Possible Duplicate:
free memory in Linux
I'm trying to determine if my server needs more memory.
free -m
total used free shared buffers cached
Mem: 7993 7719 274 0 372 5866
-/+ buffers/cache: 1480 6513
Swap: 11617 0 11616
The cached is high and free is low (the server handles a lot of requests). Is this indicative that the server could benefit from additional memory since all free memory is being used as cache?
No, that's what Linux does: it takes up the bulk of free RAM and uses it as cache. If processes require more memory, cache will be released for those processes.
The relevant line is the "-/+ buffers/cache" one, which indicates that you have 6.5 essentially free. Also of note, you're not using any swap, so you've haven't hit a high memory usage situation.
This article gives a lot of useful information how to interpret free output.