The computer memory is one of the most important elements in a
computer system. It stores data and instruction required during the processing of data and output results. Storage may be required for a limited period of time, instantly or for an extended period of time. It also relates to many device that are responsible for storing data on a temporary or permanent basis.
Memory Hierarchy
The hierarchical arrangement of storage in current computer architectures is called the memory hierarchy. The computer uses a hierarchy of memory that is organised in a manner to enable the fastest speed and largest capacity of memory as shown in figur. The memory is characterised on the basis of two key factors; Capacity and Access Time.
Parameters Of Memory
1. Storage of Capacity
2. Access Modes
3. Access Time
4. Physical Characteristics
5. Permanence of Storage
Types of Memory
Primary Memory
The memory unit that communicates directly with the CPU is called main memory or internal memory or primary memory. The Primary memory can be further classified in two categories:
1) Random Access Memory ( RAM )
It also known as read/write memory, that allows CPU to read as well as write data and instructions into it.
There are two categories of RAM
1: Dynamic RAM
2: Static RAM
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2) Read only Memory ( ROM )
It also known as non volatile memory or permanent storage. It does not lose its contents when the power is switched OFF.
There are three categories of ROM
1: Programmable ROM
2: Erasable Programmable ROM
3: Electrically Erasable Programmable ROM
Secondary Memory/Storage
This memory stores much larger amounts of data and information for extended periods of time. Data in secondary memory cannot be processed directly by the CPU, it must first be copied into primary memory. i.e RAM. It is slower and cheaper form of memory.
Secondary Storage is used to store data and programs when they are not being processed.
It is also NON-Volatile in nature.
Secondary memory devices include as follows:
- Magnetic Storage
- Optical Storage
- Solid State Storage
