Why do most pcs duplex ddr3 ram

[thirtywest]

When maximum PC magazinne builds their super machine they always use a motherboard that only duplexs the DDR3 ram. Why not use one capaple pf triple mixing ddr3?

 

[lothdk]

If by duplexing memory you mean they use 2 sticks of memory modules, then that is because most CPUs support dual channel (memory in pairs of 2 for optimal performance) so 3 sticks would give worse performance.

The first generation of i7 on the socket 1366 supported tripple channel memory and its replacement socket 2011 supports quad channel.
For normal use (and price) any AMD or mainstream Intel setup will get the best performance running with dual channel memory ie 2 sticks or 4 sticks.