Re: [gentoo-user] Question about flakey RAM

[Mick]

On Thursday 29 Jan 2015 22:13:28 Volker Armin Hemmann wrote:
> Am 28.01.2015 um 00:28 schrieb walt:
> > Yesterday I installed 4GB more of RAM in this machine for a total of 8GB,
> > and the machine soon began random segfaulting and even a kernel crash or
> > two, so obviously I suspected the new RAM was faulty.
> >
> > I let memtest86+ run overnight and it found zero memory errors. Today I
> > exchanged the new RAM anyway and got a different brand this time, and
> > that fixed the problem.
> >
> > My question is why didn't memtest86+ find any errors?  Could it be that
> > the first RAM I bought was actually okay but this machine didn't like it
> > for some reason?  Both were DDR3/1333MHz, just from different
> > manufacturers.
>
> Since this was not mentioned yet:
>
> Maybe because the ram was not faulty at all.
>
> Maybe it really operated in the range of allowed tolerances - and those
> were never crossed with memtest as a very light system load.
>
> But with an OS booted, the CPU, graphics solution, harddisks all sucking
> power like mad, your mainboard or PSU might not be able to deliver as
> stable currents as the specifications demand. Some memory is more
> tolerant than other.

Yes, I've witnessed this too after adding 2 new memory modules of a different 
size to the originals and from a different manufacturer, in a box with a 
suspect PSU.  Memtest+86 was not erroring out, but the system was crashing 
when put under pressure.  Typically I would get errors when more than the size 
of the old memory started being used.  This got worse over time, as the PSU 
components were ageing.  Eventually I replaced a capacitor in the PSU and the 
memory problems disappeared.

It has been already mentioned, but it is worth noting that some BIOS/MoBos are 
more sensitive to different brands of memory.  In those cases I found that 
using the same make and size modules resolves the problems.
-- 
Regards,
Mick