Fundamentals of Computer > Computer Memory > Classification of Memory

Classification of Memory

Memory can be classified according to a number of criteria:

• Storage capacity
• The method of storing and retrieving data
• The time needed to store and retrieve data
• Connection of memory device with the CPU
• Storing data temporarily or permanently
• Cost per bit of storage etc.

Primary Memory (Main Memory)

Primary memory is directly connected to the CPU. Every location in main memory can be directly and randomly accessed by the CPU. However, the primary memory can hold information only while the computer system in on. As soon as the computer system is switched off or reset, information stored in the primary memory disappears. Hence, primary memory is sometimes referred to as the volatile or temporary memory. Moreover, primary memory normally has limited storage capacity, because it is very expensive. The primary memory of modern computer system is made up of semiconductor devices.

This memory-

• holds data and instructions before the actual processing starts
• intermediate results of ongoing processing
• final results of processing before being passed on to the output units.

Example of primary memory: RAM, ROM. 

 

Secondary Memory (Auxiliary Memory)

Secondary memory is used for storing programs and large data files which are currently not required by the CPU, but at later time they may be needed for processing. This memory can retain information even when the computer system is switched off or reset, i.e. it holds data permanently. It is much larger in capacity but much slower than main memory. It also serves as an overfollow memory when the capacity of the main memory is exceeded. Secondary memories that have huge capacity  are termed as bulk memory or storage.

Example of secondary memory: hard disk, compact disk (CD), digital versatile disk (DVD), Pendrive, etc.

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Differentiate between Primary and Secondary Memory

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