HP Z800 Workstation
HP Z800 Resources:
HP Z800 Configurations (dv411.com)
HP Z800 QuickSpecs (US, HTML)
HP Z800 Support page (US, HTML)
HP Z800 Maintenance and Service Guide (PDF)
HP Z800 Memory Configuration: googling is the best bet as HP URLs change w/o notice (gotta love HP). Current URL as of July 2014: here (PDF)
PCIe slots
Slot 1 - PCIe 2 - x8(4) (mechanical/electrical)
Slot 2 - PCIe 2 - x16
Slot 3 - PCIe - x8(4)
Slot 4 - PCIe 2 - x16(8)
Slot 5 - PCIe 2 - x16
Slot 6 - PCI 32-bit 33MHz
Slot 7 - PCIe 2 - x16(8)