The CPU cache is a temporary holding place for recently accessed information. It stores copies of the data from the most recent memory accesses so that quick, repeated accesses would not have to travel all the way to the main memory. This speeds up processor operation by keeping it fed with data, though slowdown is possible if there are too many concurrent requests for information in the main memory.
Data are swapped between cache and memory as needed. Cache layers contain more powerful but slower-clocking versions of microchips found in RAM modules, making their contents available faster than those of main system RAM, but at the expense of somewhat less storage capacity per unit weight or size.