t7400 doubled ram and machine now runs slower

Hi jjulianrichards,

There are specific memory population rules for the T7400 and using only one riser will lead to a mismatch:

To achieve full bandwidth operation, memory configurations should consist of sets of four identically matched DIMMs to allow Quad-Channel operation. The sets of DIMMs must be identical with respect to capacity, rank, and organization (x4 or x8). Speed and CAS latency don't necessarily need to match, but the slowest speed DIMM and highest CAS latency will set the operating mode of the system.

For eight slot configurations:

• A single DIMM will work in DIMM1 or DIMM3 slot. This will be a reduced performance mode. BIOS will stop with an "F1/F2" message indicating this is a debug only mode. This mode is for use by tech-support to test a customer's DIMMs individually in the case of a reported memory failure.
• Configurations of two matched DIMMs are supported using DIMM1 and DIMM2 slots. This configuration provides half the memory bandwidth, but will be allowed to boot normally without any BIOS messages. This support is specifically to enable a low cost 1 GB (2 x 512MB) shipping configuration.
• Configurations of four matched DIMMs must use DIMM1, DIMM2, DIMM3, and DIMM4 slots. These configurations allow full bandwidth.
• Eight DIMM configurations use all eight DIMM slots and must consist of two matched sets of four DIMMs. These configurations have the same full bandwidth as four DIMM configurations.
• Additional non-shipping (but valid) configurations can be made by installing matched pairs of DIMMs in slots DIMM1/DIMM2, DIMM1/DIMM3, DIMM3/DIMM4, DIMM1/DIMM2 & DIMM5/DIMM6 and DIMM3/DIMM4 & DIMM7/DIMM8. These will result in dual channel operation which is lower bandwidth that quad-channel. We do not ship these configs, but they are valid and no error message is displayed.
• For thermal reasons, only DIMMs with a 'Full heat spreader' FLHS are supported. DIMMs with a heat sink only on the AMB will overheat and are not supported.

There's further information on page 179 here: 

http://downloads.dell.com/manuals/all-products/esuprt_desktop/esuprt_dell_precision_workstation/precision-t7400_user%27s%20guide_en-us.pdf

I hope this helps.

how can i tell if the machine is in test mode? the machine has been restarted some times now and run as it did prior to the ram addition. it just seems to react slower i guess, or almost as if the system board, processor and ram are outrunning the hard drive and i am noticing it just now for some reason.

If the system was in any kind of test mode you would see an on screen notification. 

well there is not any on screen indication so the problem lies elsewhere...yea. there are no other problems with the system that i notice in performance, only when i first pull something off the hd. i guess i will run pc check and see what that finds. thank you