How to Test Your Computer’s RAM for Errors Using Memtest86

To test your PC’s RAM for errors, download the free version of MemTest86, write it to a USB flash drive with the included imageUSB tool, boot from that USB, and let MemTest86 run at least 2–4 full passes. If errors appear, remove all but one RAM stick and re-test each one individually in each slot to isolate whether the stick or the slot is faulty. Skip Windows Memory Diagnostic — it misses subtle errors that MemTest86 catches.

Applies to: MemTest86 v11 (free) on Windows 10 (22H2) and Windows 11 (23H2, 24H2, 25H2), UEFI and legacy BIOS systems | Last updated: April 17, 2026

Key Takeaways

• MemTest86 runs outside Windows — it boots directly from a USB stick, so it can exercise every byte of RAM without the OS holding part of it in reserve.
• Use the free v11 build for modern UEFI PCs, v4 for legacy BIOS systems — both are free, both are at memtest86.com. Do not confuse MemTest86 (PassMark) with MemTest86+ (a fork).
• Run at least 2 full passes, ideally 4 — intermittent errors often only show up after several passes. A full pass on 16–32 GB takes roughly 30–60 minutes.
• Any non-zero error count means that RAM configuration is faulty — shutdown, remove all but one stick, and test each one individually to pinpoint which stick or slot is bad.
• Windows Memory Diagnostic (mdsched) is not a substitute — in my repair shop I regularly see sticks that pass Windows Diagnostic but fail MemTest86 within one pass.

Quick Steps

1. Download MemTest86 v11 (UEFI) or v4 (legacy BIOS) from memtest86.com.
2. Extract the ZIP and run imageUSB.exe. Plug in a USB stick (4 GB+) — it will be erased.
3. Select the USB drive, confirm Write image to USB drive, click Write.
4. Restart the PC, open the boot menu (usually F12, F11, or Esc at power-on), and boot from the USB.
5. Let MemTest86 run — 2 full passes minimum, 4 passes for a thorough test. Walk away.
6. Read the pass/fail summary at the end. Any error = faulty RAM or slot; swap sticks and re-test to isolate.

Why Use MemTest86 Instead of Windows Memory Diagnostic

Windows ships with its own memory tester (mdsched.exe, the “Windows Memory Diagnostic” tool). It sounds like the obvious choice, but in my repair shop I have pulled sticks that produced zero errors in Windows Memory Diagnostic and then failed MemTest86 within the first pass. The Windows tool is fast but shallow — it runs a short series of patterns and declares the RAM fine.

MemTest86 runs a much deeper set of tests: moving inversions, address tests, walking-bit patterns, bit-fade, random number, hammer tests, and more. It exercises every byte of installed RAM — not just the portion the running OS happens to have free — and it runs outside Windows, so no paging, no caching, no interference. That is why every PC repair technician I know runs MemTest86 for memory faults, not the built-in tool.

Faulty RAM shows up as random BSODs, stop codes like MEMORY_MANAGEMENT or IRQL_NOT_LESS_OR_EQUAL, file-corruption after saves, games crashing to desktop, and intermittent boot failures. If you are seeing any of those symptoms, MemTest86 is the first diagnostic to run before you replace anything.

Download MemTest86 (Free Version)

Head to memtest86.com and find the Free Edition download section. There are two relevant builds:

• MemTest86 v11 (current) — UEFI boot only. This is what the vast majority of PCs built after 2013 need.
• MemTest86 v4 — legacy BIOS boot. Use this only if your motherboard does not support UEFI (pre-2012-era systems).

If you are not sure which to grab, start with v11 — if it refuses to boot and your firmware is legacy-BIOS only, fall back to v4. Both are distributed as ZIP archives containing the bootable image plus imageUSB.exe, the utility PassMark uses to write the image to a flash drive.

Write MemTest86 to a USB Flash Drive

You need a USB flash drive with at least 4 GB of space. The drive will be wiped, so back up anything on it first.

1. Right-click the downloaded ZIP and choose Extract All.
2. Open the extracted folder and double-click imageUSB.exe.
3. In Step 1, select the target USB drive from the list.
4. In Step 2, make sure Write image to USB drive is selected.
5. In Step 3, verify the .img file is pre-selected (it should be, from the same folder).
6. Click Write. Confirm the format warning and wait for the write to finish.

Alternative: If you already have Ventoy on a USB, drop the MemTest86 ISO into the Ventoy partition instead — no dedicated stick required.

Boot from the USB and Run MemTest86

With the USB written, shut down the PC you want to test and plug the stick in.

1. Power the PC on and immediately hit the boot-menu key. Most common: F12 (Dell, Lenovo, HP desktops), F11 (MSI, ASRock), F9 (HP laptops), or Esc (some HP/Acer). If you miss it, just restart and try again.
2. In the boot menu, select the USB drive (UEFI entries are prefixed with UEFI:). If you installed v11 and nothing UEFI-labelled appears, see the troubleshooting section below.
3. MemTest86 boots into its menu. You can press Enter to use defaults — testing starts automatically after a 10-second countdown.
4. Let it run. One full pass cycles through every test type once. Minimum: 2 passes. Recommended: 4 passes for a thorough check.

You can walk away — MemTest86 runs without supervision and stores all results on the USB. When all configured passes complete, it shows a green PASS or a red FAIL summary screen and writes an HTML report to the USB’s root directory.

Interpret the Results and Isolate a Bad Stick

At the end of the run you will see one of three outcomes:

• PASS, 0 errors — all installed RAM passed every test pattern. Your memory is not the fault.
• FAIL with errors listed on specific test numbers — one or more RAM sticks is faulty, or one of your RAM slots is bad.
• System hangs or reboots mid-test — almost always a hardware issue in RAM, the motherboard memory controller, or the CPU’s integrated memory controller.

If you see errors, do not swap the whole kit out yet — isolate first:

1. Power off. Remove all RAM sticks except one.
2. Re-run MemTest86 with that single stick. One pass is usually enough to see if it fails.
3. If it passes, swap to the next stick. Repeat until each stick has been tested.
4. If every stick passes individually, re-test pairs in different slot combinations. A single bad slot on the motherboard is uncommon but does happen — I see maybe one per 50 bad-RAM cases at the repair bench.

Once you have identified the faulty stick (or slot), mark it and remove it from the system. If it is under warranty, most RAM is lifetime-warrantied — Corsair, Kingston, Crucial, and G.Skill will RMA a stick that fails MemTest86 as long as you did not overclock beyond its rated spec. For replacement ideas, see my best RAM for gaming guide.

Troubleshooting: MemTest86 Won’t Boot

• No USB entry in the boot menu — some firmware hides USB entries unless Secure Boot is disabled. Enter the BIOS/UEFI setup and temporarily disable Secure Boot; you can turn it back on afterwards.
• USB shows but refuses to boot — your system may be legacy-BIOS only. Re-download MemTest86 v4 and rewrite the USB with that instead.
• PC boots into Windows instead of USB — Fast Boot is enabled. Hold Shift while clicking Restart in Windows, then choose Use a device → UEFI USB to force a USB boot. Longer term, disable Fast Boot in BIOS.
• Not sure whether you need UEFI or legacy — my select the correct boot mode section explains how to identify it from Windows.

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Frequently Asked Questions

How long does MemTest86 take to finish?

One full pass on 16 GB of DDR4 takes roughly 30–45 minutes. 32 GB is about an hour. 64 GB is 90+ minutes. Four passes (the thorough-test target) scales linearly — budget 2–6 hours depending on capacity. MemTest86 runs unattended, so start it overnight if your RAM is large.

Can I use Windows Memory Diagnostic instead?

You can, but it is much less thorough. Windows Memory Diagnostic catches obvious hard failures but regularly misses intermittent or pattern-specific errors that MemTest86 picks up in the first pass. If you genuinely suspect RAM, use MemTest86 — skipping straight to the deeper test saves time.

What do I do if MemTest86 reports errors?

Shut down, remove all sticks except one, and re-test each stick individually. This tells you whether one specific stick is faulty. If every stick passes alone, re-test pairs in different slot combinations — occasionally a single motherboard RAM slot is the fault, not a stick. Once you have isolated the bad component, RMA the RAM under warranty or replace the affected hardware.

Can MemTest86 fix bad RAM?

No. MemTest86 only diagnoses. Bad RAM is a hardware failure — there is no software fix. The only remedies are RMA under warranty or replacement.

Is the free MemTest86 version enough, or do I need the paid Pro edition?

For home diagnostics, the free edition is everything you need — all 13 test patterns, full reporting, and unlimited passes. The paid Pro edition adds enterprise features like config-file scripting, PXE network booting, and deeper reporting — useful for IT fleets, not home users.