512 has worked well on our PC too. I know on some PC bords the memory has to be matched in pairs. I built our desk top 1 1/2 years ago. Spent weeks reading about all the best rated and faster parts. Works well and is faster than a off the shelf lap top with a higher rated speed. The nice thing about building your oun PC is you have all the drivers seperate and an orignal ver of windows. The PC boards you buy tend to be more flexible. The PC companies just use what ever parts they get they best deal on. If you want to make changes it can be hard with off the shelf units.