Why memory deserves its own procedure
Memory is one of the best used buys there is — it has no moving parts and no meaningful wear mechanism, so a stick that passes a test is genuinely as good as new. But faulty memory is also the great impersonator of PC faults. Random crashes, corrupted files, blue screens with a different cause each time, games that fail to launch, an install that mysteriously won't finish: all of those are classic bad-RAM symptoms, and all of them get blamed on the drive, the drivers, or the operating system first.
Testing it takes one evening of not using the computer, and it removes an entire category of doubt.
1. Check the sticks match the label
Before testing, confirm what you actually received. Read the part number printed on each module and compare it to the listing. Then boot and check what the system reports: generation (DDR4 vs DDR5), total capacity, the number of modules, and the rated speed. Mislabelled memory is a real problem in the used market — DDR5 sold as DDR4 and vice versa — and the part number is the authority, not the seller's description.
2. Run a proper memory test, overnight
Use a dedicated memory tester that runs before the operating system loads, rather than a utility inside Windows — a test running under Windows can't examine the memory Windows itself is occupying. Let it complete at least four full passes. This is why it's an overnight job.
The result is refreshingly binary: any errors mean bad memory. Not "a few is fine." One error in eight hours is a stick that will corrupt something eventually.
If you do get errors, test each stick individually, one at a time, in the same slot. That tells you whether you have one bad module or — occasionally — a bad motherboard slot, which is a different and more annoying problem.
3. Test at the speed you'll actually run
Memory ships at a conservative default speed and reaches its advertised rating only when you enable its speed profile in the BIOS (XMP on Intel platforms, EXPO on AMD). Test at the setting you intend to use. Memory that is stable at the default and unstable with the profile enabled isn't necessarily faulty — that combination of sticks, board and processor may simply not run that fast, which brings us to the most common non-fault of all.
The mixing problem, which looks exactly like bad RAM
Two 16GB sticks bought separately are not the same as a matched 32GB kit, even when the model numbers agree. Kits are tested as a set; separately-bought sticks can use different memory chips underneath the same part number. Mixed sticks very often work — and sometimes produce instability that every diagnostic blames on faulty memory when the real answer is "these two don't get along at this speed."
If you're mixing, the practical fallbacks are: run at the slower stick's rated speed, or relax the speed profile a step. If you're buying, a matched kit for the full capacity you want is worth a small premium over two singles precisely because it removes this variable.
Before you buy
- Match the generation to your motherboard. DDR4 and DDR5 are not interchangeable and don't physically fit each other's slots.
- Buy a kit, not a pile of singles, when you can.
- Photos of the actual labels, legible enough to read the part number.
- Check the going rate — memory prices move a lot, in both directions.
Every memory module we sell is run through a memory test, and the printed label is cross-checked against what the system actually reports — generation, capacity and speed — before it's listed. See memory in stock.