What are Storing Devices of Computer and Explain the various types of storage devices of computer – Learn Computer Online Free

What are Storing Devices of Computer and Explain the various types of storage devices of computer – Learn Computer Online Free


Meaning of Storing Devices of Computer -

The data and instructions that are entered into the computer system through input units have to be Stored inside the computer before the actual processing starts. For storing computer uses its memory.

Computer memory is divided into –

(A) Primary or Main memory
(B) Secondary or Backing storage




1. Meaning of Primary or Main memory -Main memory of a computer is a general term for any type of computer memory other than backing storage (Secondary Storage devices). It consists of a number of storage locations, each storage location can hold a quantity of data called a word. A word is the number of bits that can be processed by the CPU in a single operation.

Types of main memory -
Main memory consists of Random Access Memory (RAM) and Read Only Memory (ROM)

1. Random Access Memory
Random Access Memory is a type of computer memory which holds its data as long as the computer is switched on. When the computer is switched off, any data held in RAM is lost. RAM is volatile memory. Data held in RAM can be read or written to by the CPU in any order. The purpose of random access memory is to hold the computer’s programs and data while they are being processed.

2. Read only Memory
Read only memory is a type of computer memory that holds its data permanently. Data held in ROM Can be read by the CPU in any order. ROM is therefore another type of direct access medium. The Contents of ROM are fixed when the computer is manufactured. In many microcomputer, read only Memory is used to hold part of the operating system program, the bootstrap loader, which is used to Help start up the computer. ROM has an access time of between 10 and 50 nanoseconds.

Storage Units of storing computer data:
Computers use the binary system because it is easy to represent the two states ‘on’ and ‘off’ inside a computer. These two states are represented by voltages. 0 (Zero) volts is used to represent 0 , and a voltage usually between 1 and 5 volts depending upon the types of computer , is used to represent 1. Computer uses different units to store data. The relationship between the different units is given below:
4 Bits = 1 Nibble
8 Bits = 1 Byte
1024 Bytes = 1 Kilobyte (KB)
1024 KBs = 1 Megabyte (MB)
1024 MBs = 1 Gigabyte (GB)
1024 GBs = 1 Terabyte (TB)


2. Secondary Memory - Secondary Memory is used as permanent storage for programs and data in a computer system. Backing storage is also called secondary storage or mass storage.

The following backing storage media are included in this unit:
1. Magnetic
2. Optical
3. Magneto-Optical (MO)
4. Digital Audio Tape (DAT)

Magnetic Hard disks
A hard disk (commonly known as a HDD (hard disk drive) or hard drive (HD) and formerly known as a fixed disk) is a non-volatile storage device which stores digitally encoded data on rapidly rotating platters with magnetic surfaces.

Optical
Optical storage media includes CD-ROM (Compact Disk –Read Only Memory), CD-R (Compact Disk Recordable), CD-RW (Compact Disk Rewritable), together with DVD-ROM (Digital Versatile Disk), DVDVideo, DVD-Audio, DVD-R (Digital Versatile Disk Recordable) and DVD-RAM.

CD-ROM (Compact Disk- Read Only Memory)
A CD-ROM is 120 mm in diameter and 1.2 mm thick. When a CD-ROM is made, the data is moulded into tiny holes called pits on the clear plastic disk. The plastic disk is then coated with a reflective aluminum Layer and then a protective lacquer. The pits are arranged in a spiral starting in the center of the disk. The data is read from a CD-ROM by focusing a laser beam through the clear plastic on to the tracks.

CD-R (Compact Disk Recordable)
It is a write once medium. Here after writing data once it cannot be erased and write further.

CD-RW (Compact Disk – Read /Write)
The fact that CD-R disks cannot be erased and written has given rise to the development of CD-RW. CDRW allows a user to record over data or to delete individual files.

DVD (Digital Video Disk or Digital Versatile Disk)
Like CD, DVD has many different standards. These include DVD-ROM, DVD-Video, DVD-Audio, DVD-R, and DVD-RAM. DVD- ROM is high capacity data storage medium. DVD Video is a digital storage medium for movies. DVD-Audio is an audio-only storage format similar to CD. DVD-R is similar to CD-R and DVD RAM is a rewriteable form of DVD. With the same overall size as a standard CD, DVD disks can provide up to 17 Gigabytes of storage. The data transfer rate of a DVD is higher than a CD-ROM.


Processing Units
Central Processing unit (CPU) - The CPU is the brain of a computer and consists of three main parts: the control unit the arithmetic and logic unit (ALU) and the main memory. However, the processor usually refers to a combination of the control unit, ALU and associated registers.

The functions of the processor (CPU) are:
  • To control and coordinate the operations for the whole system.
  • To manage the main memory.
  • To fetch, decode and execute instructions.
  • The speed of processors is generally measured in MHz and GHz. For example, a 2 GHZ processor
  • Performs 2 X 109 pulses per second. The processor is connected via buses and lines to other part of the system.

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