The architecture was based on the XserveG4.
The model with Firewire 800 is OS X only, but the 2003 non-Firewire can boot OS 9 and OS X.
Specs from Apple:
Processor – Single 1GHz, Dual 1.25GHz, or Dual 1.42GHz PowerPC
Ram – 256MB-2GB
Hard Drive – 60GB, 80GB or 120GB ATA/66-ATA/100
Graphics – GeForce4 MX or Radeon 9000 Pro
Optical – 12X DVD-ROM/CDRW or 2x DVD-R/CDRW
Wifi – optional airport (802.11b and Bluetooth)
Our Model M8570 has the Dual 1.25GHz processors, 2GB ram, dual 120GB Hard drives, Leopard 10.5.6, FW800, AVID DSP Farm cards. I adapted an ATX Power supply to run the system as the original PSU was DOA.