Hi. For a personal project (for the learning experience) I am planning to a make a Gentoo-based computing cluster out of old PCs, following the basic instructions here:

http://www.gentoo.org/doc/en/hpc-howto.xml

As I start into this, though, there is one concern that bothers me, and I don't want to get the answer through trial and error, for obvious reasons: Do the PCs systems have to have the same processor speed and RAM for this to work? All the equipment I have is of various makes and models.

It would make setup and maintenance easier if they were all the same, but they don't have to be identical for the cluster to function.

Keep in mind though that there is considerable overhead when running a cluster, and with outdated hardware it is unlikely that even a dozen nodes could outperform a single modern machine. Since you are doing this just to learn it doesn't sound like that will be a big deal for you, but just don't expect to be blown away.

This makes sense to me... but I suppose there might be technical details of which I am not yet aware.

Ha! Won't you be surprised when I take over the world with my raw computing power! Wha ha HA HA HA! Now, if I can just find another 30 million Pentium IIIs laying around...

Actually I'm wondering, with all the old Ethernet cards I have, if inter-process communication will even be fast enough to make working in the cluster faster than working on just one of the nodes. But that is something I don't mind finding out through trial-and-error.