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MemTest86 is the original, free, stand alone memory testing software for x86 computers. MemTest86 boots from a USB flash drive and tests the RAM in your computer for faults using a series of comprehensive algorithms and test patterns.

Memtest86 is released under the terms of the Gnu Public License (GPL). Other than the provisions of the GNU pubic licence (GPL) there are no restrictions for use, private or commercial.

Explicit permission for inclusion of Memtest86 in software compilations and publications is hereby granted.

MemTest86 is a free, thorough, stand alone memory test for x86 architecture computers.

MemTest86 supports booting from both the newer UEFI platform and the traditional BIOS. When booting from UEFI, MemTest86 has access to additional services not available in BIOS including:

* Native 64-bit support
* No longer requires the use of the PAE workaround to access more than 4GB of memory. (PAE = Physical Address Extension)
* Mouse support, where supported by the underlying UEFI system. On older systems a keyboard is still required.
* Improved USB keyboard support. The keyboard now works on systems that fail to emulate IO Port 64/60 correctly. So Mac USB keyboards are now supported.
* Improved multi-threading support, where supported by the underlying UEFI system.
* Reporting of detailed RAM SPD information. Timings, clock speeds, vendor names and much more.
* Support to writing to the USB drive that MemTest86 is running from for logging and report generation. In all prior MemTest86 releases, there was no disk support.
* Use of GPT. (GUID Partition Table)
* ECC RAM support (limited hardware support, ongoing development)
o Detection of ECC support in both the RAM and memory controller
o Polling for ECC errors
o Injection of ECC errors for test purposes. (limited hardware only)
* DDR4 support (but we are currently having problems sourcing DDR4 RAM to test)
* Option to disable CPU caching for all tests
* Having a configuration file to allow settings to be pre-defined without the need for keyboard input. This can help with automation.
* Support for Secure Boot.
* Speed improvements of between 10% and 30%+. Especially for tests, #5, #8 & #9. This is the result more moving to native 64bit code, removing the PAE paging hack, switching compilers and using faster random number generation algorithms.
* Addition of 2 new memory tests to take advantage of 64bit data and SIMD instructions.

There are many good approaches for testing memory. However, many tests simply throw some patterns at memory without much thought or knowledge of memory architecture or how errors can best be detected. This works fine for hard memory failures but does little to find intermittent errors. BIOS based memory tests are useless for finding intermittent memory errors.

RAM chips consist of a large array of tightly packed memory cells, one for each bit of data. The vast majority of the intermittent failures are a result of interaction between these memory cells. Often writing a memory cell can cause one of the adjacent cells to be written with the same data. An effective memory test attempts to test for this condition. Therefore, an ideal strategy for testing memory would be the following:

1. Write a cell with a zero.
2. Write all of the adjacent cells with a one, one or more times.
3. Check that the first cell still has a zero.

It should be obvious that this strategy requires an exact knowledge of how the memory cells are laid out on the chip. In addition there are a never ending number of possible chip layouts for different chip types and manufacturers making this strategy impractical. However, there are testing algorithms that can approximate this ideal and MemTest86 does just this.