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Secondary Storage

Processing. Input. Output. Internal Memory. Secondary Storage. 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.

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Secondary Storage

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  1. Processing Input Output Internal Memory Secondary Storage

  2. Secondary Storage used to permanently store data and programs

  3. Physical Parts • storage device • diskette drive • hard-disk drive • optical disk drive • tape drive • storage medium • magnetic disks, tapes • optical disks

  4. 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

  5. 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

  6. 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)

  7. The Surface of a Disk • Track • Sector • Cluster

  8. 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

  9. 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

  10. 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

  11. Hard Disks (cont.) • direct access device • fast data access • large storage capacity • 4 to 36 gigabytes or more • Smart 2 Ultra ATA/66

  12. Zip Drives and Disks • internal or external drive • stores: • 100 MB on a single disk • 250 MB • reasonable cost

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

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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

  19. Disk Controllers • IDE, EIDE, Ultra IDE • SCSI, SCSI wide, SCSI ultrawide, Ultra 2 SCSI

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