Primary Memory and Secondary Memory in Computer

The computer memory can be categorized into two: the primary memory and secondary memory. You know that memories in computer are used to store data, programs, and the results.

Primary Memory and Secondary Memory

The two types of computer memories are primary memory (Volatile Memory) and secondary memory (Non Volatile Memory).

Primary Memory

The primary memory is also called the volatile memory which means they on’t have the permanent storage capacity. The data stored in the primaries will be erased ones it lost the electric power.

  • The primary memory is also called as the main memory of the computer. They are directly accessible by the CPU of the computer.
  • The currently executed data and instructions are copied into the primary memory.
  • These type of memories are made up of semiconductors.
  • The data reading and writing is much faster in primary memories.
  • Primary memory of a computer will be small in size.
  • Primary memories are accessed by data bus.
  • Primary memories are internal memories and is costlier than secondary memories.

The two types of primary memories are:

  • Random Access Memory (RAM)
  • Read Only Memory (ROM)

Random Access Memory

The Random Access Memory is one type of primary memory which has the both capabilities of read and write. The RAM stores the data that has to be currently processed by the CPU. The data stored in the RAM will be lost at the power failure.

There are two types of random access memory. They are:

  • Static RAM (SRAM)
  • Dynamic RAM (DRAM)
Static Random Access Memory
  • Retain stored information as long as power is on.
  • Cost less and consumes more power.
  • Higher speed.
  • Hold information in a flip-flop consisting of 2 cross coupled inverts.
  • Requires 6 transistors.
Dynamic Random Access Memory
  • Losses it’s stored information in a very short time even though the power supply is on.
  • Binary state is stored on the gate source stray.
  • Charges on capacitors lack away as a result of normal leakage in a few milliseconds out needs to refresh periodically in every two milliseconds.
  • Moderate speed.
  • Cheaper at cost.
  • Consumes large capacity of memory used in main memory.
  • Only one transistor is needed because information is stored in stray capacitor.

Read Only Memory

The ROM is a read only memory. In ROMs the content cannot to be altered. ROM is a non-volatile memory in which the data will not be erased at the power off.

The various types of read only memories are:

  • Masked ROM
  • PROM
Masked ROM

The programs or data are permanently stored at the time of manufacturing. The data in the Masked ROMs cannot be altered.


The PROM or Programmable Read Only Memory has the same functions of Masked ROM expect, the user can program the ROM for the first time.


In Erasable Programmable Read Only Memory or EPROM, the data can be erased by exposing ultra-violate light.


The Electrically Erasable Read Only Memories are those memories which has the same features of EPROM. But the data can be erased by using electrical signals instead of ultra-violet light.

Secondary Memories

The additional memories used in the computer are called Secondary Memories. These memories are non-volatile because the data storing is permanent.

  • The secondary memories are not directly accessible by the CPU.
  • Secondary Memory is the auxiliary memory of the computer.
  • The Data to be stored in computer is kept in the secondary memories.
  • Secondary memory is non-volatile memory.
  • These type of memories are made of magnetic and optical materials.
  • Accessing data from secondary memories are slower than primary memories.
  • The secondary memory is accessed by the input and output units.
  • The secondary memories of a computer will be much larger than primary memories.
  • Secondary memories are cheaper than primary memories.
  • Secondary memories are the external memory of a computer.

The examples of secondary memory are Hard disk, CD, DVD, etc.

If you have any doubts on primary memory and secondary memory feel free to comment below.

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