(^150) PC Hardware: A Beginner’s Guide
However, if a memory error occurs after the system has booted, the operating system
willusuallydisplayanerrormessage.Hereareafewofthemorecommonerrormessages
you will see for memory errors on a PC:
Divide by zero error This error usually means that an operation has returned
a bad value, a running program has a very serious code flaw, or some operation
is working with a value that is too large to fit into one of the CPU’s registers.
This is likely a soft error, but attention should be given to any future errors
of this type.
General protection fault A running program has attempted to address
memory outside of its allotted space. This type of error can be either a hard
or soft error. A program may have a code flaw or there may be a bad patch
of memory on the PC. Typically, the offending program is terminated or the
whole system halts. If this error occurs more than once in a short timeframe,
it is time to use a memory testing tool to test the system.
Fatal exception error The operating system, a running program, or a device
driver has passed an invalid instruction to the CPU, or a bad memory location
was accessed. This error is usually caused by faulty memory and should be
checked out.
Software Diagnostic Tools
Because memory errors can be intermittent and very difficult to isolate and diagnose, it is
always a good idea to have a memory diagnostic program. As mentioned earlier, one of
the most popular programs of this type is the POST (Power-On Self-Test) program that is
included in your PC’s BIOS startu putilities. The POST does a number of memory tests
each time the system boots. It performs read and write tests to all of the memory it detects
and then compares its memory test results to previous POST results. Any difference in
the memory tests is dealt with like a memory error and it is signaled with a bee pcode or a
text message.
However, the POST is not able to test for future failures or performance problems in
memory. These tests are performed by memory diagnostic software, such as DocMemory
from SimmTester (www.simmtester.com), Memory+ from TFI Technology (www.tfi-tech-
nology.com), or Gold Memory from Goldware CZ (www.goldmemory.cz). These programs
are good tools for tracking down soft errors, because they can run continuously for hours or
evendaystofindthesourceofatransientmemoryproblem.Agreatsitewithanarrayofsoft-
ware diagnostic and troubleshooting tools is TweakFiles.Com (www.tweakfiles.com).Memory Testing Tools
SIMM and DIMM memory testers thoroughly test a memory module at different speeds,
voltages, and timings to determine if all of the memory cells (bits) on the module are