Hardware Reference
In-Depth Information
•
Ultimate Boot CD
—
www.ultimatebootcd.com
Not only are these free, but they are available in a bootable 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 memory and other hardware required
for testing. These programs use algorithms that write 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 indicate the module that is failing should you encounter an error. Note that a version
of the Windows Memory Diagnostic is also included with Windows 7/8 and Vista. It can be found as
part of the Administrative Tools (mdsched.exe), as well as on the bootable install DVDs under the
Repair option.
The Ultimate Boot CD includes Memtest86 and several other memory diagnostic programs. Both the
Ultimate Boot CD and the Windows Vista and later install DVDs (containing the Windows Memory
Diagnostic) can also be installed on a bootable USB flash drive, which makes them much more
convenient to use. To create a bootable flash drive with the Ultimate Boot CD you would use the
ubcd2usb command as described in the “Customizing UBCD” page on the
www.ultimatebootcd.com
website. To create a bootable flash drive version of a Windows 7/8 or Vista installation DVD you
can use the Windows 7 USB/DVD download tool provided by Microsoft
(
http://tinyurl.com/4qfdm4x
). Note that although the tool has “Windows 7” in the name, it works on
Windows 8 and Vista discs as well. If you want to test the memory on a system that already has
Windows 7/8 or Vista installed, merely run the mdsched.exe command or open the Control Panel,
Administrative Tools and select the Windows Memory Diagnostic, which will allow you to restart
the system and run the test immediately or set the system to run the test automatically on the next
restart.
One problem with software-based memory diagnostics is that they do only pass/fail type testing; that
is, all they can do is write patterns to memory and read them back. They can'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 modules. 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
)
, CST (
www.simmtester.com
), and
Innoventions (
www.memorytest.com
). They can be expensive, but for a high volume system builder
or repair shop, using one of these module testers can save time and money in the long run.
After your OS is running, memory errors can still occur, typically identified by error messages you
might receive. Here are the most common:
•
Parity errors
—The parity-checking circuitry on the motherboard has detected a change in
memory since the data was originally stored. (See the “
How Parity Checking Works
”
section
earlier in this chapter.)
•
General or global protection faults
—A general-purpose error indicating that a program has
been corrupted in memory, usually resulting in immediate termination of the application. This
