My experience with MemTest86 - great piece of software!

[Ultima Gaina]

I just built a new desktop based on:
AMD Ryzen Thredripper 2950X processor
ASUS Prime X399-A motherboard,
64GB of Corsair Dominator Platinium 3000MHz DDR4 (4x 16GB modules)

My new PC froze twice when engaged in heavy processing using more than 32GB of RAM and I got worried.
Did some research and found this great piece of software called MemTest86.

I ran the test the whole night and here is what I found:


As you can see, not very encouraging results: 15 errors after 4 passes and over 10 hours of tests.

I ran the same test again and I got errors again, although not exactly the same.

Here is the summary:


So I decided to test one RAM module at the time, running only once the tests with errors (3,4,5,7,, to speed up the troubleshooting
The result was that 3 modules (out of 4) showed no errors, while the fourth gave me errors, but not not always. After running the test again, even this one came clean. Somehow confusing.

This why I decided to go for a 3rd round of tests, paring two modules together, in 32GB batches

Maybe not surprisingly, the only time I got errors was when the module I already suspected as faulty was part of the mix.

I removed the faulty module and plugged the remaining 3 (48GB in total) and ran the whole sequence again (all tests, 4 passes)
Guess what? NO errors! Yesss!

I called Amazon support and they are sending me overnight, no charges, another 32GB kit.

Will be testing again tonight, but I have a strong feeling that everything will be all right, tonight!

Thanks Memtest86!

[David (PassMark)]

Thanks for the positive feedback.

It is fairly common to see differences in behaviour between testing 1 stick and 2 sticks. As with two sticks the memory is placed into dual channel mode and the timings change.

[Ultima Gaina]

I got the kit with the two additional sticks yesterday and ran all the tests (4 passes, >10 hours) throughout the night.
I'm happy to report no errors found and all my RAM works fine in quad mode!

David, if you don't mind, I have just one additional clarification.
I'm not planing to do it, just for the sake of it: if I add the additional good working 16GB stick to the existing quad 64GB, that one isolated stick will work in single mode. But when will that additional 16GB of memory be addressed? Is it the last resort, in other words will it be used only when the quad 64GB is exhausted, or it will be randomly addressed, leading to lower performance, when it happens?
Thanks!

[David (PassMark)]

The Ryzen 2950X is a quad channel CPU. So using 5 sticks will results in that one extra module being put into single channel mode (assuming that this is a supported configuration of the motherboard & CPU).

[Ultima Gaina]

Yes, I understand it David. CPU-Z shows the 64GB used in quad configuration, indeed.

The question I have is about when will that extra single 16GB be used.
Is it only when the quad 64GB part of the memory is fully utilised or just randomly?
Because if it is just randomly, having the extra single stick might actually lower the performance for apps using only a part of the total Ram available.

Sorry if I didn't make myself clear.

[David (PassMark)]

It won't be random. But it will be hard to find the answer. The question is really: Where will the extra physical memory be placed into the memory map. At the start, at the end, or interleaved in the middle. Could even be the case that the other 4 sticks fall out of quad channel mode and they all run single channel. Then the next question is how do the applications that you use (and the operating system) allocate their RAM and are they likely to use the additional addresses first or last.

There is an answer, but it will vary by platform, and I don't know what that answer is.

[Ultima Gaina]

Thanks David. From what I read and understand, it is very likely that adding a single stick (or maybe even two, in dual mode) to an already working quad configuration might cancel, sometimes, the benefits of the quad configuration. Probably, the next upgrade step should be straight to 128GB, by adding another quad set to the system.