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How Long to Run Prime95? [Here’s the Answer] 2022

The universe is based on stability. So how do you think that the computers would be wary of the feature!

Similarly, the pieces of software embedded in the system need to be stable to execute the tasks within the given timeframe. And this is where the role of stability testing comes.

The basic purpose of the process is to ensure that the software executes all of the functions within the given scope.

In addition, the test environment also shows the metrics like normal load, overclocking features (refer to how to reset overclock), errors or bugs if any, and many more.  

And when it comes to knowing the freeware applications for stability testing, the QA engineers recommend Prime95.

Simple interface, accurate results, zero crashing are all features of the amazing application, and hence becomes a favorite amongst the people of overclocking community. Interested to learn more?

Read on to know about how long should you run Prime95.  


Prime95 CPU Stability Tester: The Basics

Developed on 3rd January 1996, Prime95 has been one of the favored tools amongst the developers’ community, especially the overclocking ones. The upcoming section would give you a briefing on it. 

What Is Prime95?

Written by George Woltman, Prime95 is a freeware application that uses the GIMPS mechanism. GIMPS is a distributed computing network used for finding the Mersenne Prime numbers, and these numbers indicate the overall stability of the system.

prime 95 software

Now, if you want to go by the Mathematics behind it, then the two primary algorithms used are LL and Fermat Primality Test.  

How Does Prime95 Tests CPU?

The thumb rule states that the operations run by Prime95 exert load on the various sub-systems of the computer because the parameters selected under those are very stringent.

As a result, the developers gain a chance to assess the critical components, like CPU, RAM, FPU, power delivery, and many more. 

Prime95 stress test takes the CPU to the maximum limit, runs indefinitely, and finally terminates after witnessing an error. It gets displayed on the system, and can also highlight the potential error or instability. The unit for measuring the failure is called FPU, abbreviated as Floating Point Unit.  

FPUs perform plenty of complex calculations, and one of those include FFT (Fast Fourier Transform). It is a complex algorithm to find the square of large numbers, and completes the same through the given configurations:

  • Small FFTs
  • In-place large FFTs
  • Blend
  • The custom setting defines the min and max size, and time of the run. 

What Results Can You Get and What Do They Mean?

Different types of tests can be run on Prime95- CPU stability test, Torture test, Just Stress Testing being the popular ones. They differ in terms of the settings given on Small FFTs, In-place large FFTs, Blend, and Custom settings. 

prime95 stress test

The basic parameter of measuring the performance is defined in terms of time, where the lower value means faster and better performance of the system. However, another concern to which you need to pay attention is the errors during the run.

In a non-overclocked situation, you may receive hardware errors due to overheating the CPU, improper attachment of the heat sink, power supply incompatibility, DIMMs not meeting the spec, and many more. Similarly, in the overclocked situation, errors pop up due to lesser core voltage, insufficient latency timings, higher Front Bus speed, and others. 

Keep an eye on the symptoms to find the exact cause for Prime95 not running.

How Long to Run Prime95?

The answer to the question ‘How long to run Prime95 in 2022?’ varies based on the type of test that you run on Prime95. For example, if you are running a stress test on an overclocked system, it should be allowed to execute for 12-24 hours before concluding without any errors in the program.

There may be some errors after some hours due to a little phase of instability, but they need not be that serious. You need to refer to the error code to deep dive into this.

Similarly, for the Torture test, the ideal time is 5-30 minutes for judging the general stability. If it passes in the first run, keeps increasing the multiplier of FSB, reboot, and then re-run the program until errors pop up. Post that, work on error resolution and run the Torture test for 12 hours. 

running a torture test with prime95

On average, when you go for Torture Test Level 10, the system has to run for at least 12 hours and after that, you may gain visibility on the overall stability. 

How Long Does Prime95 Blend Test Take?

Now, let’s focus on the basics of the Blend test. As goes by the name, it blends or mixes the test cases of Small and Large FFTs. The smaller ones will play more with the CPU, whereas the larger ones will keep using the memory as they would not be enough for the cache. In simpler words, you would be getting to test both CPU and RAM. 

On average, the Blend Test should run for 3-24 hours to find the perfect stability. It is because the entirety of CPU and RAM is used in the process, and any failure in the test will give a clear indication of bad component(s). Particularly, it will help you to decide if your RAM is bad or not.

The reasons for such a long time include the following:

  • It utilizes the maximum memory value of the CPU to stress it and keep busy at times. If things move to the Virtual Memory, then the results would not be correct as the hard disk would come in between. 
  • Sometimes, the values in the settings are not put properly and may show under-utilization in Task Manager. To avoid that, you may need to re-iterate the entire process unless you find the set that works properly. 

If you are running the test on an overclocked system, then the duration may last 24 hours. So, it also depends upon the system configurations while testing. 

How Long Does Prime95 Benchmark Take?

Prime95 Benchmark usually refers to the thorough analysis done on the system to determine different cases- stability of the computer, the possibility of overclocking, and the extent to which overclocking is allowed. Now, there can be two situations arising here – the system terminating the stress, or the user doing so voluntarily.

Prime 95 benchmark

In the former case, the system runs until an error is reported, and then the codes show the degree of instability in the system.

However, in the latter, the user may decide to go away with the test once he or she thinks that it has run for sufficient time. In either of the cases, the time stays the same as mentioned above. 

If you are running the Torture Test in Prime95, then the duration would be higher than the normal scenario. It is to ensure that the system stays full-proof, and the performance graphs stay in line with the manufacturer’s requirements. 

If you are going for the Blend Test, the benchmarking time is decided based on the Prime95 time to run each FFT size.

Tips to Use Prime95 Effectively

Prime95 is not an easy nut to crack, especially for those who are new to the overclocking community. Therefore, you must know the tips to use them effectively.

prime 95 software help option
When in doubt, you can always use the HELP option

The following are some handy ones:

  • Never run Prime95 in parallel to any other stress testing tool. It would create unnecessary load on the CPU and other components and may require you to keep the system on for longer hours. Be assured, the results from Prime95 are accurate and indicative of the overall system health.
  • Be fully informed on the nitty-gritty of Prime95 before using it. Refer the useful journals or forums to understand the concerns and general mistakes often made by the testing community.
  • If you have an Intel chip that uses Hyperthreading, then run two instances of Prime95. It is because the first cannot determine cent percent results on instability. So, you may need to run the program from another folder. There are ways to automate the same and ensure that the second instance runs immediately after the first one is terminated. 
  • Set the parameters very carefully. For example, in the Stress test, if you run the program on memory exceeding the requirements of the CPU, then the system would tend to use the virtual memory, and it involves running the hard disk. As a result, the readings would not be correct, and you would never be able to conclude on the instability in the CPU. 
  • Keep an eye on the CPU temperature also, as it can be indicative that you are overstressing the system, and the cooling system is inefficient in handling such loads. 

The moral of the story is that you should use Prime95 efficiently, in a way that it diagnoses the stability and does not hamper the system further. 

Which Prime95 Test to Run for Stress Testing?

There is a clear option for Stress Testing, under which you can run the program successfully. Once you download the zip file of Prime95, unlock it, complete the installation, and select the option- Just Stress Testing, to initiate the process.

You can also test a specific exponent

Select the FFT size and the test would commence on the input conditions. Here, the run happens based on each logical thread in the CPU and will keep updating the same based on real-time information.

If the system encounters an error, the other worker threads would stop and the code would be displayed on the screen.

To further deep dive into the error, just open the file and study the same. If there is no error, then the test cases continue. 

Just remember that there would be two results to stress testing- full pass and the computer would not display any error code, otherwise some code and the same needs to be diagnosed.

Keep the guidebook handy to understand the root causes, and work accordingly for resolving the same. 

What to Do If Prime95 Is Not Running?

Now, there can be ways in which Prime95 would not be functioning as per the intent. Some of the symptoms for it include the following:

  • The temperature of the CPU exceeding the given limits even in the first few hours of the running of the program.
  • The input parameters consume memory greater than the available space within the CPU, and hence hard disk also comes under load along with CPU and RAM (which should never be the case).
  • An improper power supply that is not able to handle the CPU is being pushed to the greater limits. 

In all of the cases, the best solution is to reset the parameters and ensure that the above constraints are not violated. Despite that, if you still find issues with Prime95, then the only solution is to find its alternative. Some of the popular options include the following:

  • OCCT, known for the fastest lead time in detecting hardware and stability issues.
  • HeavyLoad, known for good customization features to meet the user test requirements.
  • System Stability Tester, that can help in determining the stability by calculating the maximum possible digits in Pi.
  • LinX is a favored tool for CPU performance and stability.  
  • Stress My PC, which is known for ergo computer stress to pushes the system to the maximum limit and lets it run till the point the battery allows. 

Keep your options open, and ensure that you make an informed decision before switching out of Prime95. Refer to one of such similar article- ganged vs unganged. 

Frequently Asked Questions

Does Prime95 stop automatically?

Prime95 is a diagnostic tool, and it would keep running unless it finds some deviation against the known or set results. Then, it terminates the program and displays the code to the viewers for their identification. In an erstwhile case, if the user thinks that the test has been running long, then he or she may choose to terminate the program. 

Should I use Prime95?

Prime95 is a well-known freeware application that has an excellent algorithm for finding the root causes of multiple hardware issues. Also, there are many forums made by overclocking experts that guide the newbies on the dos and dont’s and explain the multiple error codes. So, there is no harm in trying.  

How should I run Prime95?

Once you launch Prime95, you will be given the option to run Stress or Torture Tests. Go for the one that meets your requirements, and then set the four parameters- Small FFTs, In-place Large FFTs, Blend, and Custom option. Be sure that you give the right set of input values, and your system would run accordingly. Keep referring to important blogs to decipher your concerns. 

Which version of Prime95 should you use?

There are two versions of Prime95- the older one that does not have an AVX instruction set, and the newer one that has. If you go by the latter, then it would produce a good thermal load and hence it is highly recommended to not go for it unless your system can handle it.  

Is it safe to run Prime95 overnight?

It depends upon the input parameters given by you. If they are within the system requirements and do not overheat it, then it is fairly safe to keep running it overnight. If your CPU temperature exceeds, then it is advisable to terminate the program and re-run it during the active hours of the day.  

Final Words 

On an ending note, it can be concluded by saying that Prime95 is an efficient tool in diagnosing the multiple hardware units that affect the overall performance of your system. Based on the severity of the test, the duration would differ. But, the developers’ community is impressed by the results it shows. There would hardly be any difference or inconsistency.

In addition, you would find multiple guidelines online for the parameters to set, dos, and don’ts in the system, and deciphering the error codes displayed. Keep an eye on those, and also post your concerns for a quick resolution. 

Keep reading our website for more of such topics, like ‘Does overclocking GPU make a difference?’ and many more.