There are various ramfs systems you can use (eg, ramfs, tmpfs), but in general if files are actually being read that often, they sit in your filesystem cache. If your working set of files is larger than your free ram, then files will be cleared out of it - but if your working set is larger than your free ram, there's no way you'll fit it all into a ramdisk either.
Check the output of the "free" command in a shell - the value in the last column, under "Cached", is how much of your free ram is being used for filesystem cache.