To test RAM for errors, create a bootable MemTest86 USB drive, boot from it before Windows loads, and let it run at least one full pass, which typically takes a few hours depending on your RAM size. Any errors reported point to a faulty stick, a bad slot, or an unstable overclock.
- MemTest86 runs outside Windows, testing RAM directly.
- Let it complete at least one full pass before judging results.
- Any errors shown mean something needs fixing or replacing.
- Test one stick at a time to isolate which one is faulty.
When to Test Your RAM
- Random crashes, blue screens, or freezes with no obvious cause
- After enabling XMP or an overclock, to confirm stability
- After installing new RAM, before trusting it with real work
- Buying a used PC or used RAM sticks with unknown history
How to Run MemTest86
1. Download MemTest86
Get it from the official MemTest86 site, which offers a free version suitable for most home testing needs. Tom’s Hardware also covers the process with screenshots if you want a second reference.
2. Create a bootable USB drive
Use the included tool to write MemTest86 to a USB drive, which erases anything already on it, so use a spare or empty drive.
3. Boot from the USB drive
Restart the PC and enter the boot menu, usually by pressing F11 or F12 during startup, then select the USB drive to boot from it directly.
4. Let it run
MemTest86 starts automatically and begins its first pass. Let it run uninterrupted, ideally for at least one full pass, which can take anywhere from 30 minutes to several hours depending on how much RAM you have.
5. Read the results
A clean pass with zero errors, similar to the guidance in Crucial’s RAM testing guide, is a good sign. Any errors listed point to a problem, and the tool often narrows down which memory address, and therefore roughly which stick, is affected.
If Errors Show Up
- Power off and test one stick at a time in a single slot to isolate which stick is faulty.
- If you recently enabled XMP or overclocked, return to stock settings and retest, since instability there can look identical to a hardware fault.
- Reseat the stick and try a different slot before assuming it’s dead.
- If a specific stick fails consistently across slots, it’s likely faulty and should be replaced, often under warranty.
Note: a single pass with no errors is a reasonable confidence check for everyday use, but running two or more passes overnight gives a more thorough result if you suspect an intermittent problem.
Checking Your RAM First
Before testing, confirm your exact installed RAM with what RAM do I have, and if you suspect a mismatch is the cause, see do RAM sticks have to match.
Windows’ Built-In Alternative
Windows includes its own Memory Diagnostic tool, accessible by searching “Windows Memory Diagnostic” in the Start menu. It’s faster and easier to run than MemTest86 but generally less thorough, making it a reasonable quick check rather than a full replacement.
Frequently Asked Questions
How long does MemTest86 take?
A full pass typically takes 30 minutes to a few hours depending on how much RAM is installed. Running overnight is common for a thorough check.
Is MemTest86 safe to use?
Yes. It only reads and writes test patterns to memory and does not modify your operating system or files.
Does MemTest86 tell me which stick is bad?
It reports the memory address where an error occurred, which helps narrow things down, but testing sticks individually in a single slot gives the clearest answer.
Can RAM pass MemTest86 and still be bad?
It’s possible for intermittent issues to not show up in a short test. Running multiple passes over a longer period improves the chance of catching an inconsistent fault.
