Secondary Storage Input Output Processing Internal Memory

Secondary Storage used to permanently store data and programs

Physical Parts l storage device –diskette drive –hard-disk drive –optical disk drive –tape drive l storage medium –magnetic disks, tapes –optical disks

Magnetic Disks l disks covered with a thin layer of ferrous oxide l data is stored as magnetized fields on the disk l most widely used secondary storage medium l diskettes, zip disks, jaz disks, superdisks, hard disks

Diskettes l flexible plastic disks encased in a plastic jacket l sizes: –3 1 / 2 inch –5 1 / 4 inch l densities: –low or double density –high density

Diskette data storage l data are stored and accessed at a unique disk address l formatting a diskette divides it into addressable storage locations –tracks –sectors –file directory (file allocation table)

The Surface of a Disk l Track l Sector l Cluster

Disk Drive l rotates the disk l a read/write head accesses the tracks through the recording window –direct access device l disk drives are specific to the size and density of the diskettes

Uses for Diskettes l transferring small amounts of data between computers l doing small amounts of backup l software distribution l Other considerations: –very portable –comparatively slow access to data –inexpensive –diskettes are subject to damage

Hard Disks l metal disks (platters) covered with ferrous oxide l 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.) l direct access device l fast data access l large storage capacity –4 to 36 gigabytes or more l Smart 2 Ultra ATA/66

Zip Drives and Disks l internal or external drive l stores: –100 MB on a single disk –250 MB l reasonable cost

Jaz Drives and Disks l stores 1 or 2 GB per disk l internal or external l fast access to data

Imation LS-120 Super Disk Drive and SuperDisks Diskettes l SuperDisks store 120 MB of data l SuperDisk Drive reads and writes both the SuperDisk diskette and conventional MB diskette

Magnetic Tape l data is stored on a mylar tape coated with ferrous oxide l typically used to backup file servers l sequential access l common types: –4mm/8mm DAT tapes –DDS –DLT tapes

Optical Storage Media l data is stored by burning tiny holes in the surface of a optical disk with a laser beam l very large storage capacity (several GB of data on a optical disk) l media of choice for software distribution l good for storing multimedia data

Types l CD-ROMS –most common –used extensively for software distribution –access times dependent on the speed of the CD- ROM disk drive (24x, 32x, 40x) l CD-R l CD-RW –8x4x20x means 8x record, 4x rewrite, 20x read l DVD

Factors to consider when comparing types of storage: l Internal vs. external design l media capacity l portability l access to data –speed –read/write capability –type (sequential or direct) l cost

Disk Controllers l IDE, EIDE, Ultra IDE l SCSI, SCSI wide, SCSI ultrawide, Ultra 2 SCSI