Memtest86 is considered by the majority of the hardware testing community the number one application when it comes to defective RAM sticks. The answer to the question regarding the working state of the installed memory modules comes fast with Memtest86 and that is what matters the most besides the certainty of the verdict.
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:
- Write a cell with a zero.
- Write all of the adjacent cells with a one, one or more times.
- 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.
Version 7.1 5/Aug/2016
- Fixed a bug in measuring CPU clock speed using HPET which could skew the clock speed results to unreasonable values. This may have caused issues during startup including extremely long loading times
- Added fallback mechanism to use the legacy PIT to measure the clock speed if the measured CPU clock speed using HPET is unreasonable
- Disabled code optimization for Test 12 due to reported freeze when running in parallel mode
- Fixed CPU selection mode not being set according to the results of the multiprocessor test during startup
- When switching to the next target CPU in Sequential/Round Robin mode, attempt to reset the target CPU if there was a failed attempt to switch the BSP
- When looking for SMBus devices for RAM SPD retrieval, attempt to look for any disabled SMBus devices to enable before enumerating the PCI bus
- Fixed cursor appearing for some systems during testing