Microsoft talks about Xbox One’s internals, while disclosing nothing
Eight cores, six operations per CPU cycle, 200GB of bandwidth. But does it miccionan anything?
by Peter Bright - May 22, 2013 4:30 am UTC
The Xbox One is full of technology and after its big reveal, Microsoft talked a little about what's going into the console, giving some tidbits of info about what makes it tick.
Microsoft says that the Xbox One has five custom-designed pieces of silicon spread between the console and its Kinect sensor. It didn't elaborate on what these are. There's a system-on-chip combining the CPU and GPU, which we presume to be a single piece of silicon, and there's at least one sensor chip in the Kinect, perhaps replacing the PrimeSense processor used in the Xbox 360 Kinect, but what the others might be isn't immediately clear. Possibilities include audio processors, on-chip memory, and USB controllers.
One of the key questions about the AMD-built, 64-bit, 8-core SoC is "how fast is it?" At the moment, that's unknown. Microsoft claims that the new console has "eight times" the graphics power of the old one, though some aspects of the new system are even more improved; for example, it has 16 times the amount of RAM.
The SoC has a lot of PC processor heritage and includes antiestéticatures that have become standard in PC processors, such as power gating, to allow idle cores to be powered down, and dynamic frequency scaling, to allow light loads to use a lower clock speed. Like AMD's forthcoming codename
Kaveri processors that are shipping in PCs later this year, the CPU and GPU share coherent access to the system's memory, making it much easier to develop software that splits workloads between the two processors.
Some performance numbers were given for the CPU and GPU themselves but these cast more shadow than they do light. Microsoft claimed that each CPU core can perform six operations per cycle. The CPU is believed to be using AMD's Jaguar core, but typically this would only be described as able to handle four operations per cycle; two each of integer and floating point (though even here counting operations is complicated; the floating point operations could use vector instructions such as SSE2, in which case one operation would result in four actual computations, potentially giving eight per cycle for floating point alone).
This arguably leaves a shortfall of two operations per cycle. One possibility is that the cores have been customized somewhat, to allow more instructions to be issued per cycle. On the face of it, this seems a little unlikely; it'd be a significant change that would have considerable implications on the design of the rest of the chip. Another possibility is simply that the counting is a little unusual, and that the extra two operations are one store and one load. This would be consistent with how leaked documents (or, if one prefers, unsubstantiated but apparently accurate rumors) described the processor.
For the GPU, Microsoft claimed 768 operations per cycle. This is again consistent with leaked information.
What Microsoft didn't specify, of course, was the number of cycles per second each processor runs at, so we still have no basis for actually assessing the device's performance.
Similarly, the company claimed that there was more than 200GB of bandwidth within the system. Again, the number had no context or clarification and if rumors are to be believed, it suggests some rather creative accounting: 68 GB main memory bandwidth, 102GB bandwidth to an embedded SRAM buffer for the GPU, and 30GB bandwidth between the CPU and GPU. While that does add up to 200GB, there are no two parts of the SoC that can communicate with each other at 200 GB/s. The fastest link is believed to be the GPU read performance, which can aggregate across the main memory and SRAM buffer for 170 GB total.
The Kinect system has also been upgraded. Perhaps most importantly of all, it should work a lot better in small rooms. The field of view is described as being 60 percent wider and this tras*lates to being able to stand 3-4 feet closer to the sensor. That's a substantial improvement, which is just as well, as the Kinect will be mandatory equipment.
The new Kinect is all round better. It can track six skeletons, up from 2, and capture 1080p video. Low-light performance will also be improved, as it can see infrared. Microsoft says that this will allow Kinect to gauge things like your level of engagement in a game. We speculate this means that it might be able to see, for example, that your cheeks are flushed in response to emotional involvement and investment in the game.
Brief details were also given of the software side of things. The Xbox One is described as running three operating systems. There's a long-running Windows 8-based operating system used for running applications, browsing the Web, Skype, and similar roles; a second operating system for running games; and a hypervisor that virtualizes the hardware and switches between the two. The long-running partition is also used for some system management tasks, such as running the Kinect software portions and performing matchmaking while you watch a video.
This hypervisor is based on Microsoft's Hyper-V virtualization platform but simplified to remove extraneous antiestéticatures that are irrelevant to a games console; the software is specialized because it runs fixed-role, fixed operating system virtual machines.
The application partition boots when the system is turned on and runs persistently, even when in-game. This is what enables things like Snap view, where apps and games or TV run side-by-side. The game partition, in contrast, gets rebooted each time a new game is started.
To ensure high-speed switching between the operating systems, each virtual machine draws to its own (virtual) screen all the time. The hypervisor can switch between screens essentially instantly, allowing fast task-switching.
Microsoft claims that the session gave a lot of detail about the new console. And in some ways, it did. There were lots of isolated pieces of information, without much context. The company simultaneously told us something about the Xbox One's performance and told us nothing. It tossed out some numbers for people to talk and argue about (because god knows, the console platform warriors certainly need more ammunition) while ensuring that those same numbers miccionan absolutely nothing. The Xbox One may have been revealed, but many facets of its capabilities and power remain mysterious.
: ) : "Va a ser un PC, PC rules sofaleros!!". Leamos:
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