Friday, October 10, 2008

Computer Memory (RAM, ROM, PROM, EPROM, floppy disk, CD ROM, CD writer, DVD, Hard disk, pen drive)

The computer stores the data in an area known as memory. It can be compared to thousands of registers and files maintained in an office. The computer stores data in the forms of binary digits (0s and 1s) or Bits. The units are

  • 8 Bits :1Byte
    1024 Bytes :1Kilo Byte (KB)
    1024 KB :1 Mega Byte (MB)
    1024 MB :1 Giga Byte (GB)
    1024 GB :1 Tera Byte (TB)

Memory can be classified into two types, namely

  • Primary Memory
  • Secondary Memory

Primary Memory or Main Memory is used to hold the program being executed and any other data currently in use. It is of two types namely:

Random Access Memory (RAM). Random access memory is Volatile Memory. It is also called Read/Write Memory. When the computer is switched off, information stored on the RAM is lost. Hence it is also known as Volatile Memory.

Read Only Memory (ROM). There are certain functions that the computer must perform when it is switched on. For example, connections have to be established within the various components if the computer and its peripherals. A series of programs are required to perform these functions. These programs are hardwired into the ROM Chips at the time of manufacture. ROM is non-volatile. When the computer is switched off, the data on these chips is not lost. Hence it is known as Non Volatile memory.

Programmable Read Only Memory (PROM). A variation of the ROM chip is PROM. PROM can be programmed to record information using a facility known as PROM Programmer. If the chip is programmed, the recorded information cannot be changed and PROM becomes ROM. This is also Non-volatile.

Erasable Programmable Read Only Memory (EPROM). Information in these chips can be erased by exposing them to ultra-violet rays. The chip can then be programmed afresh to record different information.


Secondary Memory or Auxiliary Memory is the area in which the processed data or information can be stored. The devices used are known as secondary storage devices.

Floppy Disk. It is a flexible plastic disk coated with a thin layer of Iron Oxide. They are available in three sizes viz. 31/2, 51/4 and 8 inches. The commonly used is the 31/2” floppy disk. The storage capacity of these disks is limited (1.44 MB).

CD ROM. CD ROM (Compact disk- Read Only Memory) has larger storage capacity. However to transfer information from your computer to the CD, you require a device known as a CD Writer. The CD can hold data amounting to 700 MB. A more advanced version is the DVD which can hold data anywhere between 1 GB and 16 GB.

Hard Disk. The Hard Disk is another storage device, which is fitted to the computer so that the processed data can be stored and accessed easily. The software required to run the computer and any additional software or programs are stored in the hard disk. The new version computers are equipped with 40, 80 or 160 Giga Bytes Hard disk.

Pen Drive. It is a small, dust proof, shock proof, very light weight storage device, used to transfer files between USB compatible systems conveniently. It is available in a range of capacities even up to 8 GB or more.