RAM for ASUS P4P800 & P4VP-MX

>P4P800 has 512 Mb, DDR400 and I want to put in extra 512 Mb. This mobo has the Dual-Channel Mamory feature, Woudl it >be OK just to add another 512 Mb DDR400 stick or their should be some other considerations?

YES, but check to make sure the new RAM has the same CAS Latency (2.5, 3, etc...)

>P4VP-MX has 256 Mb, it has 533MHz FSB, but DDR400 memory stick (it said on the stick 400, DDR). I'm supposed to have >133MHz sticks with my FSB and my first question about this mobo is how bad that I have FSB 533MHz and that I use higher >frequency memroy?

With A 533MHz FSB mobo you should use DDR400 memory

>another one is, can I add another 512 Mb or it should be consistent and should be either two 256s or two 512s?

It is best practice to be consistent and use 2 x same Mb, but you can add memory stick of different sizes as long as they match in every other way, eg: CAS Latency, buffered/unbuffered, parity, etc...  Also, if you are going to add a stick of different size, put the higher Mb stick in the first memory slot.

>if I have DDR400 256, can I, say, add 256 Mb, but not DDR400, but someting like DDR333 or DDR266?

NEVER mix memory speeds, it won't work, eg: DDR400 + DDR333 will not work together.

With dual channel it is always best to just order another stick of exactly what you have in there to the model.  Sometimes differing companies will have differing regulations and the memory wont match exact.  If you buy another stick of the same model number from the same company all problems are ruled out.  This is what I did with my p4p800se MoBo and all was well, but it seemed slower when I added another manufacturers RAM that supposedly matched.

Wildstar1869 - not related to this question, but with regard to your comment "... it seemed slower when I added another manufacturers RAM that supposedly matched..." ==> If it was in fact slower, then it's almost certain in that case that the SPD info was not identical, so the system operated in single channel mode.

Also "... If you buy another stick of the same model number from the same company all problems are ruled out." ==> It would be nice to think that; and with the major companies (Crucial, Kingston, etc.) it generally is true; but with many lower-tier suppliers this is not always true.   They often change suppliers, and even the same model number memory will not work in dual-channel mode if you happen to get two modules from different suppliers with any variance in their SPD's.    That's one reason most memory companies now offer "matched pairs" when you buy the memory -- this absolutely eliminates any possibility of this issue.

thanks a lot guys,

so, taking into consideration of what you said, I can buy two DDR400 512 Mb memory sticks (check if they support dual-channelling), put 'em in my p4p800, and the one DDR400 512 Mb from p4p800 add to my p4vb-mx, is it right?

a little bit consired with CAS Latency, since I'm not sure what it is for my current sticks and I'm not sure they put this info on them.

thanks again,
yurich

"... so ... I can buy two DDR400 512 Mb memory sticks ... put 'em in my p4p800, and the one DDR400 512 Mb from p4p800 add to my p4vb-mx, is it right?" ==> Yes, that's a good plan.   Buying a matched pair will guaranteee no issues with dual channel support, and the 512mb stick should work fine in the p4vb-mx.  You can confirm that (just to be sure there are no spurious timing issues) by just moving the 512mb stick to your p4vb-mx now :-)

Don't worry about the latency -- it should be read by the system (it's reported by the memory's SPD) and set correctly.  If you do have any issues, you can adjust the setting in the BIOS -- but this is rarely required.

thanks, and moving my old 512 to my other computer, i can have 768, right? since I'm going to keep 256 as well.

Yes - you'll have 768mb in the P4VP-MX and 1GB in the P4P800 after you do what you've suggested above.   ... and the P4P800 wll be running in dual channel mode.

excellent, thanks a lot