The question is which will give me better performance? the 2GB 4x512MB 667Mhz or 3GB 2x1GBx800+2x512MBx667. Will performance change according to the slot they are put in? Thanks!

 I want to say the 4x512, just becasue you will have all matching dimms. The other set up you have the 800 speed stuff will get downgraded to run at 667 to match the speed of the other ram. Either way your filling at 4 slots and i have heard that it will slow them down some if your running all 4 dimm slots.Although with running 3gb you will get more space.

Thanks. So, whats the best set up possible? 3x1GB 800Mhz so i dont use the fourth slot(My mobo doesnt support more than 800Mhz) But in that set up DualChannel would only be enabled for the first pair and the third stick would run Single Channel?

 I would go for 2x2 if you could. but if you did go with 3x1 then i think what you said about the dual channel would be correct. but im not 100% on that.

If i go for the 2x2 setting, my OS (XP 32 bits SP3 Pro) wont recognize all 4 GB, i know; but How much will it recognize? Would you recommend me to switch to Vista Ultimate 32 SP1?

PS: I use my PC mostly for gaming.

urielsd:

If i go for the 2x2 setting, my OS (XP 32 bits SP3 Pro) wont recognize all 4 GB, i know; but How much will it recognize? Would you recommend me to switch to Vista Ultimate 32 SP1?

 

PS: I use my PC mostly for gaming.

This article was pretty insightful and tries to address the question you posed about how much memory and which configuration you should use.

http://www.bit-tech.net/hardware/2008/07/08/is-more-memory-better/1

The reason it won't recognize all 4GB is because you are using a 32-bit OS; it doesn't matter if it is XP Pro of Vista. You need a 64-bit OS. The reason is explained in the article too.

Thanks, everyone. RyuGTX, thanks for teaching me that limit of the 32 bit OS. I use my PC mostly for gaming, which will perform better with 4GB 800Mhz(2x2): XP 32, XP 64 or Vista 64? And also, Do you think soon to be released games will be XP 64 compatible or Vista 64 compatible?

Specifically from a software/game standpoint your best bet (due to the more mature driver-base) would probably be XP-32bit. Vista-32 would be fine as well but it comes with more weight so more of your RAM would be used for system services/processes etc....

That is to say, Vista or XP 64bit will not perform well...there are just some minor software compatibility issues....

If you are using a 32-bit OS your system will probably recognize at least 3GB (sometimes a titch more) and if you go 2x2GB as DER had mentioned the matching pair will overall help your performance even though some of it (your RAM) may not be recognized by the OS..

Ok. Thanks a lot for your help ice91785, and to the rest of you as well. I will stick for now with XP 32, and buy 2 sticks of 2GB 800Mhz each.