memtest86+

Bootable Memory Diagnostic

Bootable (x86/x64) GPLv2

What It Does

memtest86+ is an open-source, standalone memory testing program that boots directly from USB or CD — no operating system required. It writes test patterns to every address in RAM, reads them back, and reports any mismatches. If your system has random crashes, blue screens, or data corruption, memtest86+ is how you confirm whether the RAM is the problem.

Why You Need It

Bad RAM is one of the hardest failures to diagnose because the symptoms mimic dozens of other problems — random BSODs, application crashes, corrupted files, failed installs. A memory test removes the guesswork. It is one of the first tools to reach for when a system is unstable. Referenced in:

SG-31 — Build a Bootable USB Drive (Field Prep)

CompTIA A+ explicitly covers memory troubleshooting and diagnostic tools. Having memtest86+ on a bootable USB is a baseline expectation for any IT technician.

How to Install It

Download the latest release from memtest.org (look for the USB installer package or ISO).
USB method (recommended): Download the USB installer (.zip), extract it, plug in a USB drive (512 MB is plenty), and run the included installer script. On Windows this is an .exe; on Linux, use dd:
```
sudo dd if=memtest86+-7.00.img of=/dev/sdX bs=1M status=progress
```
Replace /dev/sdX with your USB device. Double-check the device — dd will overwrite without confirmation.
ISO method: Download the ISO and burn it using Rufus, Etcher, or your preferred tool.
Boot the target machine from the USB. Access the boot menu during POST (F12, F2, or Esc depending on manufacturer).

How to Use It

1. Boot and let it run

Once booted, memtest86+ starts testing immediately with no user interaction required. The screen shows a blue interface with test progress, pass count, and error count. Each pass is a full cycle through all test patterns across all memory addresses.

2. Understand the display

Pass: How many complete test cycles have finished. You want at least 2 full passes for basic confidence.
Test: Which of the 13 test algorithms is currently running (e.g., moving inversions, block move, random pattern).
Error Count: Number of mismatches found. Even one error means the RAM stick is bad.
Error Address: The physical memory address where the failure occurred. This helps identify which DIMM slot is affected.

3. How long to run

A minimum of 2 full passes is standard for a quick check (typically 30-60 minutes for 16 GB). For thorough testing — especially intermittent issues — run it for 4-8 hours or overnight. Some memory errors only appear when the hardware heats up, so longer runs catch thermal-related failures.

4. Interpret errors

If errors appear, note the failing address range. Remove one stick at a time and retest to isolate the bad module. If errors persist with every individual stick, the problem may be the motherboard's memory controller or the DIMM slot itself.

5. Exit

Press Esc to stop the test and reboot. Remove the USB drive so the system boots normally.

Common Gotchas

One pass is not enough: Intermittent memory errors may not surface on the first pass. A system that passes one cycle can still fail on pass 3 or 4 as the RAM heats up. If the system has random stability issues, commit to a multi-hour run.

Secure Boot may block it: memtest86+ (the open-source version) is not Secure Boot signed. You may need to disable Secure Boot in BIOS to boot it. The commercial MemTest86 (no plus sign, from PassMark) offers a UEFI Secure Boot compatible version, but it is a different product.

memtest86+ vs. MemTest86: These are two different projects. memtest86+ (with the plus) is open-source GPLv2 from memtest.org. MemTest86 (no plus) is a commercial product from PassMark. Both work; the open-source version is what most IT techs carry.

ECC RAM may mask errors: On servers with ECC (Error-Correcting Code) memory, single-bit errors are silently corrected by the hardware. memtest86+ may show zero errors even if a stick is marginal. Check the BIOS event log or IPMI/BMC for corrected ECC error counts instead.

Does not test all RAM on some UEFI systems: On certain UEFI platforms, memtest86+ may not see all installed memory due to firmware memory maps. The commercial MemTest86 handles UEFI better. If your system reports less RAM than installed, try the legacy/CSM boot mode.