What is the difference between a Google Index and a Cache?

I know that Google produce results by keeping indexes of webpages, but how do these differ from their cache (which is an older version of the page). Does Google have an Index AND a cache?

A cache is not google, a google index is google.

Google takes a snapshot of each page examined as it crawls the web and caches these as a back-up in case the original page is unavailable. If you click on the "Cached" link, you will see the web page as it looked when we indexed it.

while, Google creates the index and the database of documents that it accesses when processing a query.

the cache is sort of a dumping folder for files that are in use but not required for normal operation. it's a folder that is used with most programs to put uncompressed files in so, and the files within can usually be deleted without conciquence, as the program will reload them if it needs them.