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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
stores data represented by magnetized particles in linear tracks
magnetized clusters or domains are aligned to represent binary codes
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
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
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