Fel i memtest86

Troubleshooting Memory Errors

Please be aware that not all errors reported by Memtest86 are due to bad memory. The test implicitly tests the CPU, L1 and L2 caches as well as the motherboard. It is impossible for the test to determine what causes the failure to occur. However, most failures will be due to a problem with memory module. When it is not, the only option is to replace parts until the failure is corrected.

Once a memory error has been detected, determining the failing SIMM/DIMM module is not a clear cut procedure. With the large number of motherboard vendors and possible combinations of memory slots it would be difficult if not impossible to assemble complete information about how a particular error would map to a failing memory module. However, there are steps that may be taken to determine the failing module. Here are four techniques that you may wish to use:

1) Removing modules
This is simplest method for isolating a failing modules, but may only be employed when one or more modules can be removed from the system. By selectively removing modules from the system and then running the test you will be able to find the bad modules. Be sure to note exactly which modules are in the system when the test passes and when the test fails.

2) Rotating modules
When none of the modules can be removed then you may wish to rotate modules to find the failing one. This technique can only be used if there are three or more modules in the system. Change the location of two modules at a time. For example put the module from slot 1 into slot 2 and put the module from slot 2 in slot 1. Run the test and if either the failing bit or address changes then you know that the failing module is one of the ones just moved. By using several combinations of module movement you should be able to determine which module is failing.

3) Replacing modules
If you are unable to use either of the previous techniques then you are left to selective replacement of modules to find the failure.

4) Avoiding allocation
The printing mode for BadRAM patterns is intended to construct boot time parameters for a Linux kernel that is compiled with BadRAM support. This work-around makes it possible for Linux to reliably run with defective RAM. For more information on BadRAM support for Linux, sail to http://home.zonnet.nl/vanrein/badram

Sometimes memory errors show up due to component incompatibility. A memory module may work fine in one system and not in another. This is not uncommon and is a source of confusion. In these situations the components are not necessarily bad but have marginal conditions that when combined with other components will cause errors.

There have been numerous reports of errors with only tests 5 and 8 on Athlon systems. Often the memory works in a different system or the vendor insists that it is good. In these cases the memory is not necessarily bad but is not able to operate reliably at Athlon speeds. Sometimes more conservative memory timings on the motherboard will correct these errors. In other cases the only option is to replace the memory with better quality, higher speed memory. Don't buy cheap memory and expect it to work with an Athlon! On occasion test 5/8 errors will occur even with name brand memory and a quality motherboard. These errors are legitimate and should be corrected.

I am often asked about the reliability of errors reported by Mestest86. In the vast majority of cases errors reported by the test are valid. There are some systems that cause Memtest86 to be confused about the size of memory and it will try to test non-existent memory. This will cause a large number of consecutive addresses to be reported as bad and generally there will be many bits in error. If you have a relatively small number of failing addresses and only one or two bits in error you can be certain that the errors are valid. Also intermittent errors are without exception valid. Frequently memory vendors question if Memtest86 supports their particular memory type or a chipset. Memtest86 is designed to work with all memory types and all chipsets. Only support for ECC requires knowledge of the chipset.

All valid memory errors should be corrected. It is possible that a particular error will never show up in normal operation. However, operating with marginal memory is risky and can result in data loss and even disk corruption. Even if there is no overt indication of problems you cannot assume that your system is unaffected. Sometimes intermittent errors can cause problems that do not show up for a long time. You can be sure that Murphy will get you if you know about a memory error and ignore it.

Memtest86 can not diagnose many types of PC failures. For example a faulty CPU that causes Windows to crash will most likely just cause Memtest86 to crash in the same way.