Secondary Storage

Input Output

Processing

InternalMemory

Secondary Storage

used to permanently store data and programs

Physical Parts storage device

– diskette drive– hard-disk drive– optical disk drive– tape drive

storage medium– magnetic disks, tapes– optical disks

Magnetic Disks

disks covered with a thin layer of ferrous oxide

data is stored as magnetized fields on the disk

most widely used secondary storage medium

diskettes, zip disks, jaz disks, superdisks, hard disks

Diskettes flexible plastic disks encased in a

plastic jacket sizes:

– 3 1/2 inch

– 5 1/4 inch

densities:– low or double density– high density

Diskette data storage

data are stored and accessed at a unique disk address

formatting a diskette divides it into addressable storage locations– tracks– sectors– file directory (file allocation table)

The Surface of a Disk

Track Sector Cluster

Disk Drive rotates the disk a read/write head accesses the

tracks through the recording window– direct access device

disk drives are specific to the size and density of the diskettes

Uses for Diskettes transferring small amounts of data

between computers doing small amounts of backup software distribution Other considerations:

– very portable– comparatively slow access to data – inexpensive– diskettes are subject to damage

Hard Disks

metal disks (platters) covered with ferrous oxide

disk pack– set of disks on a mounting shaft– access mechanism containing the

read/write heads– circuit board – sealed in an airtight unit

Hard Disks (cont.)

direct access device fast data access large storage capacity

– 4 to 36 gigabytes or more Smart 2 Ultra ATA/66

Zip Drives and Disks

internal or external drive stores:

– 100 MB on a single disk– 250 MB

reasonable cost

Jaz Drives and Disks

stores 1 or 2 GB per disk internal or external fast access to data

Imation LS-120 Super Disk Drive and SuperDisks Diskettes SuperDisks store 120 MB of data SuperDisk Drive reads and writes

both the SuperDisk diskette and conventional 3.5” 1.44 MB diskette

Magnetic Tape

data is stored on a mylar tape coated with ferrous oxide

typically used to backup file servers sequential access common types:

– 4mm/8mm DAT tapes– DDS– DLT tapes

Optical Storage Media

data is stored by burning tiny holes in the surface of a optical disk with a laser beam

very large storage capacity (several GB of data on a optical disk)

media of choice for software distribution

good for storing multimedia data

Types

CD-ROMS– most common– used extensively for software distribution – access times dependent on the speed of the

CD-ROM disk drive (24x, 32x, 40x) CD-R CD-RW

– 8x4x20x means 8x record, 4x rewrite, 20x read

DVD

Factors to consider when comparing types of storage: Internal vs. external design media capacity portability access to data

– speed– read/write capability– type (sequential or direct)

cost

Disk Controllers

IDE, EIDE, Ultra IDE SCSI, SCSI wide, SCSI ultrawide,

Ultra 2 SCSI