Is memtest always right?

[wyliecoyote]

Hi all

I have a windows 7 pc that freezes every time on the starting windows screen.

Even trying to start safe mode it will freeze, and the same if I try start up repair with or without disks.

So basically I can't get in to do anything.

I have tested all components within the pc. Tried a different psu, checked hdd for errors, unplugged devices not needed etc.

I ran memtest86 on the ram and even that came up fine, so I was at a bit of a loss.

However I remembered a stick of ddr3 ram that I had lying around and thought " what the hell I'll try it". So I took out the ram already in there and replaced it with that stick. The pc now boots fine every time.

So could it be something else or is memtest wrong sometimes?

Thank you in advance

[David (PassMark)]

Some RAM errors can be missed because of factors like,

A) Not all the RAM is tested by MemTest86, or any another tool for that matter. This is because BIOS reserves some address ranges for other functions (memory mapped I/O). So there will be between 1 - 5% of RAM not tested on most systems.

B) MemTest86 tests the RAM more or less in isolation. So the video card and disk aren't under load while the RAM test is running. Depending on your BIOS and CPU type, then maybe even the CPU isn't very loaded. Some errors might only manifest themselves under high system load. For example high video card load might dump extra heat and EMI into the system causing RAM errors that you don't see otherwise. Or maybe the PSU isn't up to the job when under high system load, but is OK when just running a RAM test. Our BurnInTest product can help with testing in this case.

C) The older releases of MemTest86 were 32bit only. Where are nowadays most systems are using 64bit and use SIMD as well. So it is possible some flaws only come to light when 64bit instructions are executed. V4 of MemTest86 was 32bit. Whereas V5 and V6 of MemTest86 are native 64bit. (Note that there is another older version of MemTest, called MemTest86+, which is also 32bit only).

D) There are classes of RAM errors that aren't tested in older MemTest86 releases. 'Row hammer' being the main one. We are adding a new test in V6 to cover this.