MemTest verifies the reliability of RAM. A correctly functioning computer should be able to store data in memory with 100% accuracy for months. A computer that fails these tests, perhaps because of old hardware, damaged hardware, or poorly configured hardware, will be less stable and crash more often. Even worse, it will become even less stable over time as corrupted data is written to hard disk.
By using MemTest you can ensure that your computer's RAM is functioning correctly. This is a good thing to check whenever you buy a new computer, install new RAM, or change the configuration of your machine (for instance, to overclock it). If you are the sort of user who likes to push the performance of your machine to the edge, relying upon whether your machine will boot after your new BIOS tweaks is a poor way to determine the safety of your new settings. Use MemTest as a true test of stability.
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How much RAM to test: Only test the amount of RAM that is unused, rather than the total amount of RAM in your system - otherwise your computer will spend 99% of the test reading and writing to your hard drive, rather than testing RAM. By default MemTest will check all RAM that is not in use by other applications. If you want more control, you can use the Windows Task Manager to determine how much RAM is free. As a rule of thumb, Win9X uses about 32MB of RAM when nothing is open, and Windows2000/XP uses about 64MB. Vista/7/8/10 use quite a bit more, depending on what features you have enabled. Even though you cannot directly check used RAM, Windows dynamically moves the location of most of its subsystems, so most of your RAM will be checked eventually.
No Windows program can directly check the RAM used by the OS; this is a fundamental limitation of using a modern OS. If you need to check every byte, consider purchasing MemTest Deluxe, which boots off of CD for unfettered access to RAM.
How long to test: Executive summary: 100% coverage represents a very thorough testing your memory, and will catch all but the most intermittent problems. To catch those much more rare intermittent errors run to 400%.
Empirically we have found that the vast majority of errors are found in just a few minutes. 60% of bad RAM is detected after just 10% MemTest coverage. Running the test 10 times longer (100% coverage) raises the bad RAM detection rate to 95%. The remaining 5% are intermittent errors. Unfortunately, there's no way to speed up detection of intermittent errors - you have to wait for them to happen. The same pattern may be stored accurately the first 1000 times it is written, only to fail on the 1001th write. We have found that testing to 400% coverage will catch almost all intermittent errors, but rather than trying to hit that number exactly, we recommend testing overnight. Your computer is not doing anything else at night anyway. Or, you can run MemTest Pro while you use your computer for other tasks, which can also help identify memory errors which only show up while the computer is under normal load.
MemTest will report any errors that it finds as soon as it finds them, so if you do not see any error messages then all testing so far has been successful. Once you start testing MemTest will continue to test your RAM until you tell it to stop, or quit.
How many instances of MemTest: If you have a multi-core or multiprocessor machine you can make the memory test more effective by running multiple copies of MemTest at the same time. Start at least as many copies of MemTest as you have cores and then divide the amount of RAM to test between them equally.
How MemTest works: MemTest tests the ability of your RAM to store many different unique bit patterns, and to correctly hold those values over various periods of time. More traditional memory checking programs can only catch problems which show up immediately. MemTest catches both immediate errors and long term errors. The longer you run the program, the better the test against long term errors. If you can run MemTest overnight without errors then you can be sure that your RAM functions correctly.
NOTE: If you run MemTest and it only checks a few % of RAM over the period of an hour, this means you told it to allocate more RAM than is available. When this happens, almost all of the testing time is taken reading from the hard disk swap, which is a reasonable hard disk check, but not very useful for checking RAM. Select less RAM to check and try again.
In all cases if MemTest finds an error it will stop and report it to you. If you do get an error, you should consider replacing your RAM or at the very least verifying that your machine is correctly configured. Note that even ONE error is a sign of a serious problem - a correctly functioning computer can run MemTest for weeks with no errors.
If you do get an error, the next question is to determine how to fix it. The most common cause of memory errors is a faulty memory board. Unfortunately, due to variations in motherboards and chipsets, it is impossible to reliably locate the physical chip that is failing purely via software. It is still possible, however, to determine which DIMM is failing by elimination: Run the machine with just one memory board installed at a time; when errors are found the installed board is at fault. This is also a good diagnostic for another reason: sometimes the problem is really with the motherboard, and it will disappear if you have less RAM installed, or if the DIMMs are installed in different slots. If you have access to multiple computers, you should also try testing the "faulty" RAM in both to isolate whether the problem is the memory or some other component.
If you have more than one DIMM and you find errors with both, even when you test them one at a time, this suggests that your RAM is probably OK. Either your motherboard is failing, you are using memory timing settings that are too aggressive, or your RAM is not compatible with your motherboard. You can experiment with memory timing settings in your BIOS, which may allow you to use your RAM without errors at a small performance cost. Also check that you are using the proper voltage setting for your RAM (not all BIOSes let you set this). Please refer to your motherboard manual for information on this topic - HCI Design cannot provide specific recommendations for BIOS settings.
Another potential cause of memory problems is overheating - make sure your machine is well ventilated and try running the test again. If you've tried everything else, another possibility to consider is that misbehaving drivers can occasionally corrupt RAM (note that this is very unusual). Try booting Windows in safe mode, loading as few drivers as possible, and run the check again. Or, consider purchasing the Deluxe version of MemTest, which boots off of its own CD, eliminating any possible software cause of your faulty memory.
If you have any questions, please take a look at our FAQ page before contacting tech support.
The normal version of MemTest is a Windows program, and is free for non-commercial or home use. There are two other versions available:
The Pro version ($5) is a Windows program that extends the free version. It is tuned to the needs of users who diagnose the quality of RAM often, or on multiple machines. Features include:
The Deluxe CD package ($14) includes the Windows native Pro version. It adds a 32-bit and 64-bit version of MemTest that runs directly from a bootable CD. This version can be run on any PC and does not require any sort of installation. Use it to check the RAM quality of any PC, whether it has Linux, Windows, or no OS at all. Plus, since it does not load an OS, it can directly access and test all of your RAM. This is a great disk for computer technicians to carry around. It also uses the rate that memory is checked as a basic speed benchmark. This can be useful if you are trying different BIOS settings. Not only will MemTest tell you if your RAM is still stable, but it will also indicate if the tweaks you have made improve RAM performance.
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Questions about this product? Visit us online at http://hcidesign.com/memtest, or send your question to technical support (memtest64hcidesign.com). Please take a look at our FAQ page before contacting tech support.