What Is The Cache Memory And How It Works?

It is a small memory which contains a copy of a portion of main memory. It is useful because it gives the data very fast and don't copy the whole RAM data. Cache works on guess.
Its working is very simple and efficient, like CPU read a word from cache, if it is not found, cache imports BLLOCK of required data from main memory, means processor want to read a page 34 or ch-3 and the ch-3 contains 1-90 pages, so when processor ask for the page 3 from cache, it cache have this page then it will give this page to the processor, if it don't have this page then it will ask for this page to the RAM, then cache will take the full ch-3 (full block) and will send the page to the processor, it keep the full ch-3 with itself because it thought that,  most probably the processor will read the next page from this chapter. So it is the whole working of the cache memory. As I said cache work on guess, that's why it keep the whole chapter with itself. Via this the CPU work very efficiently. Initially this cache was came only for the main memory, but now it is used for many hardware devices like cd-drive and many other, it is very helpful for the fast data processing.