Original Link: http://www.anandtech.com/show/6972/xbox-one-hardware-compared-to-playstation-4



It’s that time of decade again. Time for a new Xbox. It took four years for Microsoft to go from the original Xbox to the Xbox 360. The transition from Xbox 360 to the newly announced Xbox One will take right around 8 years, and the 360 won’t be going away anytime soon either. The console business demands long upgrade cycles in order to make early investments in hardware (often sold at a loss) worthwhile. This last round was much longer that it ever should have been, so the Xbox One arrives to a very welcoming crowd.

Yesterday Microsoft finally took the covers off the new Xbox, what it hopes will last for many years to come. At a high level here’s what we’re dealing with:

- 8-core AMD Jaguar CPU
- 12 CU/768 SP AMD GCN GPU
- 8GB DDR3 system memory
- 500GB HDD
- Blu-ray drive
- 2.4/5.0GHz 802.11 a/b/g/n, multiple radios with WiFi Direct support
- 4K HDMI in/out (for cable TV passthrough)
- USB 3.0
- Available later this year

While Microsoft was light on technical details, I believe we have enough to put together some decent analysis. Let’s get to it.

Chassis

The Xbox 360 was crafted during a time that seems so long ago. Consumer electronics styled in white were all the rage, we would be a few years away from the aluminum revolution that engulfs us today. Looking at the Xbox One tells us a lot about how things have changed.

Microsoft isn’t so obsessed with size here, at least initially. Wired reports that the Xbox One is larger than the outgoing 360, although it’s not clear whether we’re talking about the new slim or the original design. Either way, given what’s under the hood - skimping on cooling and ventilation isn’t a good thing.

The squared off design and glossy black chassis scream entertainment center. Microsoft isn’t playing for a position in your games cabinet, the Xbox One is just as much about consuming media as it is about playing games.

In its presentation Microsoft kept referencing how the world has changed. Smartphones, tablets, even internet connectivity are very different today than they were when the Xbox 360 launched in 2005. It’s what Microsoft didn’t mention that really seems to have played a role in its decision making behind the One: many critics didn’t see hope for another generation of high-end game consoles.

With so much of today focused on mobile, free to play and casual gaming on smartphones and tablets - would anyone even buy a next-generation console? For much of the past couple of years I’ve been going around meetings saying that before consolidation comes great expansion. I’ve been saying this about a number of markets, but I believe the phrase is very applicable to gaming. Casual gaming, the advent of free to play and even the current mobile revolution won’t do anything to the demand for high-end consoles today or in the near term - they simply expand the market for gamers. Eventually those types of games and gaming platforms will grow to the point where they start competing with one another and then the big console players might have an issue to worry about, but I suspect that’s still some time away. The depth offered by big gaming titles remains unmatched elsewhere. You can argue that many games are priced too high, but the Halo, BioShock, Mass Effect, CoD experience still drives a considerable portion of the market.

The fact that this debate is happening however has to have impacted Microsoft. Simply building a better Xbox 360 wasn’t going to guarantee success, and I suspect there were not insignificant numbers within the company who felt that even making the Xbox One as much of a gaming machine as it is would be a mistake. What resulted was a subtle pivot in strategy.

The Battle for the TV

Last year you couldn’t throw a stone without hitting a rumor of Apple getting into the TV business. As of yet those rumors haven’t gone anywhere other than to point to continued investment in the Apple TV. Go back even further and Google had its own TV aspirations, although met with far less success. More recently, Intel threw its hat into the ring. I don’t know for sure how things have changed with the new CEO, but as far as I can tell he’s a rational man and things should proceed with Intel Media’s plans for an IPTV service. All of this is a round about way of saying that TV is clearly important and viewed by many as one of the next ecosystem battles in tech.

Combine the fact that TV is important, with the fact that the Xbox 360 has evolved into a Netflix box for many, add a dash of uncertainty for the future of high end gaming consoles and you end up with the formula behind the Xbox One. If the future doesn’t look bright for high-end gaming consoles, turning the Xbox into something much more than that will hopefully guarantee its presence in the living room. At least that’s what I suspect Microsoft’s thinking was going into the Xbox One. With that in mind, everything about the One makes a lot of sense.



CPU & GPU Hardware Analyzed

Although Microsoft did its best to minimize AMD’s role in all of this, the Xbox One features a semi-custom 28nm APU designed with AMD. If this sounds familiar it’s because the strategy is very similar to what Sony employed for the PS4’s silicon.

The phrase semi-custom comes from the fact that AMD is leveraging much of its already developed IP for the SoC. On the CPU front we have two Jaguar compute units, each one with four independent processor cores and a shared 2MB L2 cache. The combination of the two give the Xbox One its 8-core CPU. This is the same basic layout of the PS4‘s SoC.

If you’re not familiar with it, Jaguar is the follow-on to AMD’s Bobcat core - think of it as AMD’s answer to the Intel Atom. Jaguar is a 2-issue OoO architecture, but with roughly 20% higher IPC than Bobcat thanks to a number of tweaks. In ARM terms we’re talking about something that’s faster than a Cortex A15. I expect Jaguar to be close but likely fall behind Intel’s Silvermont, at least at the highest shipping frequencies. Jaguar is the foundation of AMD’s Kabini and Temash APUs, where it will ship first. I’ll have a deeper architectural look at Jaguar later this week. Update: It's live!

Inside the Xbox One, courtesy Wired

There’s no word on clock speed, but Jaguar at 28nm is good for up to 2GHz depending on thermal headroom. Current rumors point to both the PS4 and Xbox One running their Jaguar cores at 1.6GHz, which sounds about right. In terms of TDP, on the CPU side you’re likely looking at 30W with all cores fully loaded.

The move away from PowerPC to 64-bit x86 cores means the One breaks backwards compatibility with all Xbox 360 titles. Microsoft won’t be pursuing any sort of a backwards compatibility strategy, although if a game developer wanted to it could port an older title to the new console. Interestingly enough, the first Xbox was also an x86 design - from a hardware/ISA standpoint the new Xbox One is backwards compatible with its grandfather, although Microsoft would have to enable that as a feature in software - something that’s quite unlikely.

Microsoft Xbox One vs. Sony PlayStation 4 Spec comparison
  Xbox 360 Xbox One PlayStation 4
CPU Cores/Threads 3/6 8/8 8/8
CPU Frequency 3.2GHz 1.6GHz (est) 1.6GHz (est)
CPU µArch IBM PowerPC AMD Jaguar AMD Jaguar
Shared L2 Cache 1MB 2 x 2MB 2 x 2MB
GPU Cores   768 1152
Peak Shader Throughput 0.24 TFLOPS 1.23 TFLOPS 1.84 TFLOPS
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
Manufacturing Process   28nm 28nm

On the graphics side it’s once again obvious that Microsoft and Sony are shopping at the same store as the Xbox One’s SoC integrates an AMD GCN based GPU. Here’s where things start to get a bit controversial. Sony opted for an 18 Compute Unit GCN configuration, totaling 1152 shader processors/cores/ALUs. Microsoft went for a far smaller configuration: 768 (12 CUs).

Microsoft can’t make up the difference in clock speed alone (AMD’s GCN seems to top out around 1GHz on 28nm), and based on current leaks it looks like both MS and Sony are running their GPUs at the same 800MHz clock. The result is a 33% reduction in compute power, from 1.84 TFLOPs in the PS4 to 1.23 TFLOPs in the Xbox One. We’re still talking about over 5x the peak theoretical shader performance of the Xbox 360, likely even more given increases in efficiency thanks to AMD’s scalar GCN architecture (MS quotes up to 8x better GPU performance) - but there’s no escaping the fact that Microsoft has given the Xbox One less GPU hardware than Sony gave the PlayStation 4. Note that unlike the Xbox 360 vs. PS3 era, Sony's hardware advantage here won't need any clever developer work to extract - the architectures are near identical, Sony just has more resources available to use.

Remember all of my talk earlier about a slight pivot in strategy? Microsoft seems to believe that throwing as much power as possible at the next Xbox wasn’t the key to success and its silicon choices reflect that.



Memory 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.



Power & Thermals

Microsoft made a point to focus on the Xbox One’s new power states during its introduction. Remember that when the Xbox 360 was introduced, power gating wasn’t present in any shipping CPU or GPU architectures. The Xbox One (and likely the PlayStation 4) can power gate unused CPU cores. AMD’s GCN architecture supports power gating, so I’d assume that parts of the GPU can be power gated as well. Dynamic frequency/voltage scaling is also supported. The result is that we should see a good dynamic range of power consumption on the Xbox One, compared to the Xbox 360’s more on/off nature.

AMD’s Jaguar is quite power efficient, capable of low single digit idle power so I would expect far lower idle power consumption than even the current slim Xbox 360 (50W would be easy, 20W should be doable for truly idle). Under heavy gaming load I’d expect to see higher power consumption than the current Xbox 360, but still less than the original 2005 Xbox 360.

Compared to the PlayStation 4, Microsoft should have the cooler running console under load. Fewer GPU ALUs and lower power memory don’t help with performance but do at least offer one side benefit.

OS
 

The Xbox One is powered by two independent OSes running on a custom version of Microsoft’s Hyper-V hypervisor. Microsoft made the hypervisor very lightweight, and created hard partitions of system resources for the two OSes that run on top of it: the Xbox OS and the Windows kernel.

The Xbox OS is used to play games, while the Windows kernel effectively handles all apps (as well as things like some of the processing for Kinect inputs). Since both OSes are just VMs on the same hypervisor, they are both running simultaneously all of the time, enabling seamless switching between the two. With much faster hardware and more cores (8 vs 3 in the Xbox 360), Microsoft can likely dedicate Xbox 360-like CPU performance to the Windows kernel while running games without any negative performance impact. Transitioning in/out of a game should be very quick thanks to this architecture. It makes a ton of sense.

Similarly, you can now multitask with apps. Microsoft enabled Windows 8-like multitasking where you can snap an app to one side of the screen while watching a video or playing a game on the other.

The hard partitioning of resources would be nice to know more about. The easiest thing would be to dedicate a Jaguar compute module to each OS, but that might end up being overkill for the Windows kernel and insufficient for some gaming workloads. I suspect ~1GB of system memory ends up being carved off for Windows.

Kinect & New Controller
 

All Xbox One consoles will ship with a bundled Kinect sensor. Game console accessories generally don’t do all that well if they’re optional. Kinect seemed to be the exception to the rule, but Microsoft is very focused on Kinect being a part of the Xbox going forward so integration here makes sense.

The One’s introduction was done entirely via Kinect enabled voice and gesture controls. You can even wake the Xbox One from a sleep state using voice (say “Xbox on”), leveraging Kinect and good power gating at the silicon level. You can use large two-hand pinch and stretch gestures to quickly move in and out of the One’s home screen.

The Kinect sensor itself is one of 5 semi-custom silicon elements in the Xbox One - the other four are: SoC, PCH, Kinect IO chip and Blu-ray DSP (read: the end of optical drive based exploits). In the One’s Kinect implementation Microsoft goes from a 640 x 480 sensor to 1920 x 1080 (I’m assuming 1080p for the depth stream as well). The camera’s field of view was increased by 60%, allowing support for up to 6 recognized skeletons (compared to 2 in the original Kinect). Taller users can now get closer to the camera thanks to the larger FOV, similarly the sensor can be used in smaller rooms.

The Xbox One will also ship with a new redesigned wireless controller with vibrating triggers:

Thanks to Kinect's higher resolution and more sensitive camera, the console should be able to identify who is gaming and automatically pair the user to the controller.

TV
 

The Xbox One features a HDMI input for cable TV passthrough (from a cable box or some other tuner with HDMI out). Content passed through can be viewed with overlays from the Xbox or just as you would if the Xbox wasn’t present. Microsoft built its own electronic program guide that allows you to tune channels by name, not just channel number (e.g. say “Watch HBO”). The implementation looks pretty slick, and should hopefully keep you from having to switch inputs on your TV - the Xbox One should drive everything. Microsoft appears to be doing its best to merge legacy TV with the new world of buying/renting content via Xbox Live. It’s a smart move.

One area where Microsoft is being a bit more aggressive is in its work with the NFL. Microsoft demonstrated fantasy football integration while watching NFL passed through to the Xbox One.



Final Words

It’s nearly impossible for the Xbox One not to be a substantial upgrade over the Xbox 360. The fact that Microsoft could ship a single integrated SoC instead of a multi-chip CPU+GPU solution this generation is telling enough. You don’t need to integrate anywhere near the fastest CPUs and GPUs to outperform the Xbox 360, something closer to the middle of the road works just fine.

Microsoft won’t have any issues delivering many times the performance of the Xbox 360. The Xbox One features far more compute power and memory bandwidth than the Xbox 360. Going to 8GB of RAM is also a welcome upgrade, especially since it’s identical to what Sony will ship on the PlayStation 4. As AMD is supplying relatively similar x86 CPU and GCN GPU IP to both consoles, porting between them (and porting to PCs) should be far easier than ever before. The theoretical performance comparison between the two next-gen consoles is where things get a bit sticky.

Sony gave the PS4 50% more raw shader performance, plain and simple (768 SPs @ 800MHz vs. 1152 SPs & 800MHz). Unlike last generation, you don't need to be some sort of Jedi to extract the PS4's potential here. The Xbox One and PS4 architectures are quite similar, Sony just has more hardware under the hood. We’ll have to wait and see how this hardware delta gets exposed in games over time, but the gap is definitely there. The funny thing about game consoles is that it’s usually the lowest common denominator that determines the bulk of the experience across all platforms.

On the plus side, the Xbox One should enjoy better power/thermal characteristics compared to the PlayStation 4. Even compared to the Xbox 360 we should see improvement in many use cases thanks to modern power management techniques.

Differences in the memory subsytems also gives us some insight into each approach to the next-gen consoles. Microsoft opted for embedded SRAM + DDR3, while Sony went for a very fast GDDR5 memory interface. Sony’s approach (especially when combined with a beefier GPU) is exactly what you’d build if you wanted to give game developers the fastest hardware. Microsoft’s approach on the other hand looks a little more broad. The Xbox One still gives game developers a significant performance boost over the previous generation, but also attempts to widen the audience for the console. It’s a risky strategy for sure, especially given the similarities in the underlying architectures between the Xbox One and PS4. If the market for high-end game consoles has already hit its peak, then Microsoft’s approach is likely the right one from a business standpoint. If the market for dedicated high-end game consoles hasn’t peaked however, Microsoft will have to rely even more on the Kinect experience, TV integration and its exclusive franchises to compete.

Arguably the most interesting thing in all of this is the dual-OS + hypervisor software setup behind the Xbox One. With the Windows kernel running alongside the Xbox OS, I wonder how much of a stretch it would be to one day bring the same setup to PCs. Well before the Xbox One hits the end of its life, mainstream PC APUs will likely be capable of delivering similar performance. Imagine a future Surface tablet capable of doing everything your Xbox One can do. That's really the trump card in all of this. The day Microsoft treats Xbox as a platform and not a console is the day that Apple and Google have a much more formidable competitor. Xbox One at least gets the software architecture in order, then we need PC/mobile hardware to follow suit and finally for Microsoft to come to this realization and actually make it happen. 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.

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