Memtest86 5.01 failing to test RAM above 4 GB under certain circumstances

[UCyborg]

Very late to the party, should've done it way sooner, but finally got myself extra 2 GB of RAM so I'm at 6 GB now and immediately feeling less constrained. DDR2, ancient tech, difficult to get, especially if you don't fancy buying directly from strangers.

Computer turned on normally after installing it and off to Memtest86 5.01 I went, which was installed alongside Kubuntu 21.10. As soon as it started testing 4 GB - 6 GB range, endless error spam! Then I wasted time messing with BIOS settings such as timings and voltages, no improvement. The new-old stick is from another brand and has slightly worse timings, so the old sticks have to work a bit slower. Then I swap them around, put the original 2 identical sticks in the two slots most further away from the CPU and the new stick in the very 1st slot near the CPU, all related settings in BIOS to Auto, same problem, again only above 4 GB, where memory space of one of the old certainly working sticks reside now. What the hell, that makes no sense.

Then I take multiboot USB flash drive prepared with YUMI, which also has Memtest86 5.01 on it. With this one, it magically works, entire pass done with zero errors. Back to Memtest86 installed on the hard drive, errors in 4 - 6 GB range immediately. I repeat the tests again with original layout, so the old sticks in the first two slots and the new-old one in the 3rd slot with same results.

Now I'm really not sure anymore what computer issue I encountered in the past is the most bizarre. Just wanted to share this experience in case anyone encounters something similar. The RAM works fine. If there is a technical explanation, it would be nice to know it, but otherwise, if someone encounters this, a different installation of Memtest86 is worth a shot.

Maybe it has something to do with GRUB, which is how Memtest86 on the hard disk was launched while the one on USB flash drive was launched by SYSLINUX. But Kubuntu launched by the same GRUB certainly works without errors, I ran memtester (user-mode memory tester program) for a bit, got it to allocate 5 GB of RAM, which should definitely cover some portion of the extra stick.

Another person experienced the same issue with a bit more capable hardware, also AMD based, but AM3 CPU socket and DDR3 RAM and also using Memtest86 from Ubuntu, though he runs it from its install media, so either DVD or USB. One motherboard has AMD chipset, other has NVIDIA. Perhaps something to check if it still occurs with latest and greatest and check other distros that come with Memtest86. I wonder if it's a combination of multiple factors.

https://forums.tomshardware.com/threads/memtest86-errors-only-above-4gb.3751816/

Edited November 11, 2023 by UCyborg
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