The performance of a microcomputer system can be significantly improved by introducing a small expensive but fast memory between the microprocessor and main memory. This memory is called cache memory and this idea was first introduced in the IBM 360/85 computer. Later on this concept was also implemented in minicomputers such as PDP-11/70 with the advent of VLSI technology, the cache memory technique is gaining acceptance in the microprocessor world.
The relationship between the cache and main memory blocks is established using mapping techniques. Three widely used mapping techniques are
- Direct mapping
- Fully associative mapping
- Set associative mapping
In the direct mapping the main memory address is divided into two fields an index field and a tag field. The number of bits in the index field is equal to the number of address bits required to access the cache memory. There are two ways of writing into cache the write back and write through methods, in the write back method whenever the microprocessor writes some things into a cache word a thirty bit is assigned to the cache word.
