Quote (Support PROGRAM topic in Registration)
They can have varying levels of intelligence, ranging from animal-level intellect to humanoid-intelligence. As far as appearance goes, they can be more or less anything you wish, but not too huge or too tiny; the support program frame starts getting errors when it tries to compile a frame that's too small, and a frame that's too large will become unstable.
...At least, that's the IC explanation. We just don't want people making ants or giant mecha support programs, really.