Group #6External Memory

Manuel FrancoMaria P Gil Palacios

Luis GuerreroJose Iraheta

Wilder Saint - Hillarie

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Read Mechanism

• Data is retrieved from the disk via a conducting coil called the head.

• The read head has a MR sensor which has an electrical resistance that depends on the direction of the magnetization of the disk under it.

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Write Mechanism

• The write also has it’s respective head, although it is possible for the sharing of read and write heads.

• Exploits the fact that electricity flowing through coil produces a magnetic field.

• Electric pulses are sent to the write head, and the resulting magnetic patterns are recorded on the disk below.

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Data Organization

• How it’s Done:

– This is basically fitting as much data as reasonably possible on a disk.

– The disk will have many tracks which are rings of space around the center.

– Data are transferred to and from the disk in sectors. Each track will have hundreds of sectors.

– Each adjacent track on a ring has a gap in between to avoid errors in reading each track.

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Data Organization

• Data disk layout:

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Formatting

• Prepares the disk for use.

• Formatting will embed the specifications of the disk on itself so it can be read effectively.

• Remember that the head won’t know where to start and end each track if it isn’t “told”.

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Physical Characteristics

• Head Motion:– Fixed Motion:

• One read-write head per track• Very rare today

– Movable Head:• One read-write head• Arm can be extended or retracted to position the

head

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Physical Characteristics

• Disk portability:– Nonremovable Disk:

• Permanently mounted in the disk drive• Example: hard disk in a personal computer

– Removable Disk:• Can be removed and replaced with another

one• Examples: floppy disks and ZIP cartridge disks

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Physical Characteristics

• Sides:– Double Sided:

• Magnetizable coating applied to both sides

– Single Sided:• Magnetizable coating only on one side• Less expensive than double sided

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Physical Characteristics

• Platters:– Single Platter:– Multiple Platters:

• Stacked vertically

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Physical Characteristics

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Physical Characteristics

• Movable head• One read-write head per platter surface• Heads have same distance from the center• Cylinder: set of all the tracks at equal distance

from the center of the disk– Reduction of head movement– Increase of speed (transfer rate)

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Physical Characteristics

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Physical Characteristics• Head Mechanism:

– Fixed gap • Read-write head has fixed distance above platter

– Contact (floppy)• There is physical contact with the medium during

the read or write operation• Small, flexible, and the cheapest of the disks

– Winchester• Heads in sealed drive, free of contaminants• Greater data density (closer to disk’s surface)

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Disk Performance Parameters

Diagram of a disk I/O transfer

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Disk Performance Parameters

• Track selection:– Movable-head system:

• Moving head– Fixed-head system:

• Electronically

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Disk Performance Parameters

• Total average access time:

Ta=Ts+(1/2r)+(b/rN)

Where r: rotation speed

b: number of bytes to be transferred N: number bytes of a track Ts: seek time

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Disk Performance Parameters

• Total average access time: Ta=Ts+(1/2r)+(b/rN)

– Access time: seek time plus rotational delay• Ts: average seek time (to position head at track)• Rotational delay: time to reach the head for the

beginning of the sector– Transfer time: data transfer (read or write)

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Disk Performance Parameters

• Conclusions:– Order of reading sectors is important to

I/O operations.• Sequential organization is faster than random

– The way of reading or writing multiple sectors can be controlled.

– There can be I/O requests competing for the same disk.

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Compact Disk

• Introduced in 1983• Low-cost disk storage technology• Six optical disk systems

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Optical Disk Products

• CD• CD-ROM• CD-R• CD-RW• DVD• DVD-R• DVD-RW

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ityCD-ROM

• Rugged• Error correction devices• Composition• Information retrieval• Pits and lands

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ityCD-ROM

Advantages/Disadvantages

• Inexpensive replication• Removable• Longer access time• Not capable of being updated

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ityCD-R

• Prepared differently• Information is recorded differently

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ityCD-RW

• Capability• Method• Process• Advantage/disadvantage

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ityDVD

• Replaced VHS analog video tape• Disk space• 3 major differences between CDs

A little history about your USB

Memory stick

Started with something like this….

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ityHISTORY

First commercial product • Trek Technology and IBM began selling

the first USB flash drives commercially in 2000.

• IBM marketed the first such drives in North America, with its product the "DiskOnKey" (which was manufactured by the Israeli company M-Systems).

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ity • IBM's USB flash drive became available December 15, 2000, and had a storage capacity of 8 MB, more than five times the capacity of the commonly used floppy disks.

Old 16MB IBM DiskOnKey flash drives.

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ity • In 2004 Trek Technology brought several lawsuits against other USB flash drive manufacturers and distributors in an attempt to assert its patent rights to the USB flash drive. A court in Singapore ordered competitors to cease selling similar products that would be covered by Trek's patent, but a court in the United Kingdom revoked one of Trek's patents in that country.

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Second Generation…

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ity • Modern flash drives have USB 2.0 connectivity.

• they do not currently use the full 480 Mb/s (60MB/s) the USB 2.0 Hi-Speed specification supports.

• The fastest drives currently available use a dual channel controller

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• overall file transfer speeds vary considerably, and should be checked before purchase.

• Speeds may be given in Mbyte per second, Mbit per second, or optical drive multipliers such as "180X”.

• Typical fast drives claim to read at up to 30 megabytes/s (MB/s) and write at about half that.

USB Memory Sticks’ Types and Varieties

Essential components

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ity • There are typically four parts to a flash drive:

• 1- Male type-A USB connector – provides an interface to the host computer.

• 2- USB mass storage controller – implements the USB host controller. The controller contains a small microcontroller with a small amount of on-chip ROM and RAM.

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ity • 3- NAND flash memory chip – stores data. NAND flash is typically also used in digital cameras.

• 4- Crystal oscillator – produces the device's main 12 MHz clock signal and controls the device's data output through a phase-locked loop.

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Additional components

• Jumpers and test pins.• Bunch of LEDs.• Write-protect switches.• Unpopulated space.• USB connector cover or cap.• Transport aid.• expandable storage via an internal

memory card slot.

Size and style of packaging

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Housing

• Some manufacturers differentiate their products by using elaborate housings.

• USB flash drives have been integrated into other commonly-carried items such as watches, pens, and even the Swiss Army Knife.

• others have been fitted with novelty cases such as toy cars or LEGO bricks.

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• Heavy or bulky flash drive packaging can make for unreliable operation when plugged directly into a USB port; this can be relieved by a USB extension cable.

Examples… =D

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ityUSB Flash Drive

• A USB flash drive consists of a NAND-type flash memory storage device integrated with a USB.

• Flash memory uses the advantage of recent advances in microprocessor technology.

• Memory is based on EPROM (Erasable Programmable Read-Only Memory) and EEPROM technologies.

• EEPROMs were developed that broke the erasure region into smaller sections.

• High-speed serial data interfaces made memory systems with serially accessed storage viable.

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ityUSB Flash Drive

• USB connector• USB mass storage

controller device• Test points• Flash Memory Chip• Crystal Oscillator• LED• Write-Protect Switch• Space for second flash

memory chip

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ityFile System

• Most flash drives ship preformatted with the FAT (File Allocation Table) or FAT 32 file system.

• FAT maintenance utilities can be used.

• Flash drives file system can be changed to that of the operating system.

• Flash drives can be defragmented, but this brings little advantage.

• Flash Drives can be partitioned.

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ityUses

• Personal data transport

• Application carriers

• Booting operating systems

• Audio players

• Backup

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ityAdvantages

• Flash drives are mechanically very robust.

• Compared to hard drives, flash drives use little power.

• Most modern operating systems can read and write to flash drives without installing drivers.

• Flash drives are resistant to a wide range of temperatures.

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ityDisadvantages

• Flash drives can sustain only a limited number of write and erase cycles.

• Most USB flash drives do not include a write-protect mechanism.

• Their small size makes it easy to misplace them.

• USB flash drives have a high price per unit of storage.

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Questions

1. What are the two main operations done with memory? 2. What two phenomena do magnetic disks make use of

to function? 3. According to disk portability, which are the two types

of disks?4. What are the two components of the access time?5. What are pits? Lands?6. What are the 6 optical disk products?

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Questions

7. Name one of the essential components of a flash drive

8. For the second generation of USB flash drives, what type of connectivity do they have?

9. What type of memory storage device is used in USB flash drives?

10. Memory on a USB Flash drive is based on what type of technology?

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Answers

1. Read and write2. Electricity and Magnetism3. Nonremovable disk and removable disk.4. The seek time and the rotational delay.5. Pits are digitally recorded information imprinted on

the surface of the disk. Lands are the areas between the pits

6. cd/cd-rom, cd-r, cd-rw, dvd, dvd-r, dvd-rw

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Answers

7. USB connector, mass storage controller device, test point, flash memory chip, crystal oscillator, LED

8. USB 2.0 connectivity9. NAND-type flash memory10. Electrically Erasable Programmable Read-Only

Memory (EEPROM).

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Bibliography

• www.wikipedia.com• www.howstuffworks.com• www.cs.jhu.edu• www.computerhope.com• www.articlesbase.com