Primary Memory

Primary Memory

        The primary memory of the computer is used to hold two distinct types of information, the data which is to be processed by the CPU and the set of of instruction to be executed next.The primary memory is capable of sending and receiving data at very high speed.The primary memory is classified into two

=>Random Access Memory (RAM)

=>Read Only Memory (ROM)

RAM : 

   

   RAM is used to to store data and instruction needed by the CPU for processing.Data can be stored and retrieved at random from anywhere with the same amount of time, no matter where the data is.Hence the name random access memory .RAM can be used for both reading(retrieving) and writing(storage) of data.So it is also called Read/Write memory.

   Data can be stored in RAM only temporarily because memory is electronic device and hence is of volatile nature.When electronic power is turned off all the contents of the RAM will be lost.CPU requires all the data and instruction under processing to be in the main memory (RAM).So data and instruction should be reloaded  to the main memory every time when the computer is turned on.

   RAM was one of the most expensive computer component to manufacture for many years.Vacuum tubes, transistors and magnetic cores were used in earlier times as memory.However with the invention of semiconductor technology the cost of manufacture and size of memory has drastically reduced.Today the usage of silicon chips has greatly increased the memory capacity of computers.Based on the characteristics of the electronic circuits, RAM exist in various forms like Static RAM, Dynamic RAM (DRAM), Synchronous Dynamic RAM (SDRAM).

ROM :

   Read only memory is a memory unit that can perform only read operations. it does not support storage or write operations.Binary informations stored in ROM are permanent nature and they are stored in the ROM chip at the time of manufacture itself.Hence ROM is of non volatile nature i.e., contents are not lost even if power is turned off.However components connected to the systems perform some basic input/output operations, initiates loading of software that are essential for the working of the computer system.ROM chip is also called Firmware because these instruction are permanently stored in it at the time of manufacturing.

     

     There are exists another three categories of ROM used in some computer system namely

=> PROM (Programmable ROM)

=> EPROM (Erasable Programmable ROM)

=> EEPROM (Electrically Erasable Programmable ROM)