title: What is git-cache and what is stored in the git-cache
body: <p>Actually, I read a lot of things about git.</p>
  <p>I know I can remove cache by <code>git rm --cached .</code> command but I can not understand the concept of <em>git-cache</em>.</p>
  <p>What is cache? And where is the location of caching in GIT? Is this cache stored in RAM or in a file? Is cache used to improve performance in git?</p>
  <p>What is stored in the cache?</p>