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Storage Devices

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e.g. floppy disks, hard disks and removable disk cartridge. Floppy Disk ... usually cartridge tape. serves as a primary means of. backup, ... – PowerPoint PPT presentation

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Title: Storage Devices


1
Storage Devices
2
Storage Devices
  • Also called secondary storage
  • store data programs permanently for future use
  • can be used as both input output devices

3
Magnetic Disk Storage
  • Most widely used storage medium
  • consists of a round piece of plastic or metal,
    the surface on which is covered by a magnetic
    materials.
  • e.g. floppy disks, hard disks and removable disk
    cartridge

4
Floppy Disk
  • Random-access storage medium
  • provides storage of 1.44MB data
  • A circular piece of thin plastic that is coated
    with magnetic material
  • the circular piece of plastic is enclosed by a
    rigid plastic shell
  • Formatting prepares a floppy disk for storage by
    defining the tracks, cylinders, and sectors on
    the disk surface
  • time required to locate data and transfer it to
    memory is called the access time.

5
Data is recorded on disk in concentric circular
bands called tracks. The tracks on a disk are
similar to the grooves on a phonograph record.
Each track is divided into pie-shaped wedges
called sectors. Two or more sectors combine to
form a cluster.
6
Most computers maintain on the disk a table with
the sector and track locations of data. This
table, the file allocation table (FAT), enables
the computer to locate data easily.
7
Structure of a Floppy Disk
8
Hard Disks
  • Fixed in the System Unit
  • Consists of one or more rigid platters coated
    with a magnetic material
  • the platters, read/write heads, and the access
    arms that move the heads across the disk surface
    are all enclosed in an airtight, sealed case

9
  • Access time for a hard disk is significantly less
    than that for a floppy disk because a hard disk
    spins faster and unlike a floppy disk, a hard
    disk is spinning constantly (7200 revolutions per
    minute).
  • hard disks are permanently encased within the
    disk drive in a sealed environment free from dust
    and dirt. The disk can spin very rapidly, with
    the read/write head "floating" above the disk's
    surface.

10
Hard Disk Interfaces
  • To connect a hard disk to a microcomputer
    motherboard, you must have a hard disk interface.
  • This component includes circuitry that conforms
    to a standard recognized by both the hard disk
    and the motherboard manufacturer.
  • Common standards are Integrated Drive Electronics
    (IDE) and Small Computer System Interface (SCSI).

11
Removable Disks
  • Provide both the storage capacity and fact access
    time of hard disk and the probability of floppy
    disks.
  • Examples
  • Iomegas ZIP (100MB/250MB)
  • JAZ (1-2 GB)
  • Imations Superdisk (120MB)

12
Maintaining Stored Data
  • To prevent loss of data, 2 procedures should be
    performed regularly
  • Backup
  • process of creating a copy of important programs
    and data
  • Defragmentation
  • process of reorganizing data stored on a disk so
    that files are located in contiguous (adjacent)
    clusters.

13
DVD/CD-ROM and Optical Disks
  • By using laser technology, optical disk can store
    large quantities of data
  • a high power laser writes data on an optical disk
    by burning microscopic holes on the disk surface
  • a lower power laser reads the data by reflecting
    light off the disk surface. The reflected light
    is converted into a series of bits

14
  • DVD/CD-ROM
  • DVD/CD-Read Only Memory
  • can store 650 MB data
  • suitable for reference material such as
    encyclopedias, catalogs and pictures
  • DVD/CD-R
  • CD-Recordable
  • write once, read many
  • DVD/CD-RW
  • DVD/CD-Rewritable
  • erasable write many, read many
  • MO
  • Magneto-Optical
  • Floptical (Optical Magnetic)

15
Magnetic Tape
  • Consists of a thin ribbon of plastic, one side of
    which is coated with a material that can be
    magnetized to record binary data.
  • A sequential storage media (must write and read
    records on after another)
  • usually cartridge tape
  • serves as a primary means of
  • backup,
  • a method of transferring data between system, and
  • a cost-effective way to store data that does not
    have to be accessed immediately

16
Other types of Storage Devices
  • PC Cards (PCMCIA)
  • Flash Memory Card
  • Memory Stick
  • Smart Card
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