I have a Dell Precision workstation 490 and increased the initial one GB ram (two 512MB sticks) to five by adding two 2GB sticks after I upgraded the op system to Windows 7 Pro 64bit and I have installed the most recent BIOS. There was no problem, the system recognized five GB of memory.
I have bought two 4GB sticks and added them. The system in Setup now only recogizes nine GBs. I took all the memory out and reinserted the two 4GB sticks to check. The system reported no memory fitted! I took them out and reinserted the two 2GB sticks together with the two 4GB sticks. The system now lists four 2GB sticks of memory when it should be twelve the total installed memory is 4GB though.
Is there something wrong with the 4GB memory sticks? They were bought secondhand. All the memory is ECC FBD
The Dell has eight memory slots. The slots are marked as different by having four slot retainer clips cream and four black. I could understand that each "bank" might need four similar sized memory sticks, but then the Dell manual doesn't mention that.
I ran memory diagnostics and all the memory is OK. System Information reports 8GB installed memory but total physical memory 4GB. Available physical memory 3.05GB Available virtual memory 7.99GB and Available virtual memory 6.96GB
From Control Panel > system View Basic Info: Installed memory is reported as "8.00 GB (4.00 GB usable)"