How does the fedora brewbuilder work?

[Mark]

> Brew is the internal Red Hat build system.  Koji is the new, open
> build system used for Fedora>= 7.

Sorry, i meant Koji.
I did found some info on the wiki about koji and xen but i'm actually
surprised that the build system is so simple.. i expected a heavy
cluster of about 10 or more quad core cpu's that are all dedicated to
compiling programs but it doesn't seem to be the case. But than the
question still stands.. what kind of powerhouse is that koji
(xenbuilder) machine?