Testing for RAM Errors w/ MemTest86

Windows7ge · January 22, 2021

What is MemTest86 and how does it work?

MemTest86 is an x86 based system memory (RAM) testing tool. Despite it's name and origin the latest free versions have compatibility with modern UEFI x64 based systems. What MemTest86 does is it uses a series of algorithms to write blocks of data to system memory then it reads those blocks back. If the data read matches what was written then the blocks pass. If the data read doesn't match what was written then an error was encountered. Under normal circumstances on a stable system no errors should be found but in the event of overclocking, hardware degradation, or DOA memory anywhere from a few to many errors can be encountered. How many errors are too many would have to be defined by how stable your computer is. If you're following this tutorial and fixing any errors you have makes your system stable again then you had too many.

How do I use it?

MemTest86 boots into it's own environment independent of your Operating System so you're going to need three tools:

A sacrificial thumb/flash/pen drive. NOTE: All pre-existing data on this drive will be erased!
MemTest86, the .ZIP of which can be downloaded from the official website: https://www.memtest86.com/
A means of writing the image file to your sacrificial drive the steps of which vary depending on your Operating System.

Installing the Image File to Your Drive

Spoiler

Setup on Windows

Spoiler

Start by extracting the contents of the .ZIP file to a folder on your desktop. Now connect your thumb drive and run the imageUSB.exe executable from the extracted folder. You'll be greeted by the following menu:

From here the steps are fairly self-explanatory:

Tick the box next to the drive you want to install MemTest86 to.
Choose the operation you wish to perform (default option is what we want)
Choose the image you want to write to the drive (default option should be memtest86-usb.img)
Click Write.

This will trigger a series of dialog boxes:

Verify that you've selected the correct drive (or just have your sacrificial drive be the only one connected - personal recommendation) and click Yes on both prompts.

From here wait patiently while the image is written to the drive.

After this a verification pass is done to ensure what was written is correct.

When you receive the following prompt MemTest86 was successfully installed and your bootable USB drive is ready for use:

Setup on GNU/Linux

Spoiler

Start by extracting the contents of the .ZIP file to a folder in your home directory. Now connect your thumb drive. First thing we need to do is identify what letter the drive was assigned by issuing the command:





lsblk

This will provide an output similar to the following:





NAME        MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
. . .
sdb           8:0    1  14.9G  0 disk 
└─sdb1        8:1    1  14.9G  0 part /media/username/1CCB-9A4A
nvme0n1     259:0    0   477G  0 disk 
├─nvme0n1p1 259:1    0   100M  0 part /boot/efi
├─nvme0n1p2 259:2    0    16M  0 part 
├─nvme0n1p3 259:3    0 237.9G  0 part 
├─nvme0n1p4 259:4    0   505M  0 part 
└─nvme0n1p5 259:5    0 238.5G  0 part /

Pay close attention to the SIZE column. Assuming your sacrificial drive is the only small USB storage device connected you'll find it easily here. In this instance our drive letter is sdb.

After you identify your drive you want to make sure it's not currently mounted. You can unmount any currently mounted partitions on the drive by issuing the command:





umount /dev/sdb*

Where "b" is the letter associated with your drive.

NOTE: This may give an error about certain secondary partitions not being mounted. This is fine.

From here format the drive into an appropriate File System. Typically EXT4:





sudo mkfs.ext4 /dev/sdb

Where "b" is the letter associated with your drive.

Now to write MemTest86 to our USB drive enter the folder containing our extracted files and issue the command:





sudo dd if=memtest86-usb.img of=/dev/sdb status=progress

Where "b" is the letter associated with your drive.

When the write operation completes your bootable USB is ready to go.

Setup on MacOS

Spoiler

Start by extracting the contents of the .ZIP file to a folder in your users directory. Now connect your thumb drive. First thing we need to do is identify what letter the drive was assigned by issuing the command:





diskutil list

Pay close attention to the SIZE column. Assuming your sacrificial drive is the only small USB storage device connected you'll find it easily here.

After you identify your drive you want to make sure it's not currently mounted. You can unmount the drive by issuing the command:





diskutil unmountDisk /dev/disk#

Where # is the number associated with your drive.

Now to write MemTest86 to our USB drive enter the folder containing our extracted files and issue the command:





sudo dd if=memtest86-usb.img of=/dev/disk# status=progress

Where # is the number associated with your drive.

When the write operation completes your bootable USB is ready to go.

Running MemTest86

Connect your MemTest86 drive to the suspect computer and turn it on. Now booting to a USB drive may not be set as a higher priority than your default boot drive or be set at all. In either case you may have to enter your BIOS and manually select the USB drive to be booted first in the Boot Priority menu. Alternatively many BIOS's support a Boot Override menu via F10 or F11 at startup. Some even support boot override from within the BIOS menu itself.

Once you successfully boot to the USB drive the first thing MemTest86 will do is start querying the system for information:

Retrieving hardware info. Please wait...
Getting CPUID info...
Getting cache size...
Measuring CPU/cache/mem speeds...
Retrieving CPU MSR data...
Getting SPD details...
Getting memory controller details...
Testing multiprocessor support...

After this you'll be shown a splash-screen:

From here to run a simple memory test wait for the timer denoted above to expire and a test will begin automatically:

At this stage allow the test to run to completion. How long the test will take is proportional to how much RAM you have. The more RAM the longer you will have to wait.

When the test finishes MemTest86 will bring you to a results page to show you what errors it found if any. If you do have errors there are multiple approaches to troubleshooting them. Most methods are easy but there are progressively more difficult steps if initial troubleshooting doesn't yield results.

Easy Troubleshooting Steps

Disable X.M.P./D.O.C.P.
Re-seat the memory.
Swap the memory around in their slots.
Remove a stick entirely and re-test.

Intermediate Troubleshooting Steps

Loosening RAM timing/frequency manually.
Replacing RAM entirely.

Difficult Troubleshooting Steps

Testing a different motherboard
Testing a different PSU
Testing a different CPU

Closing Thoughts

MemTest86 is a very powerful tool for recognizing memory errors when troubleshooting an unstable computer. It's worth keeping in your pocket if you work on systems regularly. It's also worth noting that MemTest86 and it's fork MemTest86+ may not find errors on the first pass. You may need to run it more than once before it picks something up.