2011/2/17 Kris B <b.kris24@...>

>
> total used free shared buffers cached
> Mem: 4046784 905792 3140992 0 195728 428392
> -/+ buffers/cache: 281672 3765112
> Swap: 2096376 0 2096376
>
> This is the result of free - at that time there were 6 users connected to 3 DBs.
>

so you should not have problem if you let 75 as page Buffers when you
use Classic or SuperClassic

if you want to use more ram, use tmpfs
Firebird can use it for temporary files need for sort, etc ...
and let ram so your filesystem manage its own cache

http://wiki.centos.org/TipsAndTricks/TmpOnTmpfs