Why can't I get the CAS 2-5-2-2

I have two Kingston DDR266 256M memories, and have them run stablely on Linux and Windows XP.
Today, I bought the third Kingston DDR266 256M memory. But when I set it up on the mobo, the machine will reset at the Windows XP login window, as well as the failure to load Linux's X window.
So I set the CAS to 2.5-5-2-2, and everything is OK.
It's curious that I can have any two of them work on CAS 2-5-2-2.
Who can tell me whether three memories are less stable than two? Why?
Thanks!

It's the third stick. It apparently can't run C2 so it's hindering the other two. Memory only operates as fast as the slowest stick.

~THT

Anytime you run more sticks of ram, or more ram total you load the memory bus more heavily and and generally lose clock rate or the ability to run as tight of timings as you would with less memory. Your Kingston is only rated at cas 2.5 anyway, so it is not terribly surprising you have to back the timing off with the addidition of the third stick.

Because of this tendancy most PC2700 (333MHz DDR) chipsets are only validated for 333MHz memory operation with two sticks in the machine. While almost all include at least a third dimm socket, if you are trying to maximize the memory's clock rate or timings it is best not to use it. In fact most times the best overclock comes from using a single 256MB module. As ram quality increases this tendency is not as pronounced as it used to be.

Top Hat Theater said:

It's the third stick. It apparently can't run C2 so it's hindering the other two. Memory only operates as fast as the slowest stick.

~THT

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Chances are very good that if you put the third stick in by itself, or with only one of the other sticks, it will run cas2. Loading the bus more heavily is the likely culprit rather than any shortcoming of the third stick.

larva great explanation. as usual your posts offer more insight and most importandly correct and well explained insight than just about anyone here. kudos

snvpa said:

larva great explanation. as usual your posts offer more insight and most importandly correct and well explained insight than just about anyone here. kudos

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Oh sure! Insult me! j/k

It seemed like the most probably explanation as that's what generally happened to me when running more than one stick.

~THT