What are the differences between Primary and Secondary Memory?

The memory hierarchy is very crucial operation functionality in the computer and can be categorized into primary and secondary memory. Both these memories vary in the speed, cost and capacity. Primary memory is considered as a main memory that is accessed directly by the computer, so as to store and retrieve information. Secondary memory is considered as an external or additional memory, this memory is not directly accessed by the CPU because, the secondary memory is an external storage device, It can be used as a permanent memory, because even the computer is turned off we can retrieve the information.

 Primary Memory vs Secondary Memory

Primary memory vs Secondary memory
  • Processor access the primary memory in a random fashion. Unlike primary memory, secondary memory is not directly accessed through CPU. The accessing of the primary memory through CPU is done by making use of address and data buses, whereas input/ output channels are used to access the secondary memory.
  • The primary memory is embedded with two types of memory technologies; they are the RAM (Random Access Memory) and ROM (Read Only Memory). The secondary memory is accessible in the form of Mass storage devices such as hard disk, memory chips, Pen drive, floppy disk storage media, CD and DVD.
  • Primary memory is volatile in nature, while  secondary memory is non volatile. The information that is stored in the primary memory cannot be retained when the power is turned off. In case of secondary memory, the information can be retrieved even if the power is turned off because the data will not be destructed until and unless the user erases it.
  • When the data processing speed is compared between the primary and secondary memory, the primary memory is much faster than the secondary memory.
  • In the cost perspective, the primary memory is costlier than the secondary memory devices. Because of this reasons most of the computer users install smaller primary memory and larger secondary memory.
  • As the secondary memory is permanent, all the files and programs are stored in the secondary memory most and as the primary memory interacts very fast with the micro processor, when the computer needs to access the files that are stored in the secondary memory, then such files are first loaded into the primary memory and then accessed by the computer.


The following table list out some of the key differences between the primary and secondary memory:

Primary memory Secondary memory

The memory devices used for primary memory are semiconductor memories

The secondary memory devices are magnetic and optical memories.

The primary memory is categorized as volatile and non volatile memories, RAM is the volatile memory and ROM is the non volatile memory

The secondary memory is always non volatile

The primary memory is composed of programs and data that are presently being used by the  micro processor

The secondary memory is enough capable to store huge amount of information

The primary memories are more effective and fast to interact with the micro processor

The secondary memories are somewhat slow in interacting with the micro processor, when compared with the primary memory.

Primary memory is known as main memory

Secondary memory is known as additional memory or back memory

These memories are also called as internal memory

These memories are also called as external memory

Primary memory is temporary

The secondary memory is permanent

Commonly used primary memory (main memory) available in the range of 512 MB to 8 GB RAMs.

Generally secondary memories range between 80 GB to 4 TB Hard Disc Drives.

The primary memory devices are connected to the computer through “slots”

The secondary memory devices are connected to the computer through Cables

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