- September 22, 2015 at 12:34 pm #71235Lil’ ½ DeadMember
We’ve been collecting data on memory bandwidth for some time now – of course we have – but one of the big questions hanging over Skylake is what the DDR4 support really brings to the table. It’s also worth comparing four generations of memory controllers – two dual-channel and two quad-channel – and seeing what the weaknesses and strengths of each one are.
With all that in mind, we compared Intel’s Ivy Bridge-E (quad-channel DDR3), Haswell (dual-channel DDR3), Haswell-E (quad-channel DDR4), and Skylake (dual-channel DDR4) at a variety of speed grades in synthetic testing in AIDA64 to isolate raw memory bandwidth. You may have heard by now that Skylake has a very robust memory controller, and that’s turned out to be true as you’ll see.
The following CAS latencies were used for each speed grade:
One crucial thing to point out with DDR4 is that it has an oddball “CAS latency hole.” You’ll notice we jumped directly from C16 to C18; C17 isn’t officially supported. The result is that there is a substantial jump in CAS latency moving up to 3466MHz that needs to be ameliorated, amusingly enough, by driving the memory at even higher clocks.
Skylake’s memory controller is something else entirely. We’ll need to see how it handles DDR3L – and we’ll be testing that in greater detail soon enough – but it has none of the scaling hiccups any of its predecessors have. Skylake’s memory controller is incredibly robust, and Skylake seems to overall be more efficient with memory in general. Second, DDR4 just doesn’t have the latency issues the transition from DDR2 to DDR3 did. In fact, it’s only when you’re making the C16 to C18 jump that overall latency starts to creep up, but that’s solved almost immediately by just going to the next speed grade. Ultimately, DDR4 draws less power, runs cooler, and delivers more bandwidth-per-clock than the venerable DDR3, and it has the scaling headroom that DDR3 lacked in both capacity and raw bandwidth. In other words, it’s a worthy successor.
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