Memory Unit


The Central Processing Unit (CPU)


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 Memory Unit


The Memory Unit is the part of the computer that holds data and instructions for processing.
Although it is closely associated with the CPU, in actual fact it is seperate from it.
Memory associated with the CPU is also called primary storage, primary memory, main storage, internal storage and main memory.
When we load software from a floppy disk, hard disk or CD-ROM, it is stored in the Main Memory.

There are two types of computer memory inside the computer, RAM and ROM.



RAM stands for Random Access Memory.

This is really the main store and is the place where the programs and software we load gets stored. When the Central Processing Unit runs a program, it fetches the program instructions from the RAM and carries them out.

If the Central Processing Unit needs to store the results of calculations it can store them in RAM.

Random Access Memory can have instructions READ from it by the CPU and also it can have numbers or other computer data WRITTEN to it by the CPU.

The more RAM in your computer, the larger the programs you can run.

When we switch a computer off, whatever is stored in the RAM gets erased.

The following is a photo of a common RAM chip.



ROM stands for Read Only Memory.

The CPU can only fetch or read instructions from Read Only Memory (or ROM). ROM comes with instructions permanently stored inside and these instructions cannot be over-written by the computer's CPU.

ROM memory is used for storing special sets of instructions which the computer needs when it starts up.

When we switch the computer off, the contents of the ROM does not become erased but remains stored permanently. Therefore it is non-volatile.


The following is a diagram showing the relationship between the Central Processing Unit and the Main Memory (RAM and ROM).



Next PageHow the CPU worksPrevious PageArithmetic Logic Unit



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