I have a Gigabyte motherboard running a socket 426 Sempron 2200 mghz with two 512 DDR 400 OCZ dual channel modules. Is it possible to add a second pair 2x1 gb (G. Skill) to have 3 gb total? I am running W7 32 bit.
You have the slots? Then it should be possible. The only thing you would need to worry about are voltage settings and timings (for compatibility with your existing memory) and module density (compatibility with the motherboard). What's the model of your motherboard (it should have it printed on a sticker or silk-screened to the actual board somewhere). That will be a big help.
However, assuming the memory is compatible, I'm going to say replace the 2x512 with the 2x1GB. With a socket 426 and Sempron, I don't think memory capacity will be your biggest hindrance. Bumping from 1GB to 2GB might just be enough of a performance boost (and then you don't have to worry about matching your old memory timings and voltages with your new).
Sure.. If you can find and afford them and your motherboard has enough slots to accomodate them.. However, filling all memory slots and mixing brands is not a recommended practise but it works out ok most of the times.. For how much price are you getting the RAM sticks.? Btw, i hope you don't mind me saying this but your system sounds ancient for todays typical usage scenarios..
The motherboard is a GA-7N400 Pro and the modules are OCZ 512 kb 2.6v.
I am aware of the matching problems because I have some old Kingston modules that won't run in conjunction with the OCZ's. Well, that's not entirely true because they do run but my system is so unstable that it crashes all the time.
I realizhe that this thing is a dinosaur, but I only use it for internet and backup. My main machine is a P8400 Lenovo ThinkPad that is flawlessly reliable.
I could probably find another 2x512 for less than $50 at Newegg which may be enough of a boost Will running 2.5 v with my 2.6 v OCZ's cause a serious problem? You can get a pair of Corsair dual channel there for $46.
Well, just to answer some of your questions, you can probably run your 2.6V OCZ's at 2.5V just fine (use memtestx86+ to make sure its stable). Just make sure this is what is actually occuring, don't buy a 2.5V and find out later it was running them at 2.6V.
As for the timings, they should be acceptable. The system will use 1 set of timings, and both sets are so close they should run fine at either set (use the slower 2.5-3-3-7 just to make sure).