HP BL685C G6 - Manual (Page 12)

Component identification 12
• Processor 3 DIMM slots
• Processor 4 DIMM slots
For installation guidelines and population order, see "Memory option (on page 37 )."
Mezzanine connector definitions
PCIe x8 mezzanine connectors support x16 cards at up to x8 speeds.
Item Connector Card support
Mezzanine connector 1 PCIe x8 Type I mezzanine card only
Mezzanine connector 2 PCIe x8 Type I or II mezzanine card
Mezzanine connector 3 PCIe x8 Type I or II mezzanine card