Few things in life beat the moment a PC you assembled yourself actually boots. The fans spin, the screen lights up, no smoke appears anywhere. Magnificent!

And then the doubt arrives. Is it fine, or fine for the next twenty minutes? Will the RAM hold at the speed printed on the box? Will the CPU still be at its boost clock in hour three of a render, or quietly throttling itself into a potato?

Stress testing is how you replace hoping with knowing. You take a component, load it far past anything normal software would ask of it, and watch what happens. Below are the tools worth using in 2026, in the order we would actually run them.

What Stress Testing Actually Proves

Let us be honest about this up front, because a great many guides are not.

A passed stress test proves your PC survived that load, for that duration, at that temperature. That is the whole claim. It is a useful claim! It is not a certificate of immortality.

What it is genuinely good at:

• Catching bad RAM, or RAM running at a speed it cannot handle
• Catching cooling that is inadequate, badly mounted, or slowly dying
• Catching a power supply that cannot deliver what the system demands under load
• Catching an overclock (or undervolt) that is less stable than you thought
• Catching a manufacturing defect inside the warranty window, which is the window that matters

What it is not good at:

• Proving there is no fault. Plenty of instability shows up once a week under a load no synthetic test resembles. A pass is evidence, not proof.
• Predicting gaming stability from a synthetic score. Games are a messy, bursty, mixed load. Prime95 is a very tidy one.
• Telling you exactly which part failed. Most tests report only that something went wrong. Some types of failures are easy to diagnose, many are not.

One honest warning: these programs deliberately create conditions your hardware would otherwise never see. Modern components throttle and shut down long before they cook themselves, but they are not infallible. Watch the temperatures, and do not walk away for eight hours on the first run.

Before You Torture Anything

Four minutes of preparation saves you an afternoon.

Install a monitor first. Skipping this is the most common mistake, because a stress test without a temperature readout tells you almost nothing. Get HWiNFO64, free for personal use, and run it in sensors-only mode alongside your test. It reports per-core effective clocks and package power draw, which is exactly what you need to tell throttling apart from instability.

Know your numbers first. Look up the maximum rated temperature for your specific CPU and GPU, because “70 degrees” has not been a sensible universal limit for about a decade. Modern chips are built to sit at 90 to 95 degrees under full load, and Ryzen in particular runs straight to 95C and stays there by design. That is the CPU doing its job, not the CPU dying.

Stop the computer going to sleep, because a test that ends because Windows dozed off at minute 30 has told you nothing. Close everything else, and take the overclock off before your first run. Establish that the hardware is sound at stock settings, then push it.

Testing the CPU

Start with OCCT. If you install one program from this article, install OCCT. It is free for personal use, actively developed, and does CPU, GPU, memory and power supply testing in one window with the monitoring built in and graphed. For most people, most of the time, OCCT is simply the correct answer. Run the CPU test on Auto for one hour. If it finds an error it stops, names the core, and shows you the temperature graph leading up to it. That last part is worth more than people realise.

Then use Prime95 when you want the worst case. Prime95 is thirty years old, still free, still updated, and still the most reliable way to learn whether your cooling is genuinely sufficient. The Torture Test menu is where everything happens:

• Smallest / Small FFTs stay inside the CPU cache. Maximum heat, maximum power, almost no memory involvement. This is your pure cooling test, and on an AVX-512 chip it pulls numbers you will never see in real software.
• Large FFTs brings the memory controller into it.
• Blend hits CPU and RAM together, and is the best general-purpose choice.

Run Small FFTs for an hour to test cooling, or Blend for six to twelve hours to validate an overclock you intend to trust. Prime95 checks its own maths as it goes, so a wrong answer means a hardware error, full stop. Any worker that stops is a fail.

Then add y-cruncher, which catches what the others miss. y-cruncher computes pi to absurd numbers of digits, and is unusual in hammering the CPU and the entire memory subsystem at the same time. That combination finds a class of instability that Prime95 and OCCT can both sail past, which is why it has quietly become the overclocking community’s favourite. Run it for one to two hours. A “Redundancy Check Failed” message is a fail.

And Cinebench, for a different question entirely. Cinebench 2026 is free and excellent, but it is a benchmark, not a stability test. Its job is to give you a number you can compare against other people running the same CPU. If your score lands 20% below where a stock chip of your model should be, you have learned something useful about your cooling or your power settings. Ten minutes. Do not use it to validate an overclock.

Testing the GPU

FurMark for the thermal worst case. FurMark 2 is free, supports OpenGL and Vulkan, and renders a spinning fur donut engineered to draw more power from your graphics card than any game ever will. It is the fastest way to find out whether your GPU cooling works, and also so unrealistic that drivers have historically detected it and throttled specifically to avoid it. Run it for 15 to 30 minutes, no longer. If artifacts appear, or the screen goes black, or the driver crashes, you have your answer well inside that window.

3DMark for the realistic load, with one caveat worth knowing before you download it. The 3DMark free demo includes Steel Nomad, Time Spy, and Fire Strike, which will tell you whether your card performs like other cards of its type. The looping stability test, the one that runs 20 passes and reports a frame rate variance percentage, is a paid feature. We still recommend 3DMark, because the free benchmarks are genuinely good at catching an underperforming card, but we are not going to pretend the stress test is free when it is not.

Superposition if you want a free GPU soak. Unigine Superposition is free and loops until you stop it. Thirty minutes is plenty. A current GPU will chew through this 2017 benchmark, but it loads the card far more honestly than the older Unigine tests do.

Testing the RAM

RAM is the part most likely to be the actual culprit, and the one people test last. Flip that around.

MemTest86 is still the definitive answer. MemTest86 v11.7 is free and boots from a USB stick outside Windows entirely, which is the whole point: it can test the memory an operating system would otherwise be sitting in. Nothing running inside Windows can claim that. Write it to a USB drive, boot from it, and let all four passes run. Four to eight hours depending on capacity, so this is the overnight one. Red text is a failure. A single error is a failure. There is no such thing as an acceptable number of memory errors.

One honest limitation: the free edition tells you that you have a memory error, but identifying which stick is at fault is a paid feature. The free workaround is older than the software. Pull all but one stick, test, repeat.

For a quicker check inside Windows, OCCT’s Memory test does a respectable job in an hour with no USB stick and no reboot. It is not a substitute for MemTest86 before you trust a system, but it is a fine way to sanity-check a new XMP or EXPO profile without losing a night.

A note on those profiles, since this is where most “my new PC is unstable” stories actually end: XMP and EXPO are an overclock. A factory-blessed, well-tested overclock, but an overclock. If your system is unstable and the RAM is running a profile, turn it off and test again before suspecting anything else.

Testing the Whole System

Individual components pass and the machine still falls over. This usually means the power supply, or heat soak: every part is within limits alone, but together they warm the case past what any single test revealed.

HeavyLoad is free, tiny, and loads the CPU, RAM, GPU, and disk simultaneously from a few checkboxes. It is not sophisticated and does not need to be. Run it for one to two hours and watch the temperatures climb higher than they did in any single-component test. That climb is the point.

OCCT’s Power test does the same job with better instrumentation and is the right choice if you suspect the PSU. Sudden reboots with no error message and no blue screen are the classic signature of a power supply that cannot deliver, as is a system that only crashes when the GPU and CPU peak together.

Testing Storage

Storage is the odd one out, and most guides get it wrong by treating it like the others. You cannot meaningfully stress test an SSD the way you stress test a CPU: writing enormous amounts of data to a drive to see whether it breaks mostly just consumes the drive’s finite write endurance, which is a strange way to look after something. The useful question here is not “can it survive punishment” but “is it healthy and performing correctly”.

So: run CrystalDiskInfo first. It is free, open source, and reads the SMART data your drive has been quietly keeping about itself the entire time. Anything other than “Good” in blue needs investigating today. Reallocated sectors, pending sectors and a plummeting remaining-life percentage are the drive telling you what is coming. Believe it.

Then run CrystalDiskMark, also free, for five minutes and compare the sequential and random numbers against the drive’s advertised speeds. An NVMe drive delivering SATA speeds is usually in the wrong slot, thermally throttling, or sharing bandwidth with your graphics card. All three are fixable in an afternoon, and that is about as far as “stress testing” storage sensibly goes.

The Short Version, in Table Form

What “Passing” Actually Means

A pass is three things together, and the first one is the one people forget:

1. The test ran the full duration without stopping. Not “it looked fine when I checked”.
2. Zero errors. Not few. Zero. Every tool here is built so that correct hardware produces correct answers, so any wrong answer is a hardware problem.
3. Temperatures stayed in spec and clocks stayed up. A machine that finishes an hour of Prime95 by dropping to 2.1GHz has technically passed and practically failed. This is why you run the monitor.

If all three hold, your hardware is sound under that load. Go and use it.

When It Fails

Right. Something went red. Do not order parts yet, because the cheap causes are also the common ones. Work through these in order:

1. Reset the BIOS to defaults. Turn off XMP or EXPO, remove every overclock and undervolt, and test again. An enormous share of “faulty hardware” is a memory profile the kit cannot quite hold.
2. Reseat things. Pull the RAM out and push it back in until it clicks. Same with the graphics card. Check the CPU cooler is actually tight, because a cooler mounted a quarter-turn loose produces exactly the temperature curve of a dying chip.
3. Update the BIOS and the GPU drivers. Memory compatibility improves substantially over a motherboard’s life, and this costs nothing but twenty minutes.
4. Test one part at a time. One stick of RAM, then the other. Onboard graphics instead of the card, if you have them. Tedious, and also the only way to identify the culprit rather than guess at it.
5. Check the temperatures again, honestly. If the CPU hits its limit within 60 seconds of load starting, the problem is the cooler mounting or the thermal paste, not the CPU.

If you have done all five and a component still fails, you have found genuine faulty hardware, which is a far better outcome than not knowing. Check the warranty first, because a part that fails a stress test is a part you can demonstrate is broken, and that is a strong position for a return. If it is out of warranty and needs replacing, our main PC parts list is organised by budget and updated constantly, so you can find the sensible replacement at your price point without a fortnight of research.

The Ones We Retired

This article recommended a different set of tools for years, and four have aged out. Better to say why than to quietly delete them:

IntelBurnTest has not been updated since 2012, and wraps a version of Intel’s LINPACK that predates AVX2, AVX-512, and every Ryzen chip ever made. OCCT’s Linpack test does the same job on hardware that exists.

Super PI is single-threaded, so on a modern CPU it loads roughly one sixteenth of the chip. y-cruncher does the same mathematics across all the cores and checks its own results.

Unigine Valley still downloads perfectly well, so this is not an obituary. It is simply a 2013 benchmark, and a current graphics card runs it at hundreds of frames per second without breathing hard. A test your GPU finds easy is not a stress test.

HWMonitor was not wrong. It has just been comprehensively outclassed by HWiNFO64.

Go forth and torture your hardware responsibly. Have we missed a tool you swear by? Let us know in the comments, and may all your tests be boring.

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