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.

Introduction Memory Subsystem
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  • mczak - Wednesday, May 22, 2013 - link

    Yes exactly, load/store count separately. 2 Int + 2 FP + 2 LS making it 6.
    The more important number is probably dispatch/retire/decode width anyway (which is 2 for all of these).
    Reply
  • nathanddrews - Wednesday, May 22, 2013 - link

    It will be interesting to see how long it takes before XO (or PS4, for that matter) software is running on regular PCs. Reply
  • JPForums - Wednesday, May 22, 2013 - link

    @Anand: "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."

    Agreed, this would be a nice selling point for a future Surface Pro device. It would be a relatively cheap way to bring the added value necessary to justify the higher cost in the eyes of the mass market.
    Reply
  • Arsynic - Wednesday, May 22, 2013 - link

    So the Surface would have to run a hypervisor which would require like 8+ GB of memory if the user wanted a traditional Windows experience along with Xbox games. Reply
  • Spunjji - Wednesday, May 22, 2013 - link

    2 options there:
    1) Dump memory to flash if you *really* feel the need to run both simultaneously at full-tilt (daft)
    2) 16GB RAM, which will cost a whole lot of not much by the time this idea becomes feasible.
    Reply
  • lmcd - Wednesday, May 22, 2013 - link

    Already doesn't cost that much anyway, especially off-die like Surface Pro. Reply
  • RollingCamel - Wednesday, May 22, 2013 - link

    I think that MS is deliberately holding the performance down so tablets and smartphones can quickly catch up and be added to the ecosystem. Reply
  • tipoo - Wednesday, May 22, 2013 - link

    I think it's more so that they can bundle Kinect at a competitive cost. Reply
  • Spunjji - Wednesday, May 22, 2013 - link

    Bit of both, plus being burned by high-spec high-heat parts last gen? Reply
  • tipoo - Wednesday, May 22, 2013 - link

    Why would they want tablets and smartphones to take away their viable market? Reply

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