mixing memory speeds - DDR

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my mobo recommends ddr PC2700.

if i have an existing ddr module at PC2700, but want to add another ddr module which is higher PC rating, will this fail or will this still be compatible?

cheers.

 

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Depends, if you are putting in a higher frequency RAM then it may have to run with sticks at the same frequency. Some RAM is backward compatible though.

Check out Crucial's RAM Advisor and they should be able to tell you what the score is.

HTH

Edit: Just noticed they have a funky little system scanning tool as well!

 

The first lesson i learnt when i started playing with memory upgrades from a senior tech... DONT MIX SPEEDS it will only cause problems in the future or instantly!

 

I always buy my RAM in matched pairs. I know plenty people who run mixed speeds and its stable, but i wouldnt do that personally. If you do run mixed speeds, then the system will run at the slower speed RAM.

 

I'll mix them. The way that I look at it is that I would rather have more memory at the lower speed than less at the higher.

I suppose though it depend on what the computer is going to do.

 

To be honest it all depends on the RAM and teh Mobo they go in. I've mixed RAM and sometimes its worked and been stable for years, other times it causes the system to do strange things randomly (though this could just be windosw) and at others, it just plain don't work from the start.
What i have found is that in most mobos, the slower RAM has to be in the first banks and the faster in the last banks for it to work. The other way round in the same mobo and the system wont boot.

 

check the manual and read the mobo website, if you put higher ram in a mobo thats not designed for it might not even boot, and you have wasted your cash.

hell, might be better to save the cash for a better mobo, put the old ram in and save for the higher speed ram later..

 

As the others have said, you could have weird problems happen. Check the mobo manual to see if they support mixing speeds. If not, get the same speed memory if at all possible.

 

For dual channel always get matched pairs. But plain DDR400 *usually* works fine at 333..

The modules themselves report the speeds they support. Here's an example from my laptop which uses PC2700/DDR333 (166Mhz FSB):



As long as the timings match it WILL work. If one is slower than the other always put the slower module first (no guarantees in that case though.)

 

Again as stated before, I personally always buy the same RAM in matched pairs. If you want it to go faster thats fine.... I bought some OCZ @ 4-4-4-12 timings, but now tweeked to 3-3-3-10. runs alot quicker now too.

 

What's really funny is DDR400 and DDR333 often come off the exact same assembly line nowadays. The modules that test out at max speed get stamped DDR400 and those that don't get sold as DDR333.

 

This is standard in the electronics world. I remember being told just exactly that very many years ago.

In addition, it is not unkown for parts to be marked down in speed if there is a shortage of that speed in the market, and a demand for them.

Harry.