I have some RAM that is (apparently) bad. However, it passes a memory test just fine. Why?
I have an older-bordering-on-obsolete system that uses DDR2 RAM. Recently I came across 2x2GB DDR2 sticks, and since DDR2 is expensive/scarce these days, I wanted to give myself an upgrade (2x2GB to 4x2GB).
When I install the RAM, though, Windows (7) freaks out. Random crashes (app, kernel, and
driver!) everywhere within a few minutes. Last time I tried booting with the extra RAM in, Windows couldn't even get past boot and login without throwing a kernel panic.
So the obvious conclusion is that at least one of these RAM sticks is bad. I fire up the bootable version of Memtest86+
from a USB drive, and let the scan run for several hours.
But here's the part that I find perplexing: Aside from a single flurry of six errors (spaced very closely together) during one test, the memory tests good! I've been unable to reproduce the errors I encountered by rerunning the tests, either.
Yet, I boot into Windows again, and the errors start popping up again immediately. If I take the questionable RAM out, Windows behaves normally again with no errors.
So my question is: If this memory is so obviously error-prone that it makes Windows unusable within minutes, why the heck is it fooling the memory test? Is there a better memory tester I can try? And more practically, how do I find out which (both? one?) of the sticks is actually bad?
(Gory details that I don't think are relevant, but I'll include them anyways: My motherboard is a Biostar TA790GX, processor is Athlon 64 X2 6000+, and the RAM is Corsair DDR2 400 MHz. I'm hardware-literate enough to build/upgrade my own systems but I'm definitely not an advanced hardware geek.)