Question : Problem: RAM OK in 32-bit OS, but fails with Vista 64-bit. Why?

I've been happily running Vista Business 64-bit on my desktop for months.

Then the 64-bit installation started blue-screening, although if I re-install 32-bit Vista or 32-bit XP from images or if I install 32-bit Linux onto the same system there's no problem

The same problem occurred when I tried to do a Vista 64-bit clean install. Using 2 different Windows DVDs.

The RAM passed memtest86+ but nevertheless when I removed 2 x 1GB sticks the problem disappeared.

Can anyone tell me why 64-bit Vista seems to be sensitive to the apparent RAM problems but not 32-bit?

Is it possible that the defect is in the part of RAM not addressable by 32-bit OSs? With my configuration that is about 500MB.

I think I've eliminated the possibility of a RAM slot defect. 2 x 1GB modules work OK in either pair of slots.

Asus M2N32-SLI Deluxe motherboard
Athlon 6000 CPU
NVIDIA 8600GLS
4 x 1GB 533MHz RAM
Vista Business 64-bit

Answer : Problem: RAM OK in 32-bit OS, but fails with Vista 64-bit. Why?

I'm not surprised you get solid results with 2 modules but have issues with 4.   All motherboards that use unbuffered modules will run more reliably with only 2 modules installed due to much lower electrical loading on the address and data buses.   As to why it works in 32-bit OS's and not 64 => the 64-bit OS is more aggressive in its memory utilization, and is thus more sensitive to the loading issues.

The BEST solution is to install 2 x 2GB modules instead of 4 x 1GB.   But you MAY be able to improve things by either or both of these changes:  (a)  Slow down the memory access ... add 1 cycle to each of the strobe timings [i.e. if you have 5-5-5-18 memory change it to 6-6-6-18]; or (b)  increase the memory voltage by 0.1 or 0.2 volts.