Poor Performance With 4GB Memory

I recently added 2GB of memory to my P4P800 for a total of 4GB, and immediately began experiencing visible performance problems most noticeably in games. After much troubleshooting, I discovered that setting Maximum Memory in System Configuration (msconfig.exe) to 3300MB (I didn't test every 1MB below the limit, by the way), down from the limit of 3328 (using 1 or 2MB less than this still resulted in performance problems...) restored performance to pre-4GB levels. I'm aware of x86 architecture not being able to utilize 4GB of memory, so this isn't about that. Additional oddities include PCI Latency Timer (of all things...) effecting performance and lower memory timings being more stable than high... What's going on here? Is there any way to avoid adding a memory limit?

Windows Vista with SP1 (32-bit)
Asus P4P800 with BIOS 1021.006
Pentium 4 3.0E at 3.75 (250FSB)
Corsair PC3200 4GB (4x1)
GeForce 7800 GS at 520/725
Audigy 2

You could possibly be running into problems with all four dimm slots filled with memory. In fact Corsair usually recommends downclocking your memory when filling all four dimm slots. See here: Full dimm slots - Please school me. - The Corsair Support Forums. Follow the links posted by DereKT.

Also be aware that the more memory your v-card(s) have, the less system memory you have for non video system resources under a 32bit system since 32bit OS' are limited to 4gig of memory. See here: http://www.corsair.com/_appnotes/AN804_Gaming_Performance_Analysis.pdf.

Other then that, make sure you have "manually" set the recommended memory timings and voltage as stated by the RAM manufacturer.

Good luck

try to use 64-bit version of vista

i am using it now and have now problems at it