Most memory problems appear as soon as you install a new module. However, several circumstances such as a power surge, can cause a RAM chip (one of the integrated circuits mounted on a memory module) or a whole module to fail. If that happens, you might want to run a diagnostic test. The Power-On Self Test (POST) tests the memory every time you turn on the computer, but sometimes it's useful to run a more detailed series of tests.
As part of its standard startup routine, the BIOS performs a complete test of the computer's RAM. Some BIOS menus allow the user to bypass the memory test to save time, and others might hide the results of the memory test behind a splash screen that fills the screen with the computer maker's name; but the POST can be a useful tool when you suspect that your computer has a memory problem.
For more information about the POST and the BIOS, see Chapter 8.
If your computer fails the POST memory test, or if you want more details about a possible memory problem, several other memory test programs are available.
Both Memtest86 (described earlier in this chapter) and Microsoft's Windows Memory Diagnostic program automatically load and run from a boot floppy disk or CD. They each perform a series of tests on the computer's RAM, and identify the addresses of any problems they find.
You can download Microsoft's Memory Diagnostic program from this address:
It's not possible to remove or repair the individual chips mounted on memory modules, so you must identify the module that contains the failed bits and replace it with a new one. If your computer contains only one module, there is no doubt that the bad RAM is on that module.
If the computer has more than one module, isolate the bad RAM by removing modules one at a time (or in pairs if the motherboard requires matched pairs) and running the test again. When the remaining modules pass the test, you know that the problem is in the one you just removed. The Microsoft program also includes a View Errors by Memory Module that identifies the physical location of a memory failure.