New Memory Controller: More Transistors, Higher Integration, Highest Efficiency
The battle for the most efficient memory controller is also the battle for just how fast your chip is going to be. Unlike the CPU, memory controller is without any doubt the most important part in a GPU. Without it, the units will starve and that was one of reasons why Intel Larrabee and ATI R600 were such failures - execution units were starved.
With Kepler, NVIDIA kept their policy of "1st gen memory controller is ok, 2nd gen kills the competition" and from the looks of it, the engineers scored once more. AMD has the natural advantage, since the company actually creates the GDDR memory standards.
Fermi had a fairly efficient memory controller, but you could not drive the memory as efficient as four generations of GDDR5 memory controllers on AMD GPUs (Radeon HD 4000, HD 5000, HD 6000, HD 7000). NVIDIA sticked to GDDR3 until the very end and then switched the boat with the first Fermi, the GeForce GTX 480. Unfortunately for NVIDIA, the company had multiple issues with the silicon and could not dedicate time and resources to optimize the performance on the part.
With Kepler, memory controller was in the focus and the result is expected - highest stock clock for GDDR5 memory by quite a margin: GTX 680 has memory operating at 1.50 GHz QDR (Quad Data Rate) i.e. 6000 effective MHz. By comparison, Radeon HD 7970 has memory operating at 1.375 GHz QDR, i.e. 5500 effective MHz.
Thus, GK104 has 256-bit memory interface and almost beats the GF110 Fermi (GTX 580), which utilizes 384-bit memory interface. According to company representatives, overclocking the GDDR5 memory will also be quite an interesting experience, with the first reports coming from overclockers reaching 1.8GHz QDR i.e. 7.2 "GHz". With 256-bit interface that yields 225GB/s - still short of 257GB/s achieved by AMD Radeon HD 7970, but nevertheless impressive.
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