Overview – Meaning and Definition of Computer Memory Unit, types
of storage devices, meaning of primary storage/primary storage devices/ random
access memory/ secondary storage devices/ floppy disc drive/ hard drive/
magnetic tape/ diskettes/ compact disc/ digital versatile disc and USB flesh
drives
Computer Memory Unit:
What is Memory
Unit of Computer?
A
data storage device is a device for recording (storing) information
(data). Recording can be
done using virtually
any form of energy, spanning from manual muscle power
in handwriting, to acoustic vibrations in phonographic recording, to
electromagnetic energy modulating magnetic tape and optical discs.A storage
device is a hardware device capable of storing information. There are two types of storage devices used in
computers; a primary storage device such as computer RAM and a secondary
storage device such as a computer hard disk drive.
Hierarchy
of Storage:
Types and
Classification of Storage Devices:
Primary
Storage :- (Meaning of Primary Storage) - Primary storage (or main memory or internal
memory), often referred to simply as memory, is the only one directly
accessible to the CPU. The CPU continuously reads instructions stored there and
executes them as required. Any data actively operated on is also stored there
in uniform manner.
Primary Storage
Device :-
Also known as internal memory and main memory, primary storage is a storage
location that holds memory for short periods of times while the computer is on.
For example, computer RAM and cache are both examples of a primary storage
device. This type of storage is the fastest type of memory in your computer and
is used to store data while it's being used. For example, when you open a
program data is moved from the secondary storage into the primary storage.
Random Access
Memory :-
RAM, also known as main memory or system memory, is a term commonly used to
describe the memory within a computer.Unlike ROM, RAM is a volatile memory and
requires power; if power is lost, all data is also lost. Below is an example
image of a 512MB DIMM memory stick.Over the evolution of computers there has
been several different types of RAM used in computer. Some of the more common
examples are: DIMM, RIMM, SIMM, SO-DIMM, and SOO-RIMM.
Secondary
storage device:- Also known as external memory and auxiliary storage, secondary
storage is a storage medium that holds information until it is deleted or
overwritten regardless if the computer has power. For example, a floppy disk
drive and hard disk drive are both good examples of secondary storage devices.
As can be seen by the below picture there are three different types of storage on a computer,
although primary storage is accessed much faster than secondary storage because
of the price and size limitations secondary storage is used with today's
computers to store all your programs and your personal data. Finally , although
off-line storage could be considered secondary storage, we've separated these
into their own category because these types of media can be easily removed from
the computer and stored elsewhere. Some other examples of secondary storage
technologies are: flash memory (e.g. USB flash drives or keys), floppy disks,
magnetic tape, paper tape, punched cards, standalone RAM disks, and Iomega Zip
drives.
Floppy Disk
Drive :-
A Floppy Disk Drive, or FDD for short, is a computer disk drive that enables a
user to easily save data to removable diskettes. Although 8" disk drives
made available in 1971 were the first real disk drives, the first widely used
an floppy disk drives were the 5 1/4" floppy disk drives, which were later
replaced with 3 1/2" floppy disk drives. However, today because of the
limited capacity and eliability of floppy diskettes many computers no longer
come equipped with floppy disk drives and are being replaced with CD-R and
other writable disc drives and flash drives.
Above
is an example of each of the floppy drives.
Hard drive :-The
computer's main storage media device used to permanently store all data on the computer. Also referred
to as a hard disk drive or abbreviated as HD or HDD, the hard drive was first
introduced on September 13, 1956 and consists of one or more hard disk platters
inside of air sealed casing. Most hard drives are permanently stored in an
internal drive bay at the front of the computer and are connected with either
ATA, SCSI, or a SATA cable and power cable. Below is an illustration of the
inside of a hard disk drive.
Magnetic tape
:-
Magnetic tape is a medium for magnetic recording, made of a thin magnetizable
coating on a long, narrow strip of plastic. It was developed in Germany, based
on magnetic wire recording. Devices that record and play back audio and video
using magnetic tape are tape recorders and video tape recorders. A device that
stores computer data on magnetic tape is a tape
drive. Magnetic tape revolutionized broadcast and recording. When all
radio was live, it allowed programming to be prerecorded. At a time when gramophone records were recorded in one take,
it allowed recordings in multiple parts, which mixed and edited with tolerable
loss in quality. It is a key technology in early computer development, allowing
unparalleled amounts of data to be mechanically created, stored for long
periods, and to be rapidly accessed.
Diskettes :- You can use
the diskette to store small amounts of information. According to
Mediastoragedevices.com, a widely used diskette has a capacity of 1.44 Mb. It
records data as magnetized spots on tracks on its surface. Diskettes are
portable, allowing you to move data from one computer to another. You have to
ensure that you do not store data on the diskette for long periods, because as
the magnetic field weakens, you risk losing your stored data.
Compact Disc:- Stands for
"Compact Disc." CDs are circular discs that are 4.75 in (12 cm) in
diameter. The CD standard was proposed by Sony and Philips in 1980 and the
technology was introduced to the U.S. market in 1983. CDs can hold up to 700 MB
of data or 80 minutes of audio. The data on a CD is stored as small notches on
the disc and is read by a laser from an optical drive. The drives translate the
notches (which represent 1's and 0's) into usable data. The first CDs were
audio CDs, which eventually replaced audio tapes (which earlier replaced
records). Audio CDs have the advantage of allowing the user to jump to
different places on the disc. CDs can also be
listened
to an unlimited number of times without losing quality. Audio tapes can start
to lose quality after listening to them as few as ten times. This is because
the laser that reads the data on a CD doesn't put pressure on the disc, whereas
the play heads on a tape deck slowly wear away the magnetic strip on the tape.
Digital
Versatile Disc :-
Stands for "Digital Versatile Disc." It can also stand for
"Digital Video Disc," but with the mulitple uses of DVDs, the term
"Digital Versatile Disc" is more correct. Yep, the technology naming
people just love to confuse us. A DVD is a high-capacity optical disc that
looks like a CD, but can store much more information. While a CD can store 650
to 700 MB of data, a single-layer, single-sided DVD can store 4.7 GB of data.
This enables massive computer applications and full-length movies to be stored
on a single DVD. The advanced DVD formats are even more amazing. There is a
twolayer standard that doubles the single-sided capacity to 8.5 GB. These disks
can also be double-sided, ramping up the maximum storage on a single disc to 17
GB. That's 26 times more data than a CD can hold! To be able to read DVDs in
your computer you'll need a DVD-ROM drive. Fortunately, DVD players can also
read CDs. To play DVD movies on your computer, you'll need to have a graphics
card with a DVD-decoder, which most computers now have.
USB Flash
Drives:-
The convenience of storing and transferring data in a device that is portable
and has a large capacity comes with the USB flash drive. You only have to
connect it to the computer through the USB port and transfer data from the
computer to the flash drive and vice versa. It comes in various sizes (usually
in gigabytes) to suit your usage needs and you can carry it in your pocket or
wallet or on your key chain. Apart from being fast in uploading data, it also
gives you the option of modifying the stored data by either erasing or
rewriting according to your requirements.
Short
exam hand made lecture notes of computer ICT practical file basics and Computer
storage devices lecture notes
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