Memory subsystem performance
Before we dive into our real-world results, it's worth revisiting how much data each of these CPUs can move around from main memory and what the latencies associated with those actions are. To get that picture, we rely on AIDA64 Engineer's built-in memory benchmarks. Our thanks to FinalWire for providing us with this indispensable tool.
Equalize memory speeds between Ryzen CPUs and Intel's Skylake and Kaby Lake CPUs, and some interesting results fall out. The Ryzen 5 and Ryzen 7 chips enjoy a lead over the Intel quad-cores in memory reads, a smaller lead in copies, and are more or less equal in writes.
It's not all rosy, though, as Ryzen CPUs have about the same memory bandwidth regardless of the number of cores and threads in the socket. The eight-core, 16-thread Ryzen 7 1800X is splitting roughly the same amount of bandwidth among its cores as the four-core, eight-thread Ryzen 5 1500X is across the board (save for writes). Intel, on the other hand, gives its six-core i7-6800K a massive boost in bandwidth over its mainstream desktop CPUs. We'll have to see how AMD's Ryzen Threadripper platform and its quad-channel memory architecture affect these standings.
Raw memory bandwidth is important, but so is the latency of those accesses. All else being equal, the Ryzen chips lag every Intel CPU in this test by a wide margin. Those higher latencies, combined with the bandwidth pressure exerted by many hungry cores, could have an adverse effect on Ryzen CPUs' performance in memory-intensive operations.
Some quick synthetic math tests
AIDA64 offers a useful set of built-in directed benchmarks for assessing the performance of the various subsystems of a CPU. The PhotoWorxx benchmark uses AVX2 on compatible CPUs, while the FPU Julia and Mandel tests use AVX2 with FMA.
The PhotoWorxx test shows how Intel's superior AVX throughput on Broadwell-E, Skylake, and Kaby Lake chips, can effectively allow the company's quad-core CPUs to match or outpace AMD's six- and eight-core parts. The FPU Julia and Mandel tests further illustrate this deficit, where it takes eight AMD Zen cores to match the Core i7-7700K and the Core i7-6800K. The lesser Ryzens don't have a chance.