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Primary and Secondary Memory.

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Primary Memory

  • Primary memory is the main memory of computer. It is used to store data and instructions during the processing of data. Primary memory is semiconductor memory.
  • Primary memory is of two kinds Random Access Memory (RAM) and Read Only Memory (ROM).
  • RAM is volatile. It stores data when the computer is on. The information stored in RAM gets erased when the computer is turned off. RAM provides temporary storage of data and instructions.
  • ROM is non-volatile memory, but it is a read only memory. The storage in ROM is permanent in nature and is used storing standard processing programs that permanently reside in the computer. ROM comes programmed by the manufacturer.
  • RAM stores data and instructions during the execution of instructions. The data and instructions that require processing are brought into the RAM from the storage devices like hard disk. CPU accesses the data and the instructions from RAM, as it can access it at a fast speed than the storage devices connected to the input and output.
  • The input data that is entered using the input unit is stored in RAM, to be made available during the processing of data. Similarly, the output data generated after processing is stored in RAM before being sent to the output devices. Any intermediate results generated during the processing of program are stored in RAM.
  • RAM provides a limited storage capacity.

Secondary  Memory 

  • The secondary memory stores data and instructions permanently. The information can be stored in secondary memory for a long time, and is generally permanent in nature unless erased by the user. It is a non volatile memory.
  • It provides back-up storage for data and instructions. Hard disk drive, floppy drive and optical disk drives are some examples of storage devices.
  • The data and instructions that are currently not being used by CPU, but may be required later for processing are stored in secondary memory.
  • Secondary memory has a high storage capacity than the primary memory.
  • Secondary memory is also cheaper than the primary memory.
  • It takes longer time to access the data and instructions stored in secondary memory than in primary memory.
  • Magnetic tape drives, disk drives and optical disk drives are different types of storage devise.


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