what is the actual cache memory & what's does?

Answer 1

Simple terms. cache is a "go between" memory, cpu, and/or harddrive. The larger it is, the more data it can help move around.
Best way to picture this is to say a bathtub is your ram memory (where programs run at, a lake is the harddrive (where data/programs are stored). The cache would be the bucket that moves the water (programs/data) from the hardrive to the memory in order to run.
It is also able to hold that data to wait until it's needed. Like when the cpu is trying to run calculations, the cache helps keep the data moving so the cpu doesn't have to wait for more data to be sent to it.

Answer 2

Cache memory is high speed memory that sits close to the processor. Basically, when the processor has to do work it must do it from within its registers (registers are also memory cells). In order to do this, it might have to load the values from memory into its registers. The first place it looks is cache memory, and if it finds it it copies it to registers to perform its operations. If it doesn't find it in L1 cache, it checks L2 cache, then it checks system memory, and the OS might have to page the memory from a page file. Note that each of these operations takes longer so its more preferable to have your data in L1 or L2 cache (and therefore better to have a larger cache).

Answer 3

In computer science, a cache is a collection of data duplicating original values stored elsewhere or computed earlier, where the original data is expensive (usually in terms of access time) to fetch or compute relative to reading the cache. Once the data is stored in the cache, future use can be made by accessing the cached copy rather than re-fetching or recomputing the original data, so that the average access time is lower.