AMD gives us our first real moment of Zen


Pitting Summit Ridge against Broadwell-E
— 8:00 AM on August 18, 2016

Who would have expected AMD to reveal the most exciting bit of news for the PC enthusiast at the Intel Developer Forum? Last night, the company invited a small group of journalists and analysts to the St. Regis Hotel in San Francisco to give us our first detailed taste of its upcoming Zen CPU architecture.

Zen is a make-or-break moment for AMD. The last high-performance, clean-sheet x86 CPU design from the company was the troubled Bulldozer "module" in the FX-8150, followed up by the Piledriver refinement of that design in 2012's FX-8350. Those chips trailed their Intel contemporaries when they were new, and they've soldiered on in AMD's model lineup for an eternity while Intel has delivered continuous (if slowing) performance improvements and process advancements with its Haswell, Broadwell, and Skylake CPUs. AMD has been continuously refining its APUs in the intervening time, to be sure, but those products have never captured the enthusiast PC builder's imagination in the same way that a Core i7-4790K or Core i7-6700K does.

AMD CEO Lisa Su says the company wants to make high-performance CPUs as much as we want to see them, and the first Zen consumer part, Summit Ridge, may be just the thing to quench our thirst. Summit Ridge is an unabashedly high-end desktop chip fabricated on GlobalFoundries' 14-nm FinFET process, the same as the recently-released Polaris graphics card family. It'll have eight cores and sixteen threads, courtesy of simultaneous multi-threading (better known as Hyper-Threading in Intel CPUs). Unlike Bulldozer and Piledriver, architectures that friend-of-TR David Kanter characterizes as favoring throughput at the expense of single-threaded performance, Zen squarely puts the focus back on strong cores with high single-threaded performance.

To make that happen, AMD CTO Mark Papermaster says each Zen core gets a better branch predictor, its own micro-op cache, wider instruction scheduling, and a doubling of floating-point execution resources.

Simultaneous multi-threading also helps "keep the beast fed," as Papermaster puts it. Each Zen CPU will also have 8MB of shared L3 cache, 512K of L2 cache per core, 64K of instruction cache, and 32K data cache to that end, as well.

This admittedly squishy graph suggests a sense of the efficiency progression from Bulldozer to Excavator to Zen. It may be a folly to try and make sense of this graph, but in the context of desktop parts, Excavator only saw a release in the form of the Athlon X4 845, a 65W, quad-core CPU. If AMD really has delivered 40% more IPC than Excavator with Summit Ridge, we could be looking at a significantly cooler-running and power-sipping chip, even in the form of a high-end desktop part.

Summit Ridge will ride in on the AM4 platform that we first learned about at CES this year. AM4 will offer a number of modern features that are missing from the grizzled 990FX platform and friends, like DDR4 RAM support, PCIe 3.0 connectivity, USB 3.1 Gen2 support, and compatibility with NVMe and SATA Express storage.

I would love to dive deeper into Zen, but these are early days, we don't have a lot of details yet, and time is short as I write this. To my admittedly green eyes, AMD has made sensible design decisions to produce the kind of high-performance core that our CPU testing tends to favor in both gaming and traditional workloads.

Nitty-gritty details aside, the real question on everybody's mind is whether AMD met the 40% IPC improvement goal that it's publicly committed to over the past few months. To make the point that it has, AMD put a Summit Ridge engineering sample running at 3GHz up against an eight-core, sixteen-thread Core i7-6900K artificially limited to the same 3GHz speed. AMD ran the same Blender 3D rendering workload on both chips at the same time. Watch the video above for a sense of how Summit Ridge stacks up to Broadwell-E.

While it's worth remembering that this is only one data point, the Zen chip kept pace with or slightly beat the Broadwell-E CPU in that test. If that performance level holds across a range of workloads, AMD appears to have made some of the large strides it needs to make toward closing the performance gap with Intel CPUs. Tantalizingly, AMD says the 3GHz figure isn't the final clock speed it expects production Zen chips to top out at, either. Final clock speeds for Zen, along with TDP figures and pricing, are still under wraps, but we should learn more as we draw closer to the Summit Ridge launch in the first quarter of 2017.

Zen isn't just coming to enthusiast desktops. AMD wants to regain lost ground in the data center, as well, and its Naples SoC will spearhead that effort. Naples is a 32-core, 64-thread server SoC, and AMD demonstrated a dual-socket server platform with a pair of these chips running Windows Server at the event. AMD expects that Naples will begin showing up in servers in the second quarter of 2017. AMD is also confident that Zen can scale to mobile and embedded devices, all on the same 14-nm GloFo process. We'll begin learning more about Zen-powered APUs and embedded parts in the second half of 2017.

Even with this brief glimpse of Zen, it seems like AMD is starting to turn a corner. The Polaris graphics card lineup may not offer world-beating performance, but it does offer compelling values for the PC gamer, and sales of those products appear to be strong. If the company can deliver a similarly "good enough" high-end desktop CPU family with Zen and Bristol Ridge, it may be well on its way back to health. We'll have to see what the next six months bring, but I see plenty of reason to be cautiously optimistic about AMD's future, and that's a welcome change of pace.

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Tags: CPUs