Only the 6GB (6 x 1GB) and 12GB (6 x 2GB) configurations are supported. Memory configurations which mix and match memory module sizes and locations will result in a poor performing, non-optimal operating environment. 2.) Qualified Operating System for Avid Client Editing Applications and Hardware on the HP Z800: - Supported: Microsoft® Windows Vista Business 64-bit Edition (SP1 / SP2) - Supported: Microsoft® Windows Vista Ultimate 64-bit Edition (SP1 / SP2) - Not Supported - Microsoft® Windows X