How to Use MemTest86 to Test RAM in Under 10 Minutes
Learning how to use MemTest86 is one of the fastest ways to check your RAM for errors, since it runs outside your operating system entirely. You boot it from a USB drive, let it write and read patterns across every memory address, and it flags anything that doesn’t come back correct. It’s the standard first step when your PC crashes randomly, blue screens, or feels unstable after a RAM upgrade or overclock.
Table of Contents
How to Use MemTest86- Quick Answer
| Step 1 | Download MemTest86 from the official PassMark site and create a bootable USB drive with the included imageUSB tool (or Rufus). |
| Step 2 | Restart your PC, press your boot menu key (F12, F11, F10, or Del depending on brand), and select the USB drive. |
| Step 3 | Let MemTest86 run automatically. The default is 4 passes, which covers most systems. Run it longer overnight if you suspect an intermittent fault. |
| Step 4 | Any red “errors found” means bad RAM or a bad slot. Zero errors after multiple passes means your RAM is very likely healthy. |
Is MemTest86 Safe?
Yes. MemTest86 is made by PassMark, the same company behind PerformanceTest and other well-known benchmarking software, and it only reads and writes to RAM, not your hard drive or SSD. It can’t damage your storage or install anything on your operating system because it never touches Windows at all, it boots completely outside of it. The free edition is the one most people need. The only real risk is on the setup side, since building the bootable USB will erase everything currently on that drive, so back up any files on it first.
If your PC feels unstable and you’re not sure whether it’s a CPU or GPU bottleneck or an actual hardware fault, a MemTest86 RAM test is one of the safest ways to rule bad memory in or out before you start swapping parts.
What You Need Before You Start
- A USB flash drive, at least 512MB (a 2GB+ drive is safest for newer versions)
- A working computer to create the bootable drive
- Access to your PC’s BIOS/UEFI boot menu
How to Create a Bootable MemTest86 USB Drive
Head to the official MemTest86 download page and grab the free USB version. Once it’s downloaded:
- Extract the zip file into its own folder.
- Plug in your USB drive. Remember, it gets wiped completely.
- Open imageUSB.exe from the extracted folder.
- Select your USB drive, make sure “Write image to USB drive” is selected along with the included memtest86-usb.img file, then click Write.
- Confirm the warning prompts. Writing usually takes a few minutes.
You can also use Rufus if you prefer, just point it at the same image file. Either way, once the drive finishes writing, it’s ready to boot. Corsair’s official memory testing walkthrough follows this exact same imageUSB process and is a good visual reference if you get stuck on any screen.
How to Run MemTest86 from BIOS
With the USB drive plugged in, restart your PC and press your motherboard’s boot menu key repeatedly as it powers on. This pulls up a one-time boot device list without changing your permanent boot order in BIOS.
| Motherboard Brand | Boot Menu Key |
|---|---|
| ASUS | F8 |
| Gigabyte | F12 |
| MSI | F11 |
| ASRock | F11 |
| Dell / HP / Lenovo (laptops) | F12 or Esc |
Select your USB drive from the list, ideally the entry labeled “UEFI: [your drive name]” if you see two versions listed. MemTest86 should load automatically and begin the RAM test on its own within a few seconds. Some builders also clear CMOS to factory defaults before testing, since leftover overclock or XMP tweaks in BIOS can cause errors that aren’t actually about the RAM hardware itself.
How to Run MemTest86 Windows 11
Windows 11 systems almost always run in UEFI mode with Secure Boot turned on, and that combination is the most common reason people get stuck at this step. MemTest86’s current versions boot in UEFI mode, so this normally isn’t an issue, but if your USB drive doesn’t show up in the boot menu or the system skips straight past it, try this order:
- Turn off Fast Startup in Windows before you reboot (Control Panel > Power Options > Choose what the power buttons do). Fast Startup can prevent a full shutdown and interferes with boot menu access.
- If the drive still isn’t detected, temporarily disable Secure Boot in BIOS/UEFI settings, boot MemTest86, then re-enable it afterward.
- Double check the boot mode matches. A USB written for UEFI won’t show up if your board is set to Legacy/CSM mode, and vice versa.
Running the MemTest86 RAM Test: How Many Passes Do You Need
Once it boots, MemTest86 starts testing automatically using its default test suite. You’ll see a progress bar, the pass count, and a running error tally at the top of the screen.
- Quick check: 1-2 passes will catch obvious, serious RAM failures. Takes roughly 20 minutes to an hour depending on your RAM capacity and speed.
- Thorough check: The default 4-pass setting runs the complete testing algorithm across all your memory and is enough for most systems. Bump it up to 8+ passes overnight if you’re chasing an intermittent issue tied to heat or a specific workload.
If you’re testing RAM you just bought after reading through our DDR4 vs DDR5 or best RAM for gaming picks, a clean overnight MemTest86 run is the easiest way to confirm the new kit is stable before you build the rest of your settings around it.
Reading Your MemTest86 Results
If the error count stays at zero through multiple full passes, your RAM is very likely fine, and any crashes you’re seeing point elsewhere, worth checking against a thermal throttling issue or a CPU/GPU bottleneck instead. If MemTest86 flags any errors at all, even one, treat that RAM stick as suspect. There’s no “acceptable” number of errors.
What to Do If MemTest86 Finds Errors
- Reseat the RAM sticks fully and make sure they’re in the correct slots per your motherboard manual.
- Test one stick at a time to isolate whether it’s a specific module or a specific slot causing the errors.
- If you’re running XMP or EXPO overclocked speeds, reset to default JEDEC speeds and retest. Overclocked RAM that isn’t fully stable is a common source of false “bad RAM” errors.
- If a single stick consistently errors out in multiple slots, it’s faulty and should be replaced or RMA’d.
FAQ
Should I use MemTest86 or MemTest86+?
Go with MemTest86 (no plus). It’s the actively maintained version from PassMark with full UEFI and Secure Boot support. MemTest86+ is a separate open-source fork that hasn’t seen regular updates in years and has caused confusion in forums for over a decade, including recurring questions on Slackware and Proxmox community threads about which one actually works on modern boards.
How many passes does MemTest86 actually need?
According to discussion on PassMark’s own support forum, the default of 4 passes is enough for testing RAM in most systems and runs the full suite of test algorithms across all memory. Users chasing intermittent faults tied to heat or electrical interference sometimes bump that up manually.
MemTest86 seems stuck or frozen, is that normal?
Occasional hangs have been reported by users, particularly on higher-end or newer systems, according to discussions on tech forums like Wilders Security. If it looks frozen, give it a few extra minutes since large RAM capacities take longer per pass. If it’s truly locked up with no progress at all, reboot, rewrite the USB drive, and try again.
MemTest86 isn’t detecting my USB drive, what’s wrong?
This is almost always a boot-mode mismatch. A USB drive written for UEFI boot won’t show up if your motherboard is set to Legacy/CSM mode, and the reverse is also true. Secure Boot can also block it if it’s enabled. Check that your boot mode setting matches how the USB was written, and confirm the drive is prioritized in your boot order.
My PC won’t boot normally after running MemTest86, did it break something?
This has come up on PassMark’s own user forum, where someone’s PC failed to display anything after exiting MemTest86 with the USB drive still plugged in. In most of these cases the fix is simply removing the USB drive before restarting and double-checking the boot order in BIOS, since MemTest86 itself doesn’t write to or modify your system drive.
Can I run a MemTest86 RAM test without creating a USB drive?
Not for the full diagnostic. MemTest86 has to run outside your operating system to test all of your RAM, including the portion Windows normally reserves for itself. A CD/DVD works too if your PC still has an optical drive, but USB is faster and far more common today.
Conclusion
Now that you know how to use MemTest86, you’ve got one of the most reliable ways to rule bad RAM in or out. Run at least 2-4 passes for a quick check, or let it go overnight if a crash is proving hard to pin down. If it comes back clean, don’t stop there, since some stutter and crash issues that feel like bad RAM are actually a CPU or GPU bottleneck in disguise. Run your specs through the bottleneck calculator to see which one you’re really dealing with.
