How to Perform a CPU Stress Test

The CPU, or Central Processing Unit, is responsible for all of the core math that your computer needs to perform in order to function. Although there are other processors in your computer, such as a graphics processing unit for visual representations, none of them have the general purpose flexibility of a CPU.

The last thing you want is for your CPU to fall over in the middle of something important. Whether it's an intense online gaming session or an important video rendering a client is waiting for, it's important to know that your CPU can handle the heat. This is where CPU stress tests come into play.

What is a CPU stress test?

A CPU stress test is a software program specifically designed to solve incredibly difficult problems for your CPU. It gives the CPU so many of these difficult math problems that it takes its full attention. The end result is a test of the maximum performance your CPU can deliver.

Most jobs in the real world, even those that consume 100% of your CPU, don't do it in this brutal and sustained way. You might be wondering why anyone would want to torture a bad CPU this way, but it's actually an important part of various aspects of computer building and maintenance.

Why should you stress test your CPU?

CPU stress tests are designed to push your CPU to its absolute limit and then see if it can handle such a heavy workload. CPUs generate heat when they work and need to stay below a certain temperature. If they get too hot, they can fail or even break permanently. When the CPU is dependent on something, or a sub-component of the CPU isn't working well, a stress test often reveals these problems in the form of crashes or a hanging computer.

In general, there are two real world scenarios where stress testing is common. The first is to test a computer build after everything has been assembled. Some boutique PC build companies have a "burn-in" period, during which the newly built computer is stressed non-stop for 24 hours. This is because any component in the computer that is failing will fail during the burn-in period.

The second reason for running a stress test is to check CPU overclocking. Overlocking deserves separate consideration and we have many articles on the subject. The short version is that an overclocked CPU has been set to a higher speed than the factory recommendation.

Any time you overclock your CPU, you should stress test it to make sure it's not overheating or somehow unstable. Stress tests are also useful without overclocking to test a new cooling system. Now the question is: which stress testing tools should you use?

The best CPU stress test tools

There are many applications that can help you ignite a fire under your CPU. Some are highly specialized and might be suitable if your computer is built for the type of CPU tasks they are designed for. However, for the vast majority of people, there are two general purpose apps that have stood the test of time.

Prime95

Prime95 is one of the hottest pieces of software you can run on a computer. The real purpose of Prime95 is to search for the largest prime number. That is, a number that can only be divided by one and itself. You can opt out of this research project when you run the program for the first time, and you should do so if you only use it for stress testing.

When the program starts in stress test mode, you have to make some decisions regarding the specific punishment.

The Blend option is best for general system testing, but as you can see some of the other options target specific components. So if you want to focus on RAM, for example, you can.

The number of threads will be filled in automatically, but should be equal to the number of cores in your system or double if your CPU has HyperThreading. Since our computer here has six cores with HyperThreading, we need 12 "workers", as they are called in the app. If you are happy with these settings, just press OK and you should see this.

Your computer is now running the CPU at full throttle, and you'll hear the fans speed up momentarily to deal with the extra heat. Once you've run the CPU stress test for the desired amount of time (and found no errors), you can press Check > Stop to give your poor CPU a break.

Heavy load

Unlike Prime95, HeavyLoad is not a repurposed scientific tool. Instead, it's an app built from the ground up for stress testing computers. One of the best things about this program is that it lets you tax your GPU and CPU at the same time. This is important if you want to check the stability of the entire system and plan to use the computer for tasks that use both types of processors.

You can toggle which components to stress using the handy toolbar buttons. If you're familiar with the default CPU+GPU option, just hit the play button and the torture begins.

HeavyLoad doesn't generate the lethal heat in a CPU like Prime95, but it does represent a more realistic maximum load. Prime95 is the gold standard for torture testing, but few real-world software will hit your CPU directly in the math with as much force. If it survives a HeavyLoad session, then it'll probably be fine for something like a video game.

core temp for temperature and system info

One of the main reasons for a stress test is to determine if your CPU is overheating or not. CoreTemp is a reputable tool that gives you important information about your hardware. For example, it shows you the real-time clock speed of your CPU as well as its technical data.

The main reason for using CoreTemp is of course the live temperature display. Each of your CPU cores gets its own individual temperature monitors. If you do a stress test, you'll see those temperatures go up. When your CPU reaches its maximum rated temperature, it will either throttle its speed to reduce heat or shut down the system for protection.

In CoreTemp, you can see all of this in real-time, which is invaluable if you want to know if unstable voltage, throttling, or excessive heat are responsible for poor CPU behavior.

Choosing the right stress testing methodology

It's easy to press the button that starts a stress test, but there's more to it than that! First of all, you have to let the CPU stress test run until the result is valid. In general, surviving a 24-hour test is a sure sign that the system doesn't fall over under load.

However, when you're overclocking and trying to find the sweet spot for frequency, voltage, and fan speed, there can't be 24 hours between each adjustment. In this case, you would run the stress test long enough for the CPU temperature to stabilize. This happens quickly with air cooling, but can take a while with liquid cooling. In this case, giving 15-30 minutes is a reasonable idea.

It's also worth noting that just because a system crashes under Prime95 doesn't mean it won't run video games with 100% reliability. If you're not overclocking and your system fails Prime95, it usually means upgrading your cooling setup or verifying that all cooling components are working properly.

Just remember the most important rule: the stress test is for your CPU, not for you!

By: How to Perform a CPU Stress Test