SEB070023-TUTORIAL 5

Magnetic Disk

Description:
On magnetic disks, data is encoded as
microscopic magnetized needles on the disk's surface. Data can be record and
erase on a magnetic disk any number of times, just as with a cassette

tape.

Advantage:
Although the variance in DASD access times
isn’t as wide as with magnetic tape, the location of the specific record still
has a direct effect on the amount of time required to access it.

Fixed-Head Magnetic disk

Looks like a
large CD or DVD covered with magnetic film.

Formatted,
usually on both sides, into tracks. Data is
recorded serially on each track by the fixed read/write head positioned
over it

Advantage:

·
Faster than the movable –head disks

·
These devices are used when speed
is of the utmost importance such as spacecraft monitoring or aircraft
application

Movable-Head Magnetic
Disk Storage

Have one
read/write head that floats
over the surface of each disk. It
can be a single platter.
It can be a part
of a disk pack (stack
of platters)

Examples:

Floppy disk :

A typical 5¼-inch floppy
disk can hold 360K or 1.2MB (megabytes).
3½-inch floppies normally

store 720K, 1.2MB or 1.44MB of data.

Hard
disk :

Hard disks can store
anywhere from 20MB to more than 200GB. Hard disks are also from 10 to 100 times
faster than floppy disks.

Removable
cartridge : Removable cartridges are hard disks encased in a metal or
plastic

cartridge, so you can remove them
just like a floppy disk. Removable cartridges are very fast, though usually not
as fast as fixed hard disks

Optical Disk

Description:
An optical disc is an electronic data storage medium that can be written to and
read using a low-powered laser beam.

Advantage:
· An optical disc holds much more data.

· The greater control and focus possible with laser beams (in
comparison to tiny magnetic heads) means that more data can be written into a
smaller space.

· Storage capacity increases with each new generation of optical
media.

· Emerging standards, such as Blu-ray, offer up to 27 gigabytes (GB) on a single-sided 12-centimeter disc. In comparison, a diskette, for example, can hold 1.44 megabytes (MB).

·Optical discs are inexpensive to manufacture and data stored on them is relatively impervious to most environmental threats, such as power surges, or magnetic disturbances.

Examples:

CD-ROM

Like audio CDs, CD-ROMs come with data already encoded onto them. The data is permanent and can be read any number of times, but CD-ROMs cannot be modified.

CD-Rewritable

Data can be written, changed, and erased using phase change technology

DVD technology

DVD-ROMs can store more data, are smaller, and the spiral is wound tighter than CD ROMs

CD-RW

Offers the advantages of a DVD-ROM drive and a
CD-RW drive in a single unit that ca play DVD movies and audio CDs

Blu-rays

Flash Memory

Description:
Removable medium that emulates random access memory

Advantage:
· Flash drives are impervious to scratches and dust, and mechanically very robust making them suitable for transporting data from place to place and keeping it readily at hand.

·
Allow user to store data on
microchip card and move it from device to device as they would magnetic or
optical storage media.Data
are store securely even its removed from its power source.

Examples:

Pen drive

Memory card

Magneto-Optical Disks

Description:

It combines the technology of magnetic disks with that of optical discs. A kind
of

optical disc drive capable of
writing and rewriting data upon a magneto-optical disc.

Advantage:

·
MO disks can store up to several GB
of data and their access rate is faster than that of a floppy disk but slower
than that of hard drives.

·
These disks are hardier than
optical discs.Unlike
a CD, this process does not cause a physical change to the disk and because the
change is not permanent, changes can be made many times

Examples:

CD-ROMs