My friend's looking to upgrade his pc by an extra 1gb. He has a Dell Poweredge SC420 and his first slot of 4, has 256mb in it. Memory advisors have said DDR2 240 pin memory is required, however a few things confuse me here.

Kingston's memory site says "Virtually any configuration up to 4GB can be reached using Kingston's 256, 512MB, and 1GB modules IN PAIRS."

Now what does it mean by in pairs? Does that mean I have to add another 256mb to the second slot to go with the first? Assuming that the pairing works 1st with 2nd slot, 3rd with 4th. I want to put 1gb in, so can I get 'round this pairing by putting in 1gb in the THIRD slot, so it's in a 'new pair'? Or does the 1gb have to be of the exact same type as the 256mb? Even though it should be compatible?

Crucial recommends PC2-4200 memory which is faster than what I'm buying, PC3200 DDR2, but I'm assuming it's backwards compatible? So the PC3200 will work if a PC2-4200 will work?

Need advice on this asap, thanks.

Your friend's PowerEdge server (it's not one of Dell's desktop PC ranges) must be able to support standard single-channel DDR RAM if it only has one 256Mb module in it at the moment.

DDR2 RAM is "dual channel" memory, which means that you use it in pairs and it performs faster as information can travel along either of the two channels, whichever one isn't busy. Some standard DDR RAM works like this as well (we have 6-month-old Dell Optiplex desktops at the office that work the same way). This is a good performance enhancement but it does take us back 10 years to when the early Pentium systems had to have 72-pin SIMM memory fitted in pairs - one module on its own simply wouldn't work.

So it seems, from what's already fitted, that the system supports both single channel standard DDR RAM and also dual channel DDR2 RAM, which seems a little odd. I'm going to see if I can get a confirmation of that and, if I can, I'll be back shortly

A search on Crucial Memory's web site (http://www.crucial.com/uk/store/list...C420&submit=Go) tells pretty much the same story. It says that the SC420 is supposed to have DDR2 memory fitted in pairs. Your friend could go for a 1Gb kit (2 x 512Mb modules) in DDR2 533MHz format (PC-4200). DDR2 667MHz memory (PC-5300) would also work but is 25% more expensive and is unlikely to give any benefit.

Hope that helps

As to why the server's currently running with only 256Mb, I'm afraid I have no idea!