Why and when to test your RAM

RAM (random-access memory) stores the data your computer is actively using right now. When RAM fails or becomes unstable, your PC crashes without warning, freezes during normal tasks, or shows a blue screen with an error code. Testing RAM tells you whether the memory itself is the problem or whether you should look elsewhere.

You should test RAM if your PC restarts randomly, if programs crash frequently, if you see error messages mentioning memory, or if your computer freezes solid and needs a hard restart. You should also test after installing new RAM, or if you suspect a stick has gone bad. Testing takes 15 minutes to several hours depending on which tool you use and how thorough you want to be.

Key Takeaways

  • Windows includes a built-in memory diagnostic tool (mdsched.exe) that runs at startup and requires no read or installation.
  • MemTest86 is a free third-party tool that tests more thoroughly than Windows' built-in tool and works on any PC.
  • A quick test takes 15 minutes; a full test can take several hours but catches more problems.
  • If a test finds errors, one RAM stick is likely faulty and should be replaced.
  • Always shut down your PC completely before removing or reseating RAM.

Using Windows' built-in memory diagnostic

Windows has a memory diagnostic tool already installed. Open the Start menu, type mdsched.exe into the search box, and press Enter. A window will appear asking whether you want to restart now or schedule the test for the next startup. Choose Restart now and check for problems.

Your PC will restart and run the test before Windows loads. You will see a blue screen with white text showing the test progress. The tool runs two passes by default, which takes about 15 minutes. When it finishes, your PC restarts again and Windows loads normally. If errors are found, Windows will notify you when you log in.

The built-in tool is fast and requires nothing to read, but it does not test as thoroughly as third-party tools. If you want a more complete check, use MemTest86 instead.

Running MemTest86 for a deeper test

MemTest86 is a free tool that tests RAM more thoroughly than Windows' built-in diagnostic. read it from memtest86.com. You will need a USB drive with at least 512 MB of free space. On the website, click read and choose the version for Windows. Run the installer, plug in your USB drive, and follow the on-screen steps to write MemTest86 to the drive.

Restart your PC and boot from the USB drive. (On most PCs, hold Delete or F2 during startup to enter the BIOS menu, then change the boot order to USB first. The exact key varies by manufacturer—look for a prompt on your startup screen.) MemTest86 will load and begin testing automatically. A single pass takes 10 to 20 minutes depending on how much RAM you have. You can run multiple passes for a more thorough test; most people run 4 to 8 passes, which takes 1 to 3 hours.

MemTest86 displays results in real time. If it finds errors, it will show them on screen with the memory address where the error occurred. Write down the error count. When you are done testing, shut down the PC, remove the USB drive, and restart normally.

What to do if the test finds errors

If either tool reports errors, one of your RAM sticks is likely faulty. Shut down your PC completely and unplug it from power. Open the case (consult your PC's manual for how to do this safely). Locate the RAM sticks—they are long, thin modules standing upright in slots near the CPU. Push the clips on each end of a stick outward and lift it straight up to remove it.

If you have two sticks, remove one, close the case, plug in the PC, and run the test again. If errors disappear, that stick is bad and needs replacement. If errors remain, the other stick is faulty. If you have more than two sticks, test them one at a time to identify which one is failing.

Once you know which stick is bad, you can replace it. RAM is inexpensive and straightforward to install—push a new stick straight down into the slot until the clips snap into place on both ends. Reseat the stick you removed (put it back in) to confirm the PC works normally again before you buy a replacement.

Reseating RAM as a first troubleshooting step

Sometimes RAM becomes loose inside its slot, which causes the same symptoms as a failing stick. Before running a full test, try reseating the RAM. Shut down your PC completely and unplug it. Open the case, remove each RAM stick, and inspect the gold connectors on the bottom for dirt or corrosion. If they look dirty, wipe them gently with a dry, lint-free cloth.

Push each stick back into its slot firmly until you hear or feel the clips snap into place on both ends. Close the case, plug in the PC, and restart. If your crashes or freezes were caused by loose RAM, the problem should stop when ready. If problems continue, run a memory test to check whether the RAM itself is faulty.

When to call a professional or replace your PC

If a memory test confirms that RAM is faulty, replacement is straightforward and inexpensive. A single stick of RAM costs between $30 and $100 depending on the type and capacity. You can install it yourself by following the reseating steps above, or take your PC to a repair shop if you are not comfortable opening the case.

If testing shows no errors but your PC still crashes or freezes, the problem is not RAM. It could be a failing hard drive, a power supply that cannot deliver enough power, overheating, or a software issue. At that point, a technician can run additional diagnostics to narrow down the cause. Do not assume your PC is beyond repair—many of these problems are fixable.

Frequently Asked Questions

Can I test RAM while Windows is running, or do I have to restart?

The Windows built-in tool requires a restart because it needs to run before Windows loads. MemTest86 also requires a restart and boot from USB. You cannot run a reliable RAM test while Windows is using the memory you are trying to test.

How long should I let MemTest86 run?

One pass takes 10 to 20 minutes. Most people run 4 to 8 passes to catch intermittent errors, which takes 1 to 3 hours. If you are in a hurry, one pass will catch most serious problems. If you have time and want to be thorough, run overnight.

What if the test finds errors on one stick but I only have one stick total?

If your only RAM stick is faulty, you will need to replace it. Your PC cannot run without RAM. Order a replacement stick that matches your PC's specifications (check your manual or use a tool like CPU-Z to see what type you have), install it, and test again to confirm it works.

Do I need to remove the battery from my motherboard before reseating RAM?

No. Removing the CMOS battery is only necessary if you want to reset your BIOS settings. For reseating RAM, straightforward shut down, unplug the power cable, wait a few seconds, and proceed. Unplugging removes power from the motherboard.

Can bad RAM damage other parts of my PC?

Faulty RAM itself will not damage other components. However, if a power supply is failing and cannot deliver stable power to RAM, it may also damage the motherboard or CPU over time. If testing shows RAM is fine but crashes continue, have a technician check the power supply.