HP Z800 Revisions ???

Hi can someone help me understand what HP Z800 motherboard revisions there are.

I have brought a z800 with 1 x5690 and have purchased an additional x5690 , however i am tring to buy memory from ebay :

http://www.ebay.com.au/itm/48GB-64GB-96GB-8GB-605313-071-PC3-PC3L-10600R-DDR3-1333MHz-HP-DELL-IBM-APPLE-/142202433676?var=&hash=item211becf08c:m:mdxcvRK59Vni_XGxtbHqGWw

under description it says :

Z600 & Z800 Workstations with Rev C2 motherboard only ?? What is rev c2