Renfeld

in my nf7 socket A bios where it gives a choice of mem interface...IE:4 to 2,4 to 3,4 to 4,5 to 4,5 to 5,4 to 6,5 to 6,6 to 6 etc I know what the uneven settings do-they allow non syncronis mem timing with cpu, but what is the difference with the syncronis timings AKA 4 to 4,5 to 5,6 to 6...?when I set to auto it gos to 6 to 6....