Central processing unit
On modern computers, RAM is much slower than registers, so accessing RAM slows down programs. To speed up memory accesses, a faster type of memory called a cache is often put between the RAM and the main parts of the CPU. The cache is usually a part of the CPU chip itself, and is much more expensive per byte than RAM. The cache stores the same data as RAM, but is usually much smaller. Therefore, all the data used by the program might not fit in the cache. The cache tries to store data that is likely to be used a lot. Examples include recently used data and data close in memory to recently used data.