There are two basic forms of
storage devices: primary storage and secondary
storage. Primary storage or main storage can be compared to our brain where data or information can be stored. Secondary storage or alternative storage can be compared to a classroom notebook where data or information from the brain can be permanently stored.
THE COMPUTER'S MEMORY
Computer memory is also called
main storage, primary storage, primary
memory, internal storage, and main memory.
Primary storage or memory store data, results and instructions only temporarily. The memory is able to store data items only while the computer is turned on. Data items are destroyed when the compuyter is turned off.
The Types of Memory
Memory comes in two types: the Random Access Memory or RAM and the
Read-Only Memory or ROM. The RAM chip is volatile; while the ROM chip is
non-volatile. Data residing in the RAM can be read and altered. Data residing in
the ROM can only be read.
THE PRIMARY STORAGE HARDWARE
storage is made up of very thin wires that form circuits. These
are put together in a board and enclosed in a casing, which is called memory chip.
Memory chips can be installed together in a memory card called Single Inline
Memory Module or SIMM to increase a computer's memory capacity.
The Primary Storage Capacity
storage capacity is expressed in kilobytes. One (1) kilobyte is
equivalent to 1,024 bytes. It can also be expressed in megabytes. One (1)
megabyte is approximately one million bytes.
Accessing Data in the Memory
Data transfer is the tiume involved when transfer of data from the disk to the memory or another secondary storage device occurs. Data on a disk are read in a direct or random manner. Disks are also called Direct Access Storage Device or DASD.
The Magentic Tape
tape is made of polyester coated with magnetic material on one side.
The tape is wound on a reel or a cartridge. The amount of data that can
be sotred on a magnetic tape is expressed in terms of density, which is
equivalent to the number of characters per inch or bytes per inch (bpi).
The storage capaciuty of a tape is equal to the density times the length
of the tape in inches.
Data Storage on a Tape. The magnetic tape has nine tracks of recording
surfaces. Data are representedas a 1 bit and 0 bit.
Accessing Data on a Tape.
The tape drive or unit reads or writes data on a
tape. The magnetic tape unit has two reels on wehich the tape is mounted. One is called the supply reel and the other is called the take-up reel. The supply reel
contains the tape on which data will be recorded or read. The take-up reel is a
Data on a tape are read or written
in a sequential manner, which is slower than
that of the direct access manner.
THE SECONDARY STORAGE
storage is a permanent storage. It is convenient, reliable and
an inexpensive way of storing data, programs and information.
Benefits of Secondary Storage
storage is economical, reliable and convenient. All types of
secondary storage possess these benefits. However, some types are better than
Types of Secondary Storage
on the type of ,material used, the two classifications of secondary
storage devices are the paper and the magnetic devices. The paper storage devices include the punched card and the paper tape. The magnetic storage devices include the disk and the tape.
THE MAGNETIC STORAGE DEVICES
The Magnetic Disk
disk is the most commonly used type of magnetic storage
device. Magnetic disks come in two kinds: the hard disk and the floppy disk. Hard disk comes in three sizes, the 8-, 5 1/4- and 3 1/2-inch. the hard disk can hold up to 769 MB. The floppy disk comes in two sizes, the 5 1/4 and 3 1/2 inches. They can hold from 360 KB to 1.4 MB data.
The Disk Drive
and instructionss are stored on and retrieved from a disk by means of a
machine called a disk drive. Hard disk drives store data and instructions on a hard disk. Floppy disk drives store data and instructions on removable floppy disks. Both drives possess an access mechanism that read or writes data.
Data Storage on a Disk.
The surface of a disk is made up of concentric circles
called tracks where data are recorded as magnetic spots. Each track carries the
same amount of data with each track having a unique address numbered through
Accessing Data on a Disk.
There are four factors by which data are accessed
from a disk. Seek time is the time involved for the access arm of the disk drive to
position itself on the correct track. Head switching is the time by which the
read/write head is activated over a particular track. Rotational delay pertains to the time by which the head waits for the disk to spin to the actual data to be read.