Testing your memory configuration to verify stability
Before you decide that this section is not worth your time or get lazy thinking you don't need to test because you you're system "seems" fine, with no obvious blue screens, freezing or restarting, let me make one thing VERY, VERY CLEAR.
ANY amount of instability in your memory configuration is enough to cause what are known as micro errors. This is a very miniscule error which, if it only happened one time might not ever be a factor but when it happens incrementally over time, can result in complete and total corruption of your operating system, documents, game files, applications, music, movies, everything, to the point of being a complete and total loss with no chance of recovery.
Memory configurations that are not as close to 100% stable as possible are not a joke. They WILL eventually cause widespread corruption of the entire file system. Don't cut corners because it's simply not worth it. If you are unwilling to do the testing necessary to make sure the system is stable you should simply leave the memory at the default configuration and that includes NOT setting the memory to the XMP profile if the profile of the memory is beyond what the system automatically configures the memory speed and timings to by default. Do the testing. One day out of your life is not going to kill you but not doing it might make you wish you had died if you lose a lot of very important information and personal files that can't be replaced.
Memtest86
Go to the Passmark software website and download the USB Memtest86 free version. You can do the optical disk version too if for some reason you cannot use a bootable USB flash drive.
Create bootable media using the downloaded Memtest86 (NOT Memtest86+, that is a different, older version and is outdated). Once you have done that, go into your BIOS and configure the system to boot to the USB drive that contains the Memtest86 USB media or the optical drive if using that option.
Click here to download Memtest86 USB package
Create a bootable USB Flash drive:
1. Download the Windows MemTest86 USB image.
2. Right click on the downloaded file and select the "Extract to Here" option. This places the USB image and imaging tool into the current folder.
3. Run the included imageUSB tool, it should already have the image file selected and you just need to choose which connected USB drive to turn into a bootable drive. Note that this will erase all data on the drive.
No memory should ever fail to pass Memtest86 when it is at the default configuration that the system sets it at when you start out or do a clear CMOS by removing the CMOS battery for five minutes.
Best method for testing memory is to first run four passes of Memtest86, all 11 tests, WITH the memory at the default configuration. This should be done BEFORE setting the memory to the XMP profile settings. The paid version has 13 tests but the free version only has tests 1-10 and test 13. So run full passes of all 11 tests. Be sure to download the latest version of Memtest86. Memtest86+ has not been updated in MANY years. It is NO-WISE as good as regular Memtest86 from Passmark software.
If there are ANY errors, at all, then the memory configuration is not stable. Bumping the DRAM voltage up slightly may resolve that OR you may need to make adjustments to the primary timings. There are very few secondary or tertiary timings that should be altered. I can tell you about those if you are trying to tighten your memory timings.
If you cannot pass Memtest86 with the memory at the XMP configuration settings then I would recommend restoring the memory to the default JEDEC SPD of 1333/2133mhz (Depending on your platform and memory type) with everything left on the auto/default configuration and running Memtest86 over again. If it completes the four full passes without error you can try again with the XMP settings but first try bumping the DRAM voltage up once again by whatever small increment the motherboard will allow you to increase it by. If it passes, great, move on to the Prime95 testing.
If it still fails, try once again bumping the voltage if you are still within the maximum allowable voltage for your memory type and test again. If it still fails, you are likely going to need more advanced help with configuring your primary timings and should return the memory to the default configuration until you can sort it out.
If the memory will not pass Memtest86 for four passes when it IS at the stock default non-XMP configuration, even after a minor bump in voltage, then there is likely something physically wrong with one or more of the memory modules and I'd recommend running Memtest on each individual module, separately, to determine which module is causing the issue. If you find a single module that is faulty you should contact the seller or the memory manufacturer and have them replace the memory as a SET. Memory comes matched for a reason as I made clear earlier and if you let them replace only one module rather than the entire set you are back to using unmatched memory which is an open door for problems with incompatible memory.
Be aware that you SHOULD run Memtest86 to test the memory at the default, non-XMP or custom profile settings BEFORE ever making any changes to the memory configuration so that you will know if the problem is a setting or is a physical problem with the memory.
After your memory will pass Memtest for 4 full passes, it is still not necessarily stable, but it is a good start and you should move on the the last phase of testing using Prime95. See, there IS a light at the end of the tunnel.
Final testing with Prime95
It is highly advisable that you do a final test using Prime95 version 26.6 (And ONLY version 26.6 except as noted below) choosing the Custom test. You can also use the Blend mode option but after a fair amount of personal testing, asking questions from some long time members with engineering level degrees that have forgotten more about memory architectures than you or I will ever know, and gathering opinions from a wide array of memory enthusiasts around the web, I'm pretty confident that the custom option is a lot more likely to find errors with the memory configuration, and faster, if there are any to be found.
Please note as this is rather important, if you prefer, or have problems running version 26.6 because you have a newer platform that doesn't want to play nice with version 26.6, you can use the latest version of Prime95 with the Custom test selected but you will need to make the following change.
If you wish to use a newer version than 26.6 make the following edit to the "local.txt" file located in the Prime95 folder.
Find the line value that specifies CpuSupportsAVX=1, and change it to CpuSupportsAVX=0
Then click File-->Save, and then close the document.
Now open Prime95.
Click on "Custom". Input a value of 512k in the minimum FFT size field. Leave the maximum FFT size field at 4096k. In the "Memory to use" field you should take a look at your current memory allocation in either HWinfo or system resource monitor. Whatever "free" memory is available, input approximately 75% of that amount. So if you currently have 16GB of installed memory, and approximately 3GB are in use or reserved leaving somewhere in the neighborhood of 13GB free, then enter something close to 75% of that amount.
So if you have 13GB free, or something reasonably close to that, then 75% of THAT would be 9.75GB, which, when multiplies times 1024 will roughly equal about 9984MB. You can average things out by simply selecting the closest multiple of 1024 to that amount just to keep it simple, so we'll say 10 x 1024= 10240mb and enter that amount in the field for "Memory to use (MB)". We are still well within the 13GB of unused memory BUT we have left enough memory unused so that if Windows decides to load some other process or background program, or an already loaded one suddenly needs more, we won't run into a situation where the system errors out due to lack of memory because we've dedicated it all to testing.
I've experienced false errors and system freezes during this test from over allocating memory, so stick to the method above and you should be ok.
Moving right along, do not change the time to run each FFT size.Leave that set to 15 minutes.
Click run and run the Custom test for 8 hours. If it passed Memtest86 and it passes 8 hours of the Custom test, the memory is 100% stable, or as close to it as you are ever likely to get but a lot of experts in the area of memory configuration suggest that running the extended Windows memory diagnostic test is also a pretty good idea too.
If you get errors, (and you will want to run HWinfo alongside Prime95 so you can periodically monitor each thread as Prime will not stop running just because one worker drops out, so you need to watch HWinfo to see if there are any threads not showing 100% usage which means one of the workers errored and was dropped) then you need to either change the timings, change the DRAM voltage or change the DRAM termination voltage, which should be approximately half of the full DRAM voltage.
There are also other bios settings that can affect the memory configuration AND stability, such as the VCCIO and system agent voltages, so if you have problems with stability at higher clock speeds you might want to look at increasing those slightly. Usually, for Intel at least, something in the neighborhood of 1.1v on both those is pretty safe. There are a substantial number of guides out there covering those two settings, but most of them are found within CPU overclocking guides so look there in guides relevant to your platform.
As a further measure of assurance that your WHOLE configuration is stable, you can download and run Realbench for 8 hours. If the system freezes or fails when running Realbench with your full memory amount set, try running it again but select only half your amount of installed memory.
Hopefully by now you have memory that is working correctly, in the full amount you purchased, and at the advertised speed and timings. I am certainly no expert in the area of memory architectures or very advanced configurations, but hopefully this has helped you to some degree and if there are questions I might be able to answer that were not addressed here, feel free to start a thread and PM me with a link to your question. Good luck and happy gaming, or whatever it is you do on your machine.
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