENTIAL

Total Number of Drivers and

Receivers on One Line (One

driver active at a time for RS485

networks)

1

DRIVER

1 RECVR

1

DRIVER

10

RECVR

1 DRIVER

10 RECVR

32 DRIVER

32 RECVR

Maximum Cable Length 50 FT. 4000 FT. 4000 FT. 4000 FT.

Maximum Data Rate (40ft. -

4000ft. for RS422/RS485)

20kb/s 100kb/s 10Mb/s-100Kb/s 10Mb/s-100Kb/s

Maximum Driver Output Voltage +/-25V +/-6V -0.25V to +6V -7V to +12V

Driver Output

Signal Level

(Loaded Min.)

Loaded +/-5V to

+/-15V

+/-3.6V +/-2.0V +/-1.5V

Driver Output

Signal Level

(Unloaded Max)

Unloaded +/-25V +/-6V +/-6V +/-6V

Driver Load Impedance (Ohms) 3k to 7k >=450 100 54

Max. Driver Current

in High Z State

Power On N/A N/A N/A +/-100uA

Max. Driver Current

in High Z State

Power Off +/-6mA

@ +/-2v

+/-100uA +/-100uA +/-100uA

Slew Rate (Max.) 30V/uS Adjustable N/A N/A

Receiver Input Voltage Range +/-15V +/-12V -10V to +10V -7V to +12V

Receiver Input Sensitivity +/-3V +/-200mV +/-200mV +/-200mV

Receiver Input Resistance

(Ohms), (1 Standard Load for

RS485)

3k to 7k 4k min. 4k min. >=12k

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Attention!!

This is to kindly request to all the readers of this report that if they find any

faults in this report or if they append this report to make it better, they are

heartily welcomed for feedbacks and they are requested to please inform me

through my mail id and they may send me the new report on it as well.

This way we all can help to propagate the knowledge in this world of

science.

Please help me in this process…

Shubham Pandey

shubham_143_onnet@yahoo.com