Exploring the Digital DomainExploring the Digital Domain

Secondary Memory and Input/Output

Input/Output– exchanging data and instructions between the

user and the computer Secondary Storage

– auxiliary storage for data and instructions

I/O Subsystem

backup or alternative storage in place of (volatile) RAM

cheaper, mass storage for long term use secondary memory devices (and

media) are distinguished by their capacities, speed, and cost

Secondary Memory (Storage)

RANDOM ACCESS– items are independently addressed

– access time is constant

DIRECT ACCESS– items are independently addressed in regions

– access time is variable—though not significantly

SEQUENTIAL ACCESS– items are organized in sequence (linearly)

– access time is significantly variable

Types of Memory Access

SEQUENTIAL ACCESS STORAGE DEVICES AND MEDIA (SASD)– magnetic tape

DIRECT ACCESS STORAGE DEVICES AND MEDIA (DASD)– magnetic floppy disks– magnetic hard disks– optical discs

Secondary Memory

Memory Hierarchy I

Memory Hierarchy II

stores data represented by magnetized particles in linear tracks

magnetized clusters or domains are aligned to represent binary codes

Magnetic Tape

Magnetic Tape

LONGITUDINAL– older format used for record-keeping

SERPENTINE– used for system backups

HELICAL SCAN– high capacity formulation used for system

backups and archives

Magnetic Tape Formats

Longitudinal (9-track)

Serpentine (QIC)

magnetic hard and floppy disks removable hard disks optical discs

– CD-ROM, CD-R,– WORM,– magneto-optical

GEOMETRY: TRACKS and SECTORSGEOMETRY: TRACKS and SECTORS

Direct Access Storage Devices

CAV — constant angular velocity (e.g., floppy and hard disks)

CLV — constant linear velocity (e.g., optical discs)

Zoned CAV — number of sectors depends upon zone

DASD Media

SEEK — controller advances read/write head to proper track

LATENCY — waits for proper sector to rotate under head

READ/WRITE — disk head scans the sector for read or write

Direct Access

FLOPPY DISKS– 5.25 and 3.5 inch

diskettes

– 1.44 – 2.88 MBytes capacity

– access: drive speeds – 600 r.p.m.

– inexpensive, archival uses for small amounts of data

HARD DISKS– 3.5 inch has approx

3,000 tracks per side

– multiple disk, sides (cylinders)

– high capacity

– access: drive speeds – 3,600 up to 7,200 r.p.m.

– on-line storage

Magnetic Disks

data is stored in blocks

blocks occupy sectors sectors on tracks files have names files are indefinite in

size files may be updated

(in part or whole)

Disk vs. File Organization

Compact Disc–Read Only Memory (CD-ROM)– archived and published information– high capacity

Compact Disc–Recordable (CD-R)– recordable– readable using CD-ROM technology

Write Once, Read Many (WORM)– high capacity archival storage

Magneto-Optical Discs– erasable, high capacity, on-line storage alternative

Digital Versatile Discs (DVD)– Very high capacity, read-only storages

Optical Discs

based on CDDA technology CLV geometry density: 16,000 tpi up to 650 MBytes nonerasable, nonwriteable

storage discs are mastered, pressed

(mass production) multispeeds drives common

CD-ROM

discs are “burnt” one at a time

high intensity laser beam used for recording pregrooved tracks

low intensity beam for reading

attributes similar to CD-ROM

CD–R

Magneto-Optical– combines magnetic and optical technologies

– erasable, readable-writable storage

– very high capacity

– not yet economical

Digital Versatile Disc (DVD)– successor to CD-ROM technology

– very high capacity read-only storage

– multiple disc, multiple sided storage

Other Optical Media

keyboard mouse scanners (flatbed, slide, and drum) digital cameras sound digitizers MIDI (Musical Instrument Digital Interface) Video digitizers

Input Peripherals

video display monitors– monochrome and color– CRT and LCD

Output Peripherals

cathode ray tube (CRT)

phosphors excited by electron gun beams

RGB composite color horizontal scanning

pattern to refresh phosphors

CRT technology

video display monitors– monochrome and color– CRT and LCD

printers– character, line, and page

Output Peripherals

CHARACTER dot matrix

– low-cost, text and graphic printers

– slow-speed, low quality

inkjet– medium-priced

– general-purpose

PAGE laser printers

– high-quality

– assortment of sizes, performance, and cost

Printers

video display monitors– monochrome and color– CRT and LCD

printers– character, line, and page

sound and voice output MIDI synthesizers

Output Peripherals