What is Main Memory of the computer? OR Introduction to the Main Memory.



Main Memory

  • It is the working area of the computer.
  • All the running programs are stored in it.
  •  It consists of a chip in which millions of identical units are present.
  •  Each unit is called a cell or a bit.
  • A bit can store either 0 or 1.
  • Bits are organized in the form of bytes, which is the combination of 8 bits.
  •  Each byte has a unique address.
  •  Address of the cell is used to access the data.

This working area is of two types:
1) RAM                2) ROM

1) RAM:

  •  It stands for random access memory.
  • It is called random access memory because It’s any cell can be accessed directly in the equal time.
  • It is also called user’s memory because it stores all the programs, run by the users.
  • It is a volatile memory because it requires electric power to store and hold data.
  • RAM is a temporary memory because data is lost whenever electric power supply is switched off.

Following are the major types of RAM:
        a) SRAM              b) DRAM               c) MRAM

a)   SRAM:

  •  It stands for Static Random Access Memory.
  •  This type of RAM does not require electric refreshing.
  •  It requires less electric power.
  • It is expensive than DRAM.
  •  Its design is complex.


b)  DRAM:

  •  It stands for Dynamic Random Access Memory.
  •  It is slower than SRAM.
  • It consumes more electric power.
  • It is less expensive than SRAM.
  • Its design is simple.


c)   MRAM:

  • It stands for magneto resistant Random Access Memory.
  •   It is advanced form of RAM.
  •  In this RAM magnetic charges are used to store data instead of electric charges.


2) ROM:

  • It stands for Read Only memory.
  • It is also a working area but its contents are permanent.
  • It is also called system’s memory because it stores the routines of operating system.
  • Users can not change the data of ROM.
  • Manufacturer writes instructions in ROM at the time of manufacturing.
  • ROM is a non-volatile memory because it does not require electric power to hold the data.
  • ROM is permanent memory because data is not lost, whenever electric power supply is switched off.

Following are the types of ROM
i) PROM              ii) EPROM          ii) EEPROM

i) PROM:

  • It stands for Programmable Read Only Memory.
  • It is initially blank and manufacturer writes instructions in it at the time of manufacturing.
  • Writing is performed only for once and reading can be performed many times.
  • Data cannot be erased in it.


ii) EPROM:

  •  It stands for Erasable Programmable Read Only Memory.
  •   It is extended form of PROM.
  • Reading and writing can be performed many times.
  •  Data can also be erased with the help of Ultra Violet Rays.
  •  Portion of memory cannot be erased.


iii) EEPROM:

  • It stands for Electrically Erasable Programmable Read Only Memory.
  • It is extended form of EPROM.
  • Reading and writing can be performed multiple times.
  • Electrical signals are used to erase the data from EEPROM through some special devices.
  • Portion of memory can also be erased.



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