Primary Memory or Main Memory

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Primary Memory or Main Memory

The main memory is used to store data and instructions currently required for processing. These memories are manufactured by using integrated electronic circuits or semiconductor device. It has limited capacity and data is lost when power is switched off. Both RAM and ROM are random access memories and both can be used for reading purposes. The distinguishing feature is RAM's ability to alter data stored in it, which is not possible with ROM. Typically ROM is used to store system instructions which are relatively permanent in nature. RAM is volatile; that is, it loses its contents if the device is electrically disconnected.

Primary Memory are divided into two subcategories :
1. Random Access Memory (RAM)
2. Read Only Memory (ROM)

Random Access Memory (RAM)

The word 'random' means that the computer can access any memory cell without accessing all cells sequentially. That is, a memory is said to be random access memory if any part of it can be accessed directly (randomly) for reading or writing data in the same time irrespective of its location. In other words, access to this memory is independent of physical storage location of information on the medium. RAM is volatile as any interruption in power supply results in loss of data in RAM. The contents of the memory remain there as long as electrical current is available to sustain the memory's pattern of positive and negative charges which represent the two bits 1 and O.lf power fails, all the contents in the memory will be lost.
Types of RAM :
• Dynamic Random Access Memory (DRAM)
• Synchronous Dynamic Random Access Memory (SDRAM)
• Static RAM
• Video RAM
• Flash RAM

Read Only Memory (ROM)

This memory uses MetaL Oxide Semiconductor TechnoLogy. RAM is read-write memory whereas ROM is Read-OnLy-Memory. This memory is used to store frequently used programs in the system.
Types of ROM :
• Programmable read-only memory (PROM)
• Erasable programmable read-only memory (EPROM)
• Electrically erasable programmable read-only-memory (EEPROM)


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