AMD’s new Zen microprocessor has been a long time coming. We’ve had a few glimpses of what to expect over the past six months, but at the recent AMD Tech Summit, AMD finally revealed the official name for the new processor: Ryzen. It’s an homage to the Zen codename, and probably a hell of a lot easier to trademark than Zen would have been. To be clear, Zen is still the name of the architecture, so I’ll use that when referring to the entire family, while Ryzen specifically refers to the consumer models of the Zen family.
But that’s just the chip name, and we still don’t have an official word on the various models, or precise details of when Ryzen will launch, other than Q1’17. I’ve previously discussed what we know and expect of Zen, but with the new information and additional demonstrations (including AMD’s New Horizon livestream event showcasing Ryzen and even a Vega demonstration), some things are clearer than before—and thankfully, performance is still basically on target.
I’ve updated and overhauled our Zen need-to-know fact sheet, which has now become the Ryzen article you see here. Here’s the brief summary of the latest updates:
- New consumer name for Zen is Ryzen
- 8-core/16-thread parts will clock at 3.4GHz or higher
- TDP for the 8C/16T parts is 95W
- Ryzen equal or better than i7-6900K in multiple tests
- SenseMI and automatic overclocking with improved cooling
- Zen should be much more scalable (e.g., 32-core Naples)
- AMD has Vega GPUs up and running in a Ryzen system
We’ve had variations of AMD’s Bulldozer (Piledriver, Steamroller, and Excavator) for five years, all built using the same building block of a CMT (clustered multi-threading) module that consists of two integer cores with a shared floating-point unit. (It’s technically two 128-bit FMAC units that can also work as a single 256-bit FP unit.) All of that changes with Zen.
From a high level, Zen looks a lot like Intel’s Core architecture. Gone is the CMT module and in its place AMD is using a 4-core/8-thread SMT (symmetric multi-threading) building block. AMD will likely scale down to a 2-core/4-thread module as well, but all indications are that the CPU-only variants of Ryzen will launch with 8C/16T, with a 4C/8T version likely to follow (though no clear indication on how soon that might be).
Current rumors are that the 4C/8T parts will be sold under the SR5 brand, with 8C/16T selling as SR7, and a lower-tier SR3 to follow. Those may be code names or they may end up being retail names (similar to Intel’s i3/i5/i7 nomenclature), but for now I’ll stick with calling the SR7 part 8C/16T and the SR5 part 4C/8T.
Along with SMT support, the pipeline and various other elements of the architecture have also been reworked. The L1 cache is a faster write-back design, and L2 cache is also up to twice the bandwidth. L3 cache meanwhile will deliver up to five times the bandwidth. There’s a new micro-op cache, and each core can issue up to six micro-ops (or four fp-ops) per cycle—similar to Skylake’s 6-wide issue width and 50 percent higher than the 4-wide design of the Bulldozer ‘heavy equipment’ family of CPUs.
Zen has an improved ‘perceptron’ branch prediction algorithm, now decoupled from the fetch stage, which again helps performance. We don’t actually know the pipeline length for Zen (Bulldozer is estimated at a 20-stage pipeline), but better branch prediction can help mitigate having more stages. Notice for example that Intel’s NetBurst pipeline was nominally a 20-stage design, which was ‘too long’ back in the day, and yet all of Intel’s designs going back at least to Sandy Bridge are around the same length. And not to downplay these aspects, but Zen also features larger load, store, and retire buffers, along with improved clock gating.
Then there’s the platform. Ryzen will use a new AM4 socket, with one of several chipsets, A320, B350, and X370. Regardless of chipset, the platform will remain as a dual-channel DDR4 setup, and the CPU socket has 1331 pins. Sticking with dual-channel makes sense as well, as it keeps motherboard costs in check, and it allows for up to 64GB max memory. As for the socket, 1331 is a good number of pins because it’s more than Intel’s LGA1151, and gives sufficient pins for the rumored 36 PCIe Gen3 lanes on the CPU—that would be 32 lanes for graphics cards, with another four lanes likely used to connect with the chipset. However, some previously leaked information indicates X370 will be required for SLI/CF setups, so we could end up with more PCIe lanes linked to the chipset, which would in turn connect to the PCIe slots.
Along with DDR4 support, perhaps equally important is the inclusion of USB 3.1 Gen2 (10Gbps) and NVMe M.2 support. (SATA Express on the other hand appears to be dying fast, so its inclusion doesn’t really matter to me.) Obviously M.2 NVMe drives remain something of a high-end option for most PC builds, and for gaming in particular there’s little benefit compared to a good SATA drive. But then, Ryzen clearly isn’t targeting budget builds as the only option, so being able to use a modern M.2 NVMe drive is a must.
I can’t emphasize enough how big of a fundamental change all of this represents, and it means everything we know about AMD’s CPU performance from the past may no longer apply. AMD has stated a performance target of 40 percent better IPC (Instructions Per Clock) with Zen versus Excavator, and these architecture changes should provide some excellent per-clock performance improvements. A 3.0GHz Zen core should be 40 percent faster than a 3.0GHz Excavator core (though we never saw these outside of APUs), based on AMD’s claims. But there’s a catch: we don’t know the final clock speeds for Zen/Ryzen. I’ll get back to that in a moment, but first let’s talk about some other aspects of the architecture as well as the process technology.