Memory is quick and easy to change, and because the result of buying new RAM is often a performance gain, it's one of the most common upgrades carried out on a PC.

But things don't always go smoothly, and faulty RAM causes its fair share of heartache. Repeated 'Stop' errors, freezes and other crashes may well be caused by duff memory.

Even if you've never upgraded your RAM, if your PC has difficulties like these, memory may still be the problem. Substituting it with some new RAM may help, but if your memory isn't actually the culprit, the expense may not be worth it.

To make sure that the RAM is at fault, you need to run some tests. The most efficient is MemTest86 – grab it from www.memtest.org.

Go to the Memtest site, choose 'Free Download' and opt for the latest version in ISO image form. This will be downloaded as a ZIP archive, so browse to it and double-
click the file. Choose 'Extract All Files in Windows Explorer', then follow the wizard to extract the ISO file.

Use a free CD-burning program like CD Burner XP to burn the ISO image to CD. Launch the program and go to 
'File' > 'Write Disc from ISO File' before finally browsing to the ISO image and clicking 'Write Disc'.

See the walkthrough below for details on how to run the program.

Memtest86 is very thorough, and because it runs outside Windows you can be sure that you're checking RAM addresses that might normally be occupied by Windows components (and thus are likely to produce crashes).

Running continuous testing for a couple of hours should ensure that you've checked each address multiple times. The longer you run the test, the more accurate your results will be.

If you get errors reported and you have multiple RAM modules, remove all but one and run Memtest86 again. Swap your other modules in and retest to confirm which is causing the issue. This will save you from replacing more memory than necessary.

Once you've identified the faulty module(s), you can start looking for replacements. Your motherboard manual or PC documentation should tell you the specification of the RAM you need, but useful paperwork isn't always to hand.

Memory specialist Crucial provides a useful online tool to identify the type of RAM you need. You can either use its scanner tool (if you use Internet Explorer and you don't mind having your system probed or the possible privacy implications that this might have) or you can use Crucial's own Memory Advisor product.

This is a simple database in which you select the manufacturer, product line and model number of your off-the-
peg PC, laptop or motherboard. Once you've found out the specification for the memory modules needed, you can shop with Crucial if you like, or you can browse Kelkoo and others to find the best price.

Thoroughly test existing memory

1. Boot from CD

Memtest 1

Once your Memtest86 ISO file has been burned to CD, restart your computer so that it boots from this disc. You may need to enable CD booting in the BIOS or select the Boot menu at startup for this to happen. You should boot directly into Memtest86 and start testing.

2. Run automatic tests

Memtest 2

Memtest86 automatically runs a number oftests on your RAM. If all is well, the memory should pass all of these tests. You can run continuous tests to detect intermittent problems. If errors are reported, you may need to replace one or more of your memory modules.

3. Configure specific tests

Memtest 3

You can configure the program by pressing [C] while it's up and running. This opens a menu that gives you the full choice of tests to run and enables you to set a memory address range to test. That option may be useful if you're getting intermittent problems.

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First published in PC Plus Issue 296

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