If Gaz can't, I think I can....
These are from the Proliant series of rack servers. The board can have cache memory added via a SIMM slot and they are RAID compatible. They are SAS SCSI type units and they are PCI-X units, not PCI. They don't fit normal PCI slots.
I have one in a Proliant ML330 G3 system (that I got from Justin) and they are very quick.