Go to this link
http://www.crucial.com/store/listparts.aspx?model=775Dual-VSTA
Then filter by DDR2 and 2GB
The RAM should be populated in matching DIMM pairs with same capacity, same speed, etc. to take best advantage of the system's DUAL CHANNEL memory architecture.
Take a look here too..this should also work.
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231098
The options are endless ..
Let us know how it goes.
VAPCMD
Ok, so i've looked on CNet to find out which motherboard i have, and after downloading AIDA32, and finding out, i know i have this one:
http://www.asrock.com/mb/overview.asp?Model=775Dual-VSTA
I currently have 1GB DDR2 667mhz pc5400 ram. 1 stick.
Now, i think the max for my mobo is 2gb, so i could get one stick more of the same ram, but i was wondering if i could upgrade to a better ddr? higher mhz? pc5400+ ??
Wondering if you guys could help me pick the best 2 sticks i could put in to optmize the performance of my ram in my system.
Thanks! (I use this for gaming!)

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