What is the difference between a cache, a primed cache and an empty cache?

Question

Can someone explain the following concepts to me as the relate to measuring the data transfer of data from my web site.

Whats the difference between a cache, a primed cache and an empty cache?

Can you give a a definition for each?

Solution

Cache: Some sort of memory-space for data to be stored, from here it is possible to retrieve data faster than the source location, in order to improve performance. For example, RAM on a computer can be used as cache for data on hard disk to improve performance. Another example is a web browser that has a local copy of something because it is faster than grabbing it over the net.

Primed Cache: A Cache that contains some of the data from the source location. So with the browser example, you may have a copy of an image saved on disk or in memory so you don't have to grab it over the net.

Empty Cache: Cache space that is available but has yet to have anything loaded into it. You have space to store some image from a web page, but never retrieved it so you don't have a cached copy yet.