Generally speaking, retrieving data from main memory is about four times faster than from a solid state drive, which in turn is about 150 times faster than from a server across the network. These values can vary a lot, but what’s certain is that the source of the data significantly affects the speed of retrieval.

Caching is the process of temporarily storing a copy of retrieved data in a more quickly accessible (lower latency) location, called a cache. It’s used to speed up applications by allowing subsequent requests for the same data to be served from the cache orders of magnitude faster than from the original source.