On Tue, 27 Jan 2015 15:28:11 -0800 walt wrote: > 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.
As an addition to earlier posted comments: 1) memtest86+ has a bit fade test which is not enabled by default (at least for 4.x branch which is the latest in tree now), so you have to enable and run it manually. IIRC it is enabled by default in 5.x branch (bug pending in bugzilla). By the way 5.x have some additional tests which may find faults unknown to 4.x 2) The same frequency is not enough to guarantee memory banks compatibility. They may require different timings or, less probably, voltage. Some BIOS tuning may help here. 3) Memory may be (un)buffered, (un)registered, ecc/non-ecc. Many of these combinations are not compatible with each other. 4) In some rare cases even banks with the same parameters from different manufacturers are not compatible due to technological differences (this goes down to how logical circuits are implemented). Best regards, Andrew Savchenko
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