RAM upgrade

Simple RAM question I think, perhaps more of an opinion rather than right or wrong.

I am upgrading over 200 Dell Optiplex GX520s (I know they are old, please dont suggest chucking them) to meet a min spec of 2GB RAM. Some will be straight forward as they have just a 1GB stick and a empty slot - so I'll just buy another 1GB stick.

The question I have is for the PCs that have 2 x 512MB sticks. Due to there only being 2 slots I know I will have to order 2GB sticks, but is there any reason why I shouldnt take just one 512 out and leave the other? ie upgrading the PCs to 2.5GB instead of 2. I am aware that best performance comes in using 2 of the same sizes side by side, but wondered if a 'mix and match' might cause issues??

Initially this is for an XP install but come September they will be Windows 7

Thanks in advance

Mix and match is fine and is no worse than just using a single chip. I highly recommend leaving in as much RAM as you can because the more you have the smoother Windows and the apps run especially when the machine has been up and going for a little while.

The one thing to watch for is if the old RAM is rubbish speed, 333 instead of 400 when the board and chip will actually suport 400, some don't. You want your RAM to be running at the highest speed possible as this can make a big difference. This assumes DDR, DDR2 is much better and pretty much all runs at an acceptable speed apart from the truely ancient stuff.

Thanks @SYNACK . The existing RAM is DDR2 PC2-5300, so I dont think I need to worry?

No should be fine but I would buy the 800mhz stuff for any new stuff as it is bound to be cheaper and more reliable when clocked down to that anyway. If the 1GB ones are that speed to I would probably look at yanking the 1GB out of one, populate both with the faster stuff and put the recovered slow dimm into another machine with an existing slow dimm. That way you will at least get full speed out of some of them. There again, just make sure that the MB and CPU actually support 800mhz before bothering with that on the grounds of a little extra speed. Matching the DIMMs like that is likely to yeild more stable machines though.

The memory controller will be dual channel - so would benefit from two matching sticks (only around 5% AFAIR) but this should still be of more benefit than unused RAM - depends if they will be running with that much RAM in use.

I would but 100s of 1GB sticks, then have 2x1GB in each machine. using 2GB and 512mb gives you more RAM, but im one for pairs of RAM, its faster (not massivley but faster), but as always depends on the cost of 1x2GB compared to 2x1GB. No point paying double for the same result.

I would also check the speed of the current RAM to the best the board supports, as you dont want new RAM slowed down by an old 512mb stick.