RAM chips don’t mix.

Question: I have a computer lockup problem after I added extra RAM memory. My original configuration was a 486 DX machine with 8 Megs of RAM. I upgraded to 16 megabytes when I installed Windows 95. Then I decided to add an additional 16 Megs. This is when the problems began.

If I ran two applications, the computer would lock up. I had to reboot to get going again. Thinking that the new RAM was the problem, I exchanged it but I had same problem. I found it highly unlikely that the second RAM replacement was also faulty. I pulled the first 16, which I had no problem with, and replaced it with the second 16. Programs ran well. It seems like my computer will not accept the second 16 Megs. Any ideas as to what the problem could be? –Tory

Answer: The problem seems to be RAM chips that are incompatible with one another. The motherboard is happy with either but not both together and stops functioning. It reminds me of my mom and my younger twin brothers, but let’s move on before I get banned from Christmas dinner this year.

“It is possible that the new RAM is 60ns,” said Kirk Reid, senior technician at CompuSmart in Edmonton. The abbreviation ns is short for nanoseconds which is a billionth of a second. Old RAM is typically rated 70ns or even 80ns.

“Many early machines (486 DXs and lower) will not allow mixing of speeds,” added Reid.

To check the RAM speed, open up your case (after disconnecting the power, of course) and look at the RAM chips. They’re usually oversized mini-boards shaped like sticks of Wrigley gum, that plug into motherboard slots at a right angle. Often, it’s easy to tell what speed the RAM is by looking for a long number with a dash in it on the memory chip. Something like MSC23236-70BS24A. In this example the RAM would be rated 70ns.

Typically, you’ll see speed ratings between 60ns, 70ns, through 100ns, with the lower number being the newer faster chips. Also, check to see that the new RAM isn’t EDO or Extended Data Output RAM. That’s a new kind of RAM that runs up to 15% faster if you have a Pentium with the Triton chipset. “Your machine will definitely NOT support EDO memory,” advises Reid. I just bought some RAM from Micron in the U.S. and it arrived with a tiny little sticker that said “EDO” on it. Yours may have some similar markings.

Reid’s CompuSmart co-worker Jeremy Schmuland suggests a few other options to consider: “It is possible that the original memory has tin leads and the newer RAM has gold leads, or vice versa.”

There have been considerable debates about this. The end result was that machines should not be installed with mixed RAM chips that have both types of leads.

Finally, check the motherboard manual that came with your computer. It will specify acceptable RAM configurations that will run on your machine.

If you still have no luck, a qualified technician might be able to spot the problem for about an hour’s worth of labor.