Main memory is temporary memory. Data transfer between CPU and main memory is managed by the cache memory. Secondary memory is permanent memory. Data transfer between secondary memory and primary memory is managed by an I/O processor.

Scope

This article discusses the difference between main memory and secondary memory.

Definition

The differences between main memory and secondary memory are: 

Main memory	Secondary memory
Main memory is also known as primary memory or internal memory stores data temporarily	Secondary memory is also known as auxiliary memory or external memory stores data permanently
It can directly access data by processor/ CPU	It cannot directly access data  by processor/CPU
The nature of Parts of the main memory varies, RAM- is volatile in nature. ROM- Non-volatile.	Secondary memory is always non-volatile in nature
Memory is stored in semiconductor chips	Memory is stored in an external storage device such as hard disks, pen drives, etc
This memory has a fast access time	This memory has low access time.
It is expensive	It is inexpensive
Examples of main memory are: RAM and ROM	Examples of secondary memory are: magnetic disks, magnetic tapes, etc

SUMMARY

Main memory is also known as primary memory or internal memory has fast access time while secondary memory is also known as auxiliary memory or external memory has less access time. In primary memory unlike secondary memory data is directly accessed by the CPU

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