The storage locations of a computer are often though of in a heirarchy. At the top are the fastest but smallest locations, the registers of the CPU. At the bottom are the slowest but largest locations, hard drives and other forms of high-capacity long-term storage.
In between the registers and system RAM, we have the processor’s cache. The cache is controlled automatically by the CPU such that, when it reads bytes from memory, those bytes get stored in cache. As long as those bytes of memory remain copied in cache, the CPU can subsequently read the cache instead of having to go out to actual memory.
Today’s newer CPU’s have caches of a few megabytes in size. Computationally intensive programs tend to run significantly faster when they can use the cache to avoid going out to actual memory as much as possible.
