Testing memory before you resell a machine

Why every machine gets tested

A memory fault is often hard to spot. A machine with a failing module may boot, install Windows and pass a quick look, then crash under load, corrupt files or fail an update weeks later, in the buyer's hands. Those returns cost far more than the bench time a proper test takes, and most of them are avoidable.

Test every machine whose memory you have touched, and every machine you resell, whether or not you fitted anything. Memory that has been through a lease, a collection and a warehouse has had plenty of chances to work loose in its slot or be damaged, and a module that worked in the original owner's office is no proof that it works now.

First check: does it see all of it

Start with the simplest question: does the machine report the memory it should? Compare the total shown in the BIOS or UEFI setup screen, or in Windows, with what the spreadsheet or your own fitting record says. A 16GB machine reporting 8GB has a module that is missing, unseated or failed, or a slot that is not working.

In Windows, Task Manager's Performance tab shows the total, the speed, the number of slots used and the form factor. Check that a machine with two modules shows two slots in use, and that the speed is one the platform supports. A DDR4-3200 module running at 2666 in an older machine is normal; a machine that should have two modules showing only one slot in use needs a closer look before anything else.

The maker's own diagnostics

Most business machines carry hardware diagnostics in their firmware, which run without an operating system and include a memory test. On Dell machines, the boot menu, reached with F12 at power-on, offers the built-in diagnostics. On HP business machines, pressing Esc at power-on and then F2 opens HP PC Hardware Diagnostics. Most recent Lenovo ThinkPads list a diagnostics option in the startup interrupt menu, reached by pressing Enter at power-on.

The quick tests take a few minutes and catch obvious failures. Most tools also offer an extended memory test, which takes considerably longer and finds more. A quick test is a sensible screen for every unit as it arrives; anything that has had memory fitted, or anything going out at a premium, deserves the extended test or a full pass with a dedicated tool.

Windows also includes Windows Memory Diagnostic, started by typing mdsched into the Start menu. It restarts the machine and tests before Windows loads. Its standard test is basic, but its extended option is a reasonable fallback on a machine without firmware diagnostics.

A full pass with MemTest86 or Memtest86+

For a thorough test, boot the machine from a USB stick running MemTest86, from PassMark, or the open-source Memtest86+. Both test the memory directly, without Windows in the way, and current versions of both support modern UEFI machines and DDR5. Make a handful of sticks and you can test a row of machines at once.

Let the test complete at least one full pass, through every test in its sequence. MemTest86 runs four passes by default, which is a sound standard for machines you are selling. Time grows with capacity, so plan bench time by the gigabyte rather than by the machine: a 32GB workstation takes far longer than an 8GB ultrabook. Running tests overnight, in rows, is the usual way through a large lot without holding up the day's work.

Keep laptops on mains power with the lid open during long tests. A battery running flat halfway through a pass wastes the time already spent, and a laptop runs cooler with its lid up.

When a test fails: module, slot or board

Any error is a failure. Memory either holds data correctly or it does not, and a single error in a long pass is enough to cause the crashes buyers return machines for. Do not pass a machine because the error count was low.

Then find where the fault lives. With two modules, test each on its own in the same slot. If one fails and the other passes, the module is at fault: replace it, then test the pair again. If both pass on their own, move a known-good module through each slot in turn. A fault that follows a particular slot points to the motherboard, not the memory.

Before blaming either, reseat the modules and look at the contacts and the slot for dirt or damage; a module that worked loose in transit can fail a test and pass once it is reseated. Where memory is soldered to the motherboard, a failure is a board-level fault, and the machine becomes a repair project or a parts unit, graded and described as such.

Record the result

Write down what you tested, with which tool, how many passes and the result, against each machine's serial number. It takes seconds per unit and pays back the first time a buyer reports a problem: you can show the machine passed before it left, and you can see whether one model or one batch of modules is failing more often than it should.

Trade buyers often ask how stock was tested. A spreadsheet column that reads memory tested, four passes, no errors, is a stronger answer than tested and working, and once testing is part of the routine it costs nothing extra to give.