The Xbox One: Hardware Analysis & Comparison to PlayStation 4
by Anand Lal Shimpi on May 22, 2013 8:00 AM ESTMemory Subsystem
With the same underlying CPU and GPU architectures, porting games between the two should be much easier than ever before. Making the situation even better is the fact that both systems ship with 8GB of total system memory and Blu-ray disc support. Game developers can look forward to the same amount of storage per disc, and relatively similar amounts of storage in main memory. That’s the good news.
The bad news is the two wildly different approaches to memory subsystems. Sony’s approach with the PS4 SoC was to use a 256-bit wide GDDR5 memory interface running somewhere around a 5.5GHz datarate, delivering peak memory bandwidth of 176GB/s. That’s roughly the amount of memory bandwidth we’ve come to expect from a $300 GPU, and great news for the console.
Xbox One Motherboard, courtesy Wired
Die size dictates memory interface width, so the 256-bit interface remains but Microsoft chose to go for DDR3 memory instead. A look at Wired’s excellent high-res teardown photo of the motherboard reveals Micron DDR3-2133 DRAM on board (16 x 16-bit DDR3 devices to be exact). A little math gives us 68.3GB/s of bandwidth to system memory.
To make up for the gap, Microsoft added embedded SRAM on die (not eDRAM, less area efficient but lower latency and doesn't need refreshing). All information points to 32MB of 6T-SRAM, or roughly 1.6 billion transistors for this memory. It’s not immediately clear whether or not this is a true cache or software managed memory. I’d hope for the former but it’s quite possible that it isn’t. At 32MB the ESRAM is more than enough for frame buffer storage, indicating that Microsoft expects developers to use it to offload requests from the system memory bus. Game console makers (Microsoft included) have often used large high speed memories to get around memory bandwidth limitations, so this is no different. Although 32MB doesn’t sound like much, if it is indeed used as a cache (with the frame buffer kept in main memory) it’s actually enough to have a substantial hit rate in current workloads (although there’s not much room for growth).
Vgleaks has a wealth of info, likely supplied from game developers with direct access to Xbox One specs, that looks to be very accurate at this point. According to their data, there’s roughly 50GB/s of bandwidth in each direction to the SoC’s embedded SRAM (102GB/s total bandwidth). The combination of the two plus the CPU-GPU connection at 30GB/s is how Microsoft arrives at its 200GB/s bandwidth figure, although in reality that’s not how any of this works. If it’s used as a cache, the embedded SRAM should significantly cut down on GPU memory bandwidth requests which will give the GPU much more bandwidth than the 256-bit DDR3-2133 memory interface would otherwise imply. Depending on how the eSRAM is managed, it’s very possible that the Xbox One could have comparable effective memory bandwidth to the PlayStation 4. If the eSRAM isn’t managed as a cache however, this all gets much more complicated.
| Microsoft Xbox One vs. Sony PlayStation 4 Memory Subsystem Comparison | ||||||||||||||
| Xbox 360 | Xbox One | PlayStation 4 | ||||||||||||
| Embedded Memory | 10MB eDRAM | 32MB eSRAM | - | |||||||||||
| Embedded Memory Bandwidth | 32GB/s | 102GB/s | - | |||||||||||
| System Memory | 512MB 1400MHz GDDR3 | 8GB 2133MHz DDR3 | 8GB 5500MHz GDDR5 | |||||||||||
| System Memory Bus | 128-bits | 256-bits | 256-bits | |||||||||||
| System Memory Bandwidth | 22.4 GB/s | 68.3 GB/s | 176.0 GB/s | |||||||||||
There are merits to both approaches. Sony has the most present-day-GPU-centric approach to its memory subsystem: give the GPU a wide and fast GDDR5 interface and call it a day. It’s well understood and simple to manage. The downsides? High speed GDDR5 isn’t the most power efficient, and Sony is now married to a more costly memory technology for the life of the PlayStation 4.
Microsoft’s approach leaves some questions about implementation, and is potentially more complex to deal with depending on that implementation. Microsoft specifically called out its 8GB of memory as being “power friendly”, a nod to the lower power operation of DDR3-2133 compared to 5.5GHz GDDR5 used in the PS4. There are also cost benefits. DDR3 is presently cheaper than GDDR5 and that gap should remain over time (although 2133MHz DDR3 is by no means the cheapest available). The 32MB of embedded SRAM is costly, but SRAM scales well with smaller processes. Microsoft probably figures it can significantly cut down the die area of the eSRAM at 20nm and by 14/16nm it shouldn’t be a problem at all.
Even if Microsoft can’t deliver the same effective memory bandwidth as Sony, it also has fewer GPU execution resources - it’s entirely possible that the Xbox One’s memory bandwidth demands will be inherently lower to begin with.
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bji - Wednesday, May 22, 2013 - link
I like the 8 year or longer console cycle. It means that I can focus on enjoying games more than upgrading every couple of years to the latest and greatest that isn't really any more fun to play, just has more eye candy.Hrel - Wednesday, May 22, 2013 - link
"We already have the Windows kernel running on phones, tablets, PCs and the Xbox, now we just need the Xbox OS across all platforms as well." That, 100 infinity BAGILLION times that!I'd actually like to see Nintendo release a console in time for X-mas 2014 with comparable hardware performance. Just because otherwise I don't see how that company will survive and I really don't want Nintendo to go away. I don't know if that's within their realm of possibility but they need to do something because the wiiU is pretty terrible.
tipoo - Wednesday, May 22, 2013 - link
But they won't, as laughable as Wii U sales are that would still anger however many bought that, likely their core base. They'll survive anyways, see their cash reserves, plus any platform Mario and Zelda et al come to will be fine. Nintendo survives on first party, always has.tipoo - Wednesday, May 22, 2013 - link
That said, yes I would have preffered if they just kept motionplus controls and the cost of the tablet controller instead went to an APU.skatendo - Friday, May 24, 2013 - link
Seriously? Have you even tried the GamePad for an extended period of time? The thing is incredible and very useful. Also, the Wii U CPU/GPU is very customized and tailored for gaming. It's smart Nintendo didn't release tech specs because most everybody wouldn't understand how it would perform in real time. Custom silicon is a magnificent thing. Heck look at the 4-core CPU and 12-core GPU for the Tegra 3 and pit that against a paltry looking dual core CPU/GPU Apple A5 and you wouldn't have any competition right? (on paper at least) And who would have thought that the A5 with A FOURTH THE CORES and much slower clockspeed outperformed about twice the game performance the "superior" Tegra 3.marc1000 - Wednesday, May 22, 2013 - link
a great thing MS could do is find a way to put Windows Phone 8 inside of Nvidia Shield - and then have the option to stream your game from the Xbox One to to Shield.That would be awesome, family could be watching TV on the living room and you could have high-quality gaming anywhere - event if it would not be possible to play on the console AND shield at the same time, of course.
Streaming games from X1 to Shield (full control scheme) or any WP8 phone/tablet (simpler games) would be that killer-app that MS needs so badly to boost it's phone business.
nforce4max - Wednesday, May 22, 2013 - link
Interesting read and excited that GCN is being used but the cpu side of things I have to wonder how it will actually perform. Bobcat was fairly weak (think of a Pentium 4) and was terrible starved of memory bandwidth but the worst was that the L2 cache only worked at half the core clock. If the Jaguar cores still have the same sluggish L2 cache then even 8 of them is going to be painful but I suppose devs are going to offload what they can onto the gpu (openCL).As for the 32mb on die memory as stated in the article it all comes down to how it is used. If used for the frame buffer it will limit resolution but make for a huge fps boost as the rop and tmu are bandwidth hogs gpu wise but leave the rest for the cpu and shader. The cpu being weak as it is won't need much provided the gpu doesn't hog to much of the bandwidth. If used as a cache it will make up for the weak L2 cache and provide a unified pool for all 8 cores, if software only then we might have to wait to find out what for.
Overall this is good news for the PC, no more games like GTA4 :D
Arsynic - Wednesday, May 22, 2013 - link
Listening to Sony PR and Sony fanboys you'd think PS4 had every advantage under the sun and will retail for $400.MooseMuffin - Wednesday, May 22, 2013 - link
Nice article Anand. Rare to get level-headed analysis at the start of a console cycle.highend - Wednesday, May 22, 2013 - link
Amiga CDTV in 1990 looked better than XBOX One, see yourself: www.amigahistory.co.uk/cdtv.jpg Also M$ copied from Commodore looks & design