Hardware Reference
In-Depth Information
example, most Intel motherboards use the Phoenix BIOS. Several beep codes are used in
that BIOS to indicate fatal memory errors.
If your system makes it through the POST with no memory error indications, there might
not be a hardware memory problem, or the POST might not be able to detect the prob-
lem. Intermittent memory errors are often not detected during the POST, and other subtle
hardwaredefectscanbehardforthePOSTtocatch.ThePOSTisdesignedtorunquickly,
so the testing is not nearly as thorough as it could be. That is why you often have to boot
fromastandalonediagnosticdiskandrunatruehardwarediagnostictodomoreextensive
memory testing. You can run these types of tests continuously and leave them running for
days if necessary to hunt down an elusive intermittent defect.
Fortunately,severalexcellentmemorytestprogramsareavailableforfreedownload.Here
are some I recommend:
•
Microsoft Windows Memory Diagnostic
—
http://oca.microsoft.com/en/windiag.asp
•
Memtest86
—
www.memtest86.com
Not only are these free, but they are available in a bootable CD format, which means
you don't have to install software on the system you are testing. The bootable format is
actually required in a way because Windows and other OSs prevent the direct access to
memoryandotherhardwarerequiredfortesting.Theseprogramsusealgorithmsthatwrite
different types of patterns to all the memory in the system, testing every bit to ensure it
reads and writes properly. They also turn off the processor cache to ensure direct testing
of the modules and not the cache. Some, such as Windows Memory Diagnostic, even in-
dicate the module that is failing should you encounter an error. Note that a version of the
Windows Memory Diagnostic is also included with Windows 7/Vista. It can be found as
part of the Administrative tools, as well as on the bootable install DVDs under the Repair
option.
One problem with software-based memory diagnostics is that they do only pass/fail type
testing; thatis,alltheycandoiswritepatterns tomemoryandreadthemback.Theycan't
determine how close the memory is to failing—only whether it worked. For the highest
level of testing, the best thing to have is a dedicated memory test machine, usually called
a
module tester
. These devices enable you to insert a module and test it thoroughly at a
variety of speeds, voltages, and timings to let you know for certain whether the memory
is good or bad. Versions of these testers are available to handle all types of memory mod-
ules. I have defective modules, for example, that work in some systems (slower ones) but
not others. What I mean is that the same memory test program fails the module in one
machine but passes it in another. In the module tester, it is always identified as bad right
down to the individual bit, and it even tells me the actual speed of the device, not just its
rating. Companies that offer memory module testers include Tanisys (
www.tanisys.com
),
