Who doesn’t love the smell of CPU leaks early in the week? I know I do! Over the weekend, AMD’s slides from their 12 May shareholder presentation were examined more closely by enthusiasts on the SemiAccurate forums. One slide in particular held some details about AMD’s upcoming Zen processor architecture, but it wasn’t what the slide’s text said that was interesting, but rather that die shot to the lower left corner of the image. Eagle-eyed AMD fans will know that AMD currently does not have any CPU on the market that has a makeup that looks like those in the die shot.
The only logical answer is that it’s a photograph of a bunch of Zen dies freshly cut from the wafer, and seeing these for the first time cements a lot of rumors that have leaked on the internet recently. Firstly, it more or less confirms that AMD’s upcoming AM4 socket will be a redesign and won’t be compatible with their existing chips. The CPU die in the shot is rectangular, while previous designs based on Piledriver and Steamroller are square-shaped. This has an effect on the pin count of the processor package, and it’s still unknown at this point if Zen will use an LGA or PGA design.
In her presentation to shareholders and prospective investors, CEO Lisa Su also confirmed some important milestones, namely that Zen chips are being seeded to partners for testing and product development, and that they expect to start making revenue from Zen in 2017. That timeframe is quite small, and it means that AMD intends to release Zen as soon as possible, and possibly even before the end of the year. Su appears to contradict herself later by saying that Zen will launch in 2017 for servers, but this is a separate launch from the consumer side of things.
So what’s in the Zen cores pictured on the left? Users on the SemiAccurate forums promptly tore apart the tiny image in the slide above, and managed to extract higher-resolution copies of the picture for analysis. Take it with all the salt you have in your kitchen, as one should with rumors like these.
The design is pretty interesting, starting with what looks like two quad-core units on a shared die. AMD has used that design before in the Xbox One and PlayStation 4 APUs, which is made up of two quad-core Jaguar units with their own cache allocations and separate memory controllers.
Alongside the processor units are some unknown parts of the CPU that AMD has yet to detail, but looking at some older designs, as well as some input from other journalists in the thread on the SemiAccurate forums, has yielded the labeled die shot that you see on the left. To the bottom left and top right corners are what could be DDR4 memory controllers, which means we’ll see a much-needed boost in memory bandwidth over DDR3. The large oddly shaped area on the bottom right could be the South Bridge, which would make Zen a full system-on-chip (SoC) socketed design, something that AMD started toying with when they launched the AM1 platform.
The top left corner finally holds something that could be related to AMD’s replacement of their Hypertransport interconnect. AMD currently owns the Freedom Fabric interconnect technology, just a piece of the masses of IP they gained when buying out SeaMicro in 2012. Freedom Fabric is very fast, and basically mimics a ring network between connected CPUs in the same way that NVIDIA’s NVLINK technology provides a ring network for their Tesla P100 GPUs to communicate without requiring PCI-Express.
If this is indeed a die shot of Zen (and the evidence definitely slides towards it being true), then that means that this leaked slide from AMD’s financial analyst day is probably accurate:
Here we have what looks like the same layout as the cores seen in the die shot above, but arranged logically. Four cores, 512KB of L2 cache per core, and a shared L3 cache that is fully inclusive matches what’s in the die shot as well. The only data points that have to be ironed out at this stage is how AMD plans to combine multiple units together. It may be the case that two Zen designs are rolled out in late 2016 or early 2017 – one would be the one pictured above, with two Zen units and 16MB of L3 cache, and the other a quad-core Zen CPU with one disabled unit due to defects in the other cores that prevent it from being a fully unlocked product.
The other could be a server CPU with many more Zen units and ungodly amounts of DDR4 memory bandwidth. One of AMD’s hardware partners, CERN (yes, those crazy people with the Large Hadron Collider), leaked specs for a Zen server CPU last year, promising up to 32 cores, 64MB of L3 cache and up to 204GB/s of memory bandwidth. It’s still unclear if that’s an actual product, but based on this slide from AMD’s current product roadmaps, it’s probably real.
AMD is currently preparing to host a livestream event before Computex 2016, on 31 May 2016, detailing their Polaris architecture and the forthcoming socket AM4 Bristol Ridge APUs and the new desktop and mobile chips that derive from the Carrizo family. I’ll have more for you then regarding Zen news, and hopefully we get a launch date out of AMD as well.