How do I interpret these Rember errors?

[theorist9]

I have a 2019 27" i9 iMac running Ventura 12.6. I bought four used 32 GB Apple OEM RAM sticks from OWC. One stick in a pair was bad (iMac wouldn't boot), so I'm sending that pair back. The other pair works without obvious issue (thus far), but I ran two Rember cycles in Safe Boot, and got these errors on the first and second tests, respectively:

FAILURE! Data mismatch at local BUFA address 0x000000019a6e97b8, BUFB address 0x0000000879b9c7b8
BUFA Data: 0xffffffff80000000, BUFB Data: 0xffffffff80200000

FAILURE! Data mismatch at local BUFA address 0x000000060ffea7b8, BUFB address 0x0000000cbcbd47b8
BUFA Data: 0xd4d4d4d4d4f4d4d4, BUFB Data: 0xd4d4d4d4d4d4d4d4

Both tests also gave me the following error; I'm not sure of its significance—does this merely mean there's a risk of false negatives (missing a problem)? That wouldn't be an issue in this case, since a problem was detected. My concern is that it instead means there's a risk of false positives, i.e., that the above errors are not "real". Anyone understand Rember well enough to know whether it's the former or the latter?

Attempting memory lock... WARNING: Testing with unlocked memory may be slower and less reliable
ERROR: Memory lock failed - reason unknown.

Here's how they were configured—OWC recommends matching members of a pair be put into the same DIMM, so here they're both in DIMM0. Plus I found, from my own testing, that if you've got just one pair installed, they need to be in opposite channels to get full speed.

 

[DeltaMac]

Could you also try a test with MemTest?

MemTest86 - Official Site of the x86 Memory Testing Tool

MemTest86 is the original self booting memory testing software for x86 and ARM computers. Supporting both BIOS and UEFI, with options to boot from USB.

www.memtest86.com

Memtest boots your Mac, then runs the test. I think it prevents any kind of issue with software that is running in the background on your system, etc.

 

[theorist9]

Thanks, I flashed the drive and will let you know what I find.

 

[theorist9]

Could you also try a test with MemTest?

MemTest86 - Official Site of the x86 Memory Testing Tool

MemTest86 is the original self booting memory testing software for x86 and ARM computers. Supporting both BIOS and UEFI, with options to boot from USB.

www.memtest86.com

Memtest boots your Mac, then runs the test. I think it prevents any kind of issue with software that is running in the background on your system, etc.

I ran MemTest86 using the default configuration, except I stopped it after 2 passes, which took 13 hours. There were zero errors. What do I do now that I'm getting different results from MemTest86 and Rember?

According to the MemTest86 documentation, running one pass should be sufficient to detect 'all but the most obscure errors', suggesting that even two passes have a small chance of missing an error; thus it's possible the Rember results are legit (i.e., that my memory is bad, even if MemTest86 can't detect it).

After MemTest86 completed without errors, it suggested that I could run with Parallel CPUs* to increase my likelihood of detecting errors, but when I tried that I got the message that 'multi-CPU modes are unavailable due to UEFI firmware limitations'.

*I take that to mean MemTest86 uses only one CPU core when running the test, which makes sense, since I didn't hear the fans go on. Rember also uses only one core.

 

[DeltaMac]

I would note that MemTest86 has frequent updates, as late as last month.
Rember has not any update since 2010.
DDR4 RAM (and its supporting hardware) did not exist then.
I don't know if just using the application, testing hardware much newer than the app, would give you a good test.
Maybe, maybe not. How do you know? (I am not an expert on this, just asking the question)
Of course MemTest86 provides much more than just memory information, so would need to update when newer hardware versions (and new generations of chipsets, etc, are released for general use).
Which would you choose as your memory test source?

Maybe I am wrong in my reasoning. Maybe not.

 

[theorist9]

I would note that MemTest86 has frequent updates, as late as last month.
Rember has not any update since 2010.
DDR4 RAM (and its supporting hardware) did not exist then.

Good point.

Also asked this on the PassMark forums, will see what they say (will update this post with link when it becomes public).

Separately: MemTest86 gave me the CAS timing for my RAM: 19-19-19-43. I'm curious: Do you know if it was measuring the actual timing (like CPU-Z does), or just looking up the nominal timing associated with the part code?