Ch-4 Storage Device

BIT

Short for binary digit. The smallest unit of information handled by a computer. One bit expresses 1 or 0 in a binary numeral.. A group of 4 bits make a Nibble and group of 8 bits makes up a Byte.

BYTE

Short for binary term. A unit of data, today almost always consisting of 8 bits. A byte can represent a single character, such as a letter, a digit, or a punctuation mark. Because a byte represents only a small amount of information, amounts of computer memory and storage are usually given in kilobytes (1,024 bytes), megabytes (1,048,576 bytes), or gigabytes (1,073,741,824 bytes).

WORD
The native unit of storage on a particular machine. A word is the largest amount of data that can be handled by the microprocessor in one operation and also, as a rule, the width of the main data bus. Normally Word sizes of are 8 bits, 16 bits , 32 bits & 64 bits are the most common. The computer speed depends on the size of word.

What is meant by computer storage? How will you classify it?

The place or location where computer store data or information for permanent or temporary basis
is called memory.

There are two main types of memory.
1. Main memory / Primary memory
2. Secondary memory / Auxiliary memory / Backing storage.

Main memory / Primary memory
This type of memory is the internal memory of computer i.e. RAM & ROM.
The speed of this memory is high because that is direct connected with processor

Secondary memory / Auxiliary memory / Backing storage.
It is also important type of memory. The speed of this memory is slow to compare with main memory. But this type of memory has some main futures i.e. store large amount of data, run operating system, store application programs etc. the examples of this type are hard disk, Floppy disk, Compact Disk , magnetic tap etc.

ROM (Read Only Memory)
ROM is a main part of computer; it is non-volatile memory because the information, which store in ROM is not erase or delete. Basically ROM has four main features i.e.

a. Check input output device in booting time
b. Have information about computer configuration.
c. Load operating system.
d. Receive signals from keyboard.

ROM has also two types PROM & EPROM
PROM (Programmable Read Only Memory) PROM is a ROM where the user can load the data or information of the ROM and can modify it.

EPROM (Erasable Programmable Read Only Memory). It is another type of ROM, which erase or delete the current program or data from ROM for further modification.

RAM (Random Access Memory)
RAM is type of main memory, it is a small chip, which fixed on mother board. It is temporary memory which store data and information still to computer switch on. The data and information store and retrieve randomly on RAM. RAM takes data from hard disk, send to processor for processing, and as also send back to hard disk for permanent saving. As computer speed depend on the size of RAM as much as the size of RAM increased the speed of the computer will be fast. RAM also available in size of 32mb, 64mb, 128mb, 256mb and 512mb etc.





SIMM (Single In Line Memory Module)
SIMM is an advance form of RAM, SIMM is a small chip, which have module on single side of the chip SIMM transfer data in 32 bits size of word. We can use more than one SIMM chip on motherboard.

DIMM (Double In Line Memory Module)
DIMM is also type of the RAM, which double in size to compare with SIMM. DIMM have module chips on both sides, and also transfer data in 64 bits as the speed of the DIMM more than SIMM, because SIMM transfer data in 32 bits. As we can use more than one DIMM chip on motherboard.

Q.4 What is Sequential storage and Direct Access storage devices?

Ans. Sequential storage and Direct Access storage devices are the types of Secondary memory. Both types of devices are used for backup and other purposes.

Sequential Access Storage/ Magnetic Tape
In these devices data are store sequentially, each record store one after another and there is no spaces among the records or files. For example we have 100 records in Sequential device, and we want to access record no 75, as computer will start searching from record no 1 to 74 then find desired record. As in sequential storage device processing is slow. Example of sequential storage device is magnetic tape. Sequential devices are used only for backup purposes.

Direct Access Storage / Magnetic Disk
These types of devices read and write record or file directly by the help of their own addresses, in direct storage devices records are store randomly there is no sequence among files and records, each record or file have a specific code (address), which is used for identification of the file or record. Direct Access devices processing are fast than sequentially devices. Examples of direct access devices are hard disk, floppy disk and CDs.

Write short notes on Floppy disk, Hard disk and CD-Rom.

Floppy Disk
Floppy disk is a secondary storage Input/output device, which store data randomly. A floppy disk divided into circles or tracks and each track divided into sectors, the data store on sectors. There is a head in floppy drive that read and write the data. Now a day floppy disk usually used for transferring data from one computer to another. Floppy disks are available in of 3.5 and 5.25 inches. The capacity of 3.5 inch floppy is about 1.44 MB.

Hard Disk
Hard disk is type of secondary storage device, which store and retrieve data randomly. Hard disk function similar to floppy disk, but hard disk is fixed in computer and also have large amount of capacity. Normally harddisk is used to have operating system and other application programs like DOS, WINDOWS, Ms-Office, Programming languages, Games etc. Now a day the hard disks available in size of from 1 GB to 120GB. A large capacity harddisk can be divided into several partitions.

CD-ROM (Compact Disk Read Only Memory)
It is also a secondary storage device, which used everywhere with computers.
A compact disc is a nonmagnetic, polished metal disc with a protective plastic coating that can hold up to 74 minutes of high-fidelity recorded sound. A normal size CD can store 600 books of 500 pages. The disk is read by an optical scanning mechanism that uses a high-intensity light source. It is a less expensive device that used everywhere for different purposes.


**********