Desktop DDR rarely exceedes 64bits(you have to combine more than one dimm). Since RAM is a parallel bus that means 64 conductors that have to be impedance and l

Desktop DDR rarely exceedes 64bits(you have to combine more than one dimm). Since RAM is a parallel bus that means 64 conductors that have to be impedance and length controlled. GPUs use >192bit busses, with 512bit in the high performance GPUs. So that's now 512 conductors. 512 conductors that have to be exactly the same length. Make them longer you'll say- now you just lost your high memory clocks to propigation delay and parasitics. Seeing the problem?