I have AMD Athlon X2 3600+, Asus M2NPV-MX motherboard & 3.5 GB (2GB+1GB+512MB - 667MHz) of RAM. With having four DIMM slots, & loaded with such amount of memory with mounted in Dual-Channel mode (e.g. A1+B1, A2), BIOS states memory is in 64-Bit sengle channel mode. First, I Tried to play around with all the slots with paired sticks but nothing changed. I got my self friend's 1.5 GB (1GB+512MB) & tried then, & things have changed for 1GB of paired modules. But for the 512MB modules. Also, tried 2GB pair & it worked in dual channel mode as well. Is that the case here, as if ONLY sticks with same size will work in Dual-Channel mode & NOT in either way! Please help .