Difference between Windows Memory Diag & Memtest86?

[cpjust]

Hi,
I just got some bad RAM replaced and Memtest86 says the new RAM is fine (just as with the old bad RAM), but the Windows Memory Diagnostics goes up to 44% and just stops (it's not frozen, since I can change settings). With my old bad RAM (one stick was good and one was bad) Windows Memory Diag would get up to 100% on the good RAM but stop at 22% on the bad RAM.

Does anyone know what the Windows Memory Diagnostics is doing differently from Memtest86?
I always thought Memtest86 was supposed to be the best memory test program, but it's not detecting my bad RAM. I'm hoping OCZ didn't replace my old bad RAM with new bad RAM...

And I know the Windows Memory Diag program really was detecting bad RAM because my system would randomly lock up with the bad stick of RAM, but would run fine with the good one.

[User Name:]

So, does it still hang with the new RAM? If not, then try your BIOS's memory tester. You can let it be the final judge between Memtest and Mem Diag as to whethher the new RAM is faulty.

As to what they are doing differently... I don't know. The only way to test memory I know of is pretty simple, you just move patterns around all over memory and see if the are what they're supposed to be. I wonder if Memtest clears the cache. Does your processor have a rather large cache? Is your memory buffered?

[cpjust]

So, does it still hang with the new RAM? If not, then try your BIOS's memory tester. You can let it be the final judge between Memtest and Mem Diag as to whethher the new RAM is faulty.

As to what they are doing differently... I don't know. The only way to test memory I know of is pretty simple, you just move patterns around all over memory and see if the are what they're supposed to be. I wonder if Memtest clears the cache. Does your processor have a rather large cache? Is your memory buffered?

I've only had the new RAM a couple days, so I haven't had it long enough to know if it'll still lock up. I re-ran the Windows Memory Diag yesterday and this time I let it run longer than 3 hours and it actually got to 100% & passed (after 4 hours).

I don't think I've ever seen a BIOS that has a memory test built in.

I have an Intel Core 2 Quad (Q6600), and OCZ3P13334GK RAM (not sure if it's buffered...).

I guess I'll find out over the next few weeks if this RAM is bad or not. It's still really strange that Memtest86 would only take about 20 mins to finish the test and Windows Mem Diag takes 4 hours (but with my old good RAM it only took about 20 mins too).

[User Name:]

My POS $300(new) laptop has a built in RAM and HDD test.

This post(Memtest86+ Guide/How To's - Overclockers Forums) says that a correct running of memtest should take hours. Maybe you were only running one of the 10 he listed.

And, come to find out, memtest is cache aware. So, that is no the problem.

[cyberfish]

I'm fairly sure memtest disables cache.

BIOS memory tests tend to be primitive, and may not be able to catch all kinds of defects RAM can exhibit.

DRAM is basically a huge array of tiny capacitors, where charged = 1, uncharged = 0. Some capacitors can be leaky and refuse to charge, some chargers could be broken and would only charge or discharge the cap, sometimes changing one bit affects adjacent ones through leakage, etc. And then some leaky caps will have their charge lost over time, between refresh cycles.

Testing memory is not as easy as writing all one, reading back, writing all zero, reading back, and call it a day. A lot of failure modes cannot be detected that way.

To write a proper memory tester requires intimate understanding of how it works down to the electronics level, and all common failure modes.

The memtest author certainly sounds like he knows what he is doing.

I don't know what mem diag does, but I would probably trust memtest over it.

Unfortunately, memory errors tend to be intermittent, at least at early stages. I usually test my memory for 8 hours (leaving memtest looping overnight) when I get new computers, or suspect there's something wrong. I have seen errors that will only appear after a few hours, and errors that only appear when the module is heated up (heat increases capacitor leakage).