Mixing PC2100 DDR and PC2700 DDR

[phantomtres]

My computer had 2-128 MB of PC2100 DDR ram. I replaced one of them with a 512MB ram. Since I had the extra 128MB I decided to install it in my sons computer. His has the AMD Athlon XP processor, he already had 512MB of PC2700 ram and a empty slot so I installed the 128MB PC2100 ram in his computer. Instead of reading 640MB of ram it reads 576MB of ram. Is this because the 512 ram is PC2700 and the 128 ram is PC2100 and can that cause any problems?

[fudtone]

that is strange indeed... It sounds like the different ram is confusing the bios...What kind of MB is it?

[digitalfreedom64]

Does the motherboard have onboard graphics?

[rcvalencia9]

The onboard video card of the motherboard is using the memory. Its called shared memory. It uses 64 MB maybe. 576 MB(Physical Memory) + 64MB(Shared Memory) = 640 MB. That's common in laptops and notebook PCs. But never heard it from desktops. I might be wrong.

[doubledragon5]

Installing two different types of ram ie: pc2100 pc2700 and two different sizez will cause nothing but problems.. Always use matchec pairs ie: 2 Pc2100 or PC 2700 2x 128 or 2x512.

[fudtone]

I have never had a issue useing 2 speeds/sizes of ram...only that it would run at the slower speed.

[digitalfreedom64]

That's the only thing that will be caused. The higher speed ram will downclock to match the other ram. About the only thing that may cause problems is if the ram sticks hae different latencies.

[fudtone]

IF the MB was pulling the SPD from the faster stick it could get a bit wacky but I would only think this would lead to instability, not a bad reading... you may try to swap the position of the ram however its always recommended to run the bigger first. This also is only performance related and should not cause this result.

[doubledragon5]

My imput was used, because the first time I did this, I got the blue screen of death. then again I was runing Win98.

[KilluminatiStyle]

I had a similar issue with an older Gateway machine. I had installed 2 sticks of 128 PC2100 but the thing would only show 128 total. CPUID also only showed 64MB in each dimm. The problem was fixed with a BIOS flash although Gateway made no mention of there ever being an issue with ram in the BIOS release notes.

As for the 2 different speeds your using.... this should by NO means cause a problem in any of today's systems as the MB will do as a few people mentioned above and use the slower of the 2 sticks as the rated speed for both.

[glc]

His computer is only reading one side of the 128mb stick. The 128mb stick is not compatible with his motherboard in the configuration you are using. It may read the whole thing if you swap slots. Pull it out of there, the slight difference between 512mb and 640mb is not worth the big speed hit you are taking slowing the whole thing down to PC2100. You also might consider pulling the remaining 128mb out of yours and either keeping the pair of 128's around for troubleshooting or try to sell them.