Prime test 95: How To Stress Test Your CPU + Best Prime95 Settings

How To Stress Test Your CPU + Best Prime95 Settings

If you have not done any CPU Stress testing or worked with Prime95 before, then you might not be aware of the best Prime95 settings. These perfect CPU stress-testing settings will turn up the heat on your overclocks like no other tool – The only exception to that is OCCT.

Prime95 has been around since the dawn of time and used by overclockers and PC enthusiasts to stability test CPU overclock by place a heavy load on the CPU as well as the rest of the computer hardware. This maximises heat output, voltage drain and overall stress on your computer’s components.

When you just need more stress for your CPU

Back in the day, unlocked multipliers on CPUs were reserved for the elite who had extremely deep pockets – if you had the balls, maybe you unlocked your Athlon XP 2500+. As a result, we needed software capable of simultaneously putting a huge amount of stress on both the processor and ram because there was a lot of front-side bus overclocking.

Today, overclocking has evolved; most processors have unlocked multipliers, and if they don’t, there is always an accessible modal.

Regardless of the state of overclocking, Prime95 remains one of the best overclocking tools in our arsenal here at PerformancePSU to really burn our components and test the stability of our big overclocks.

Table of Contents

If you are not a small talk type of person, you can skip straight to the best prime95 settings section.

What is Prime95?

Prime95 Stability Test Software

Primarily a CPU stress testing tool or CPU stability test as it’s sometimes also called, Prime95 places an extreme amount of pressure on your entire computer system, including your power supply, memory, processor and motherboard, using a set of predefined tests.

Prime95 works by requesting that your computer’s hardware calculate prime numbers in rapid succession and will do this until;

  1. It finds a unique prime number at which point you will be notified by a sound.
  2. You stop the test (our ideal scenario)
  3. Your hardware fails and the test fails due to a miscalculation (our worst-case scenario)

Common Questions

Why Should I Stress Test My CPU?

When you overclock your CPU you place an additional load on all of your pc components this includes your motherboard, ram, graphics card and power supply. A system is not stable just because you can boot into Windows and browse Facebook. You need to verify the stability of your computer by putting it through a series of tests designed to push your system to its limits.

These stress tests or as they are otherwise known in the overclocking community, stability tests, will ensure your computer doesn’t randomly crash while under intensive processing load resulting in your potentially losing that clutch game or pivotal document you spent all night writing.

Does Prime95 test my Graphics Card (GPU)?

Prime95 stability tests your processor, ram, power supply and motherboard. It cannot stability test your graphics cards (GPU) because it does not have the available instructions to make use of them.

How long should I run Prime95 for?

PerformancePSU advises to run Prime95 for 12 – 24 hours to make sure your system is 100% stable. Normally though, unstable overclocks will show up pretty fast, normally within around the 30-60 minute mark which is where it can be handy to run a simple blend test.

What are the best Prime95 Settings?

For most people, the blend test is the perfect way to tell if their computers overclock is stable. However, if you want to push your components further and conduct a real stability test, custom Prime95 settings are your best bet. If your overclocking PC can complete 24 hours at these settings, your overclock will be rock-solid.

Custom Prime95 Settings for Maximum Load

To stress test your CPU with custom Prime95 settings, follow these steps:

  1. You will need to download Prime95 if you don’t already have it.
  2. Start a New Torture Test
  3. Select Custom Blend
  4. Set the number of threads to the number of cores you have (double that for virtual cores)
  5. Press Ctrl + Alt + Delete to check the available ram in start task manager under the Performance tab
  6. Calculate 90% of your total system memory using the following calculation: amount_of_memory_in_mb * .9
  7. In the box that reads “Memory to use in MB” insert the sum of step 3
  8. Click Start

Note: Your entire system will slow down during the custom stability test, so don’t expect to use your computer for other tasks while the test is running.

In conclusion, Prime95 is an essential tool for PC enthusiasts and overclockers to stability test their CPU overclocks. With the best Prime95 settings, you can ensure that your overclocked system is stable and reliable. Don’t hesitate to stress test your CPU for 12-24 hours to guarantee maximum stability and avoid any potential crashes.

Download Prime95 — MajorGeeks



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MajorGeeks.Com » System Tools » Processor » Prime95 30.9 Build 3 Beta / 30.8 Build 17 / 30.8 Build 15 » Download Now

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Prime95 for Windows and Linux is a small and easy-to-use freeware application that allows you to find Mersenne Prime numbers designed for overclockers.

Mersenne numbers can be proved composite (not prime) by either finding a factor or running a Lucas-Lehmer primality test.

Prime numbers have long fascinated amateur and professional mathematicians. An integer greater than one is called a prime number if its only divisors are one and themselves. The first prime numbers are 2, 3, 5, 7, 11, etc. For example, the number 10 is not prime because it is divisible by 2 and 5.

A Mersenne prime is a prime of the form 2P-1. The first Mersenne primes are 3, 7, 31, 127, etc. There are only 40 known Mersenne primes.

There are two ways to use this program. The automatic way uses a central server, which we call the PrimeNet server, to get work to do and report your results. Anyone with Internet access, including AOL, CompuServe, and dial-up ISP users, should use this method. You do not need a permanent connection to the Internet.

The second method is the manual method. It requires a little more work and monitoring. It is recommended for computers with no Internet access or some firewall problem that prevents the automatic method from working.

Version History for Prime95:

Screenshot for Prime95

« HiSuite by Huawei Android Smart Device Manager · Prime95 30.9 Build 3 Beta / 30.8 Build 17 / 30.8 Build 15
· CloseTheDoor 0.2.2 »

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How and at what stage should testing be completed?

The beginning is half the battle. This rule applies to almost any field of activity, and even to software testing.

Often at the beginning of a project, testers exude enthusiasm by writing documentation (test strategy, test plan, or test cases).

But in the future, difficulties often arise. At the end of the first round of testing, testers usually find a bunch of bugs, and then come to the second stage somewhat relaxed. There is a so-called. the human factor and the general human tendency when it becomes boring to perform repeated operations.

In these situations, many people feel like they are doing monotonous work, and as a result, they lose interest in continuing to test already familiar software. And during the third, approximately, round, the question inexorably hangs over the tester: “When do you need to stop testing?”

Every tester at least once asked this question, the extended version of which would look like this:


  • “When, at what stage and how to stop testing?”
    • Is that enough already?
    • Is that enough?
  • Termination or exit criteria
  • What does the exit criterion include?
  • Testing can be completed when:
  • Test coverage:
  • Deadlines:
  • Test documentation:
  • Budget:
  • Finally, please answer a few questions

“When, at what stage and how stop testing?

Many testers believe that there are no special conditions that indicate that testing should be completed. But to answer this question, you will have to analyze the test activity from beginning to end.

Suppose the task is to test a new project.

Initial actions:

  • The test team receives the requirements.
  • This is followed by planning and development.
  • Prepare and review test documentation for .

Testing Round #1)

The test team begins testing as soon as they are handed the newly created software product.

During the testing phase, testers run various scenarios in an attempt to crack the software and find defects. (Because the application is new and is being evaluated for the first time, the defect rate will be relatively high.)

Developers fix defects and return development to testers for retesting.

Testers check for defects, then move on to regression testing.

Once major bugs are fixed and the software is stable, the development team releases the next version.

Testing round #2)

Testers begin the second round of testing and repeat what was done during the first round.

During this process, some more defects are usually found.

Defects are fixed by the developers and the application is resubmitted for review.

Testers conduct retests and regression testing of parts of the development that have not changed.

This can be continued indefinitely. Round 3, 4, 5…until the software is completely bug free.

Graphically, this process can be depicted as follows:

But is it theoretically possible to find absolutely all defects? This is a million dollar question, but let’s try to answer it.

Most of the applications are complex, that’s why the scope of their testing is quite large. Not that it is completely impossible to detect absolutely all defects, but this will take eternity.

Even after most software bugs are found, no one can say for sure that the application has become flawless.

Moreover, such a task is not worth it. The purpose of software testing is to make sure that it is functional and works as planned. This is achieved through hacking attempts or looking for deviations from the expected behavior.

Applications can have an infinite number of defects, and it is impractical to test software until they are completely fixed. You never know which bug will be the last.

And if «stop testing when defects are completely fixed» is no longer a criterion, then what should be the starting point?

Let’s try to figure out which factors should be considered the most important?

The decision to stop testing usually depends on the time (available), budget, and required duration of testing.

Most often, the decision to end a test is made when time/budget runs out, or when all test cases have been completed. But this is a compromise solution, which can be at the expense of quality.


Test script:

Suppose you need to test a software module, a certain budget is allocated for this work. Time: 1 month. Total number of test scenarios: 200 But testing stopped for 3 days. You cannot check other scripts until the discovered bug is fixed. After wasting time, you get back to work.

By the end of the week, 20 scripts were checked and several more dangerous bugs were found.

Week 2 : You start testing, carefully looking for defects. During the second week, find several bugs of the 1st, 2nd and 3rd level of criticality. During this time, 70 scenarios were tested.

Week 3 : By the beginning of the third week, all high priority defects were fixed, but now a recheck of previously discovered bugs is now added to the execution of current scripts. In the third week, you covered 120 scenarios and found a few more bugs. Now it remains to look for only third-order defects.

Week 4 : Defects and the 80 remaining scenarios must be rechecked by the start of the fourth week. By the end of the week, you’ve tested 180 scenarios; all high priority defects have been fixed and retested.

Data on the test performed are placed in the table:

Weeks #1-4
Work Results after a week
Week #1
  • First day — Show Stopper defect found.
  • Testing stopped before a dangerous defect was fixed.
  • The defect was fixed on the fourth day.
  • Testing continued.
  • Critical errors detected.
  • 20 scenarios tested.
Week #2
  • Special attention to defects.
  • Run remaining test scripts.
  • Re-testing for defects.
  • Several more level 1, 2 and 3 defects have been found.
  • Total number of tests completed 70.
Week #3
  • Rechecking and searching for major defects.
  • Run remaining scripts.
  • It remains to find defects of the third level of criticality.
  • Multiple level 1, 2 and 3 defects found.
  • 120 scenarios tested.
Week #4
  • Retesting for high and medium level defects.
  • Execution of test scenarios.
  • Multiple level 3 defects found.
  • Total number of scenarios tested 180.

Is that enough already?

Test time has expired. You have found and eliminated a number of first-level defects. If we stop there, can the developed software be considered reliable? Not really, for some reason:

  • Not all scripts have been tested.
  • Several potentially dangerous defects were never tested.
  • All tested scenarios were only tested once.
  • The software still has defects.
  • Regression testing was not performed.

Scenario #2)

Week 1 : You find a Level 1 defect on the first day of testing. And testing is delayed by 3 days. After losing three days, you get back to work.

By the end of the week, 20 scenarios were checked, and several more dangerous defects were found.

The results of the first week are the same as example #1.

Week 2 : During the second week you find several bugs of the 1st, 2nd and 3rd level of criticality. But now the task is to cover as many scenarios as possible. As a result, 120 scenarios by the end of the week.

Week 3 : By the beginning of the third week, all priority defects have been fixed, and now, in addition to the current scenarios, it is necessary to recheck previously detected defects. In the third week, you covered 200 scenarios and found a number of bugs.

You can now only report second and third level defects.

Test data:

Weeks #1-3 Work Results after a week
Week #1
  • First day — Show Stopper defect found.
  • Testing stopped before a dangerous defect was fixed.
  • The defect was fixed on the fourth day.
  • Testing continued until the end of the first week.
  • Critical errors detected.
  • 20 scenarios tested.
Week #2
  • The main focus on the number of scenarios, in order to make up for lost time.
  • Retesting of fixed defects.
  • Several more level 1, 2 and 3 defects have been found.
  • Total number of tests completed 70.
Week #3
  • Rechecking and searching for major defects.
  • Run remaining scripts.
  • It remains to find defects of the third level.
  • Multiple level 1, 2 and 3 defects found.
  • All scripts have been checked.

Is that enough?

You have fully covered all test scenarios, found a few more defects. If we stop there, can the software be considered reliable?

Not quite:

  • All scripts were only tested once.
  • The software still has defects.
  • Regression testing was not performed.

As you can see, both scenarios do not guarantee quality. It is best to try to find a middle ground in such a situation, to use an approach that would take into account all the best features from the first and second scenarios. To do this, you need to define a number of criteria.

Completion or exit criteria

The exit criteria determines how much testing should be considered sufficient. It is determined at the end of the testing cycle and included in the plan. This is a set of conditions or activities that must be met in order for the test to be called complete.

What does the exit criterion include?

Ideally, this is a combination of several factors that are unique to all projects. It all depends on the requirements of a particular project. Therefore, during planning, it is more expedient to calculate as many parameters as possible.

Below are some things to consider during functional or system testing. You can choose a combination or use all of these factors to determine when to complete testing.

Testing can be completed when:

  • All 100% requirements are met.
  • Defects found/expected number of defects found.
  • All Show Stopper or Blocker bugs have been fixed, none of the critical bugs have an «open» status.
  • All high priority defects identified and fixed.
  • Defect Rate (defect formation rate) is below the set allowable level.
  • A very small number of medium-severity defects have been “opened”, they have been analyzed.
  • The number of “open” medium-level defects that do not affect the use of the system is very small.
  • All defects with a high priority level have been closed and the corresponding fallback scenarios have been successfully run.

Test coverage:

  • Test coverage should be at 95%.
  • The Pass Rate of the text case must also be 95%. The following formula is used to calculate this percentage:

(Total number of successful text cases / total number of test cases) * 100.

  • All critical test cases were successful
  • 5% of test cases can fail, but this applies to low priority cases.
  • Full functionality coverage achieved.
  • All major functional defects have been successfully fixed.


The testing period has expired.

Test documentation:

All test documentation to be submitted (eg test report) prepared, reviewed and submitted.


  • The budget allocated for testing has been fully spent.
  • Go / No Go meetings have been held, the decision to release the product has been made.

Finally, please answer a few questions

If the majority of the answers are yes, this means that you can complete the test.

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