MemTest86 USB won't boot

[ratkindler]

I've got two laptops I'd like to test the memory for: one is an older Windows 7 system (now with Windows 10) and a legacy BIOS and the other is a new system. MemTest86 boots on the new system in both UEFI and legacy BIOS modes, while the older system doesn't see the USB to boot from it for some reason. I've noticed that the new system sees both partitions on the USB as separate drives, while my older system only sees just one (presumably the UEFI partition). Anyone have some suggestions as to how I can get my older system to boot from the legacy BIOS partition for MemTest86?

Also, I ran both MemTest86 v.4 (legacy BIOS version) and the newest version (UEFI) on my new system and v.4 gave over 500 errors with 4 passes, while the UEFI version gave just 6 errors on test #10. Further, when I ran it again it gave NO errors at all. I'm not sure what to make of these inconsistent results between tests! What does it mean?

[David (PassMark)]

the new system sees both partitions on the USB as separate drives

This is normal. The extra partition is for compatibility with a wider range of systems.

On the MemTest86 download page there is a package with just V4 in it.

I'm not sure what to make of these inconsistent results

Might be just different memory addresses being tested, or maybe something else (like the problem being intermittent).
If this behaviour reproducible? Are the 500 errors in a small range of memory addresses?
Is V7 running in multi-threaded mode, or only on 1 core?

[ratkindler]

Still haven't been able to get my old system to boot the V4 USB. Not sure what to do next.

As for my new system that has been experiencing daily BSOD reboots, I don't remember what the memory addresses in error were. I just ran the latest MemTest for 20 hours (8 passes) in single CPU (0) mode and it didn't find anything. When using all 4 CPUs MemTest crashes - interestingly, it also crashes if using just 1 CPU if it's anything other than 0.

So I still don't know if my RAM needs to be replaced since sometimes there are errors but with the recent 8 passes there were none.

[David (PassMark)]

When using all 4 CPUs MemTest crashes - interestingly, it also crashes if using just 1 CPU if it's anything other than 0.

Likely this is a UEFI BIOS bug. See,
List of Motherboards with issues when running MemTest86 in multi-CPU selection modes

Maybe the older system never supported booting from a USB drive. You might need to use a CD boot.