Semiaccurate: Xbox One CPU from 1.6GHz to 1.9GHz.

#1 Edited by AlexGlass (688 posts) -

I don't normally like posting speculations and rumors, but I like the semiaccurate website and forums and this rumor has popped up a number of occasions that the CPU would turn out to be higher than 1.6Ghz closer to 2. It's a great article overall.

As you can see there is a lot on this chip, 8 AMD Jaguar cores organized in to two blocks of four each with a 2MB 16-way L2 cache shared among all associated CPUs. As you might expect the two L2s are coherent but not directly addressable by CPUs in the other group of four. Each Jaguar core has 32K of 2-way L1 I$ and 32K of 8-way L1 D$ as well. AMD’s Jaguar only goes up to four cores so Microsoft had to come up with a mechanism to both ensure coherency among the two clusters of four CPUs and the rest of the system including the GPUs. This is where a lot of what Microsoft added to the system came in.

The most notable change here was that the data paths between the CPUs and the North Bridge/system fabric were massively beefed up. The blue arrows above are for coherent memory accesses, yellow for non-coherent traffic and all the major blocks are coherent with each other. If you think about the sheer volume of coherency data that needs to go between the two CPU blocks, Microsoft probably had to beef up the L2 to NB links to almost match that of the L1 to L2 links. While specifics were not given out, SemiAccurate was told it was “significantly wider” along with beefed up buffers and deeper queues. Don’t discount this as a minor change, it is both critical to the system performance and a very complex thing to do. It will be interesting to see how Sony did their variant if they ever give a talk on the PS4 architecture.

Main Memory Speeds, Feeds, and Coherency:

The CPUs connect to four 64b wide 2GB DDR3-2133 channels for a grand total of 68GB/sec bandwidth. Do note that this number exactly matches the width of a single on-die memory block. One interesting thing to note is that the speed of the CPU MMU’s coherent link to the DRAM controller is only 30GBps, something that strongly suggests that Microsoft sticks with Jaguar’s half-clock speed NB. If the NB to DRAM controller is 256b/32B wide, that would mean it runs at about 938MHz, 1.88GHz if it is 128b/16B wide.

SemiAccurate would be very surprised if it was 128b wide, wires are cheap, power saving areas not. Why is this important? Unless Microsoft’s XBox One architects are masochists that enjoy doing needless and annoying work they would not have reinvented the wheel and put an arbitrarily clockable asynchronous interface between the NB and the CPU cores/L2s. Added complexity, lowered performance, and die penalty for absolutely no useful upside is not a good architectural decision. That means the XBox One’s 8 Jaguar cores are clocked at ~1.9GHz, something that wasn’t announced at Hot Chips. Now you know.

The CPU NB also has coherent links to the GPU MMU and I/O MMU, something you would expect on any system that takes GPU compute work seriously. AMD has their HSA/HUMA architecture coming with Kaveri in short order but XBO is based on a design ~1+ generations older so no advanced AMD CPU/GPU coherency here. Luckily Microsoft is on the ball here and put their own mechanism in which they would unfortunately not go in to detail on. What SemiAccurate has heard about it says they did a pretty impressive job but until it is fully disclosed we can’t comment with authority. Lets just leave things at, “From what we can tell it looks good”.

Another thing to notice is a rather odd direct and coherent path between the AV In block in the GPU/accelerator area to the Audio DMA unit in the I/O area. The Audio DMA unit also has a direct link to the Audio Out/Resize/Composting block, both of these are one way. Since one is an inbound unit and the other is an outbound unit that kind of makes sense, if there is need to go the other way the two can talk via the CPU MMU. While this may not make much sense on the surface, much of the XBO’s audio functionality is devoted to processing the Kinect’s data stream so high bandwidth and low latency are kind of necessary. More on this later.S|A

Note: This is the first part and only covers part of the system. More including the GPU, embedded memory, and audio systems to come.

#2 Edited by Blu3V3nom07 (4235 posts) -

Oh okay, cool.

So That's what meant SA meant. Didn't know. But then, what does D$ mean?

#3 Posted by AlexGlass (688 posts) -

Oh okay, cool.

So That's what meant SA meant. Didn't know. But then, what does D$ mean?

15% more instructions per cycle. More physics. More AI. More CPU calculation per second. Than before.

Zombies will now talk back in Dead Rising 3. Just not in Portuguese ;)

#4 Edited by SongWriter1987 (134 posts) -

Wait, isn't the xbox 360 cpu clocked at 3.0 ghz? I guess the low clock speed is to cut down on overheating. But still, wow.

My PC cpu is clocked at 4.5 ghz. lol. Great next gen hardware, Sony/MS

#5 Posted by Krakn3Dfx (2499 posts) -

According to a few people on other sites who know more than I do, the math doesn't really add up. Also, considering they made such a big deal about a 53Mhz GPU increase, going to say it would be weird if they bumped their CPU up from 1.6Ghz to 1.9Ghz and didn't say anything about it.

I guess we'll see, but seems like idle speculation at this point.

#6 Edited by AlexGlass (688 posts) -

According to a few people on other sites who know more than I do, the math doesn't really add up. Also, considering they made such a big deal about a 53Mhz GPU increase, going to say it would be weird if they bumped their CPU up from 1.6Ghz to 1.9Ghz and didn't say anything about it.

I guess we'll see, but seems like idle speculation at this point.

I don't believe MS confirmed the speed of the CPU did they? I was under the impression that 1.6Ghz came from vgleaks.

#7 Posted by Korwin (2893 posts) -

Wait, isn't the xbox 360 cpu clocked at 3.0 ghz? I guess the low clock speed is to cut down on overheating. But still, wow.

My PC cpu is clocked at 4.5 ghz. lol. Great next gen hardware, Sony/MS

Clock speed isn't a relevant measure of performance between architectures.

#8 Edited by SongWriter1987 (134 posts) -

@korwin: Sure, clock speed is totally irrelevant, I mean no one overclocks anymore because there is no correlation between clock speed and performance.

#9 Edited by Kidavenger (3582 posts) -

I don't normally like posting speculations and rumors,

Sure thing...

#10 Posted by Pr1mus (3951 posts) -

Wait, isn't the xbox 360 cpu clocked at 3.0 ghz? I guess the low clock speed is to cut down on overheating. But still, wow.

My PC cpu is clocked at 4.5 ghz. lol. Great next gen hardware, Sony/MS

You don't understand how hardware works.

#11 Posted by Zelyre (1224 posts) -

@korwin: Sure, clock speed is totally irrelevant, I mean no one overclocks anymore because there is no correlation between clock speed and performance.

When dealing with two different architectures, clock speed is not the end all, be all metric. The Pentium 4's architecture allowed it to ramp up its clock speeds much higher than AMD's Athlon's. However, the much longer pipeline made the P4 a dog compared to the Athlon.

It's why a 1.6 ghz i5 is is going to utterly thrash a P4 at 4ghz. A 2ghz ARM processor isn't going to touch the raw performance of a 800mhz P3. Nor will a 1.8ghz Atom perform as well as a 1ghz Athlon, despite them both being x86.

#12 Posted by SpoogeMcduck (191 posts) -

"Too much graphics!"

#13 Posted by Korwin (2893 posts) -

@korwin: Sure, clock speed is totally irrelevant, I mean no one overclocks anymore because there is no correlation between clock speed and performance.

Between identical architectures (Haswell to Haswell) yes, between 2 architectures as radically different as lower power x86_64 (Jaguar is for light weight computing in the same vein as Atom) and 8 year old IBM PowerPC it's completely irrelevant.

#14 Edited by Korwin (2893 posts) -
#15 Edited by TheHBK (5507 posts) -

Wait, isn't the xbox 360 cpu clocked at 3.0 ghz? I guess the low clock speed is to cut down on overheating. But still, wow.

My PC cpu is clocked at 4.5 ghz. lol. Great next gen hardware, Sony/MS

Yeah but architecture and # of transistors and cores is everything. I had a Pentium 4 at 3.0ghz in my old computer but a core duo at 1.7 ghz would whip its ass. The 360 cpu is 3 cores at 3 GHz. Also that is PowerPC based, now x86. Point being, the Xbox one and PS4 CPUs are 8-core Jaguars. Jaguars are cool. They are much better CPUs.

#16 Edited by OurSin_360 (937 posts) -

Honestly, i'm concerned if they are still testing clock speeds this late in development. I hope they don't repeat the overheating issues again

#17 Edited by TruthTellah (9321 posts) -

Honestly, i'm concerned if they are still testing clock speeds this late in development. I hope they don't repeat the overheating issues again

Well, it's an understandable development. The initially reported clock speed was an estimate of the final box's capability, but after finishing the production model, they realized it could handle more. Basically, they had over-compensated for potential overheating issues, and that allowed them to increase the clock a little bit. Fortunately, they seem pretty aware of the issues in the past, and the console will be able to manage its performance in case of excessive heat. We'll have to see how it really works out in practice, but it seems rather promising.

#18 Edited by Korwin (2893 posts) -

Honestly, i'm concerned if they are still testing clock speeds this late in development. I hope they don't repeat the overheating issues again

Eh the chip doesn't suck enough juice down to generate a whole lot of heat, they would have to mess up in a big way to cool that thing poorly.

#19 Posted by The_Laughing_Man (13629 posts) -

Wait so are they saying there is more in there that MS has not talked about?

#20 Posted by Brendan (7844 posts) -
#21 Posted by The_Laughing_Man (13629 posts) -
#23 Edited by EXTomar (4843 posts) -

I was thinking more of that this changes things from just plain old Bass-o-matic to Super Bass-o-matic.

ps. "I don't normally like posting speculations and rumors..." must be a pretty funny thing for him to write.

#24 Posted by The_Laughing_Man (13629 posts) -

@extomar said:

I was thinking more of that this changes things from just plain old Bass-o-matic to Super Bass-o-matic.

ps. "I don't normally like posting speculations and rumors..." must be a pretty funny thing for him to write.

There is my gift to you all. Have a nice laugh.

http://www.ign.com/boards/threads/xbox-one-dgpu.453311803/

#25 Posted by Syed117 (392 posts) -

The entire lead up to the release of these consoles has been ridiculous.

One rumor after another. Most of them based on speculation from neogaf.

Just want the boxes to get here so we can see what exactly is inside.

#26 Edited by EXTomar (4843 posts) -

I can't handle the amount of truthiness in that thread! The power is so much they can't tell us, the people who might buy it, about it. Why? Because it will frighten small children and dogs if they knew the truth.

#27 Posted by The_Laughing_Man (13629 posts) -

@extomar said:

I can't handle the amount of truthiness in that thread! The power is so much they can't tell us, the people who might buy it, about it. Why? Because it will frighten us.

Go read the live journal stuff.

#28 Posted by Amafi (877 posts) -

@extomar said:

I can't handle the amount of truthiness in that thread! The power is so much they can't tell us, the people who might buy it, about it. Why? Because it will frighten small children and dogs if they knew the truth.

Shit reminds me of reading David Icke's forums, just slightly less scary.

#30 Posted by AlexGlass (688 posts) -

Wait so are they saying there is more in there that MS has not talked about?

I think they were just referring to the customized huma-like architecture which MS hasn't fully detailed. They had to modify the chip, because the original architecture didn't support it.

Honestly, i'm concerned if they are still testing clock speeds this late in development. I hope they don't repeat the overheating issues again

Anything that might change now is likely to have been tested for months in advance but I'm betting it's more that the original vgleak specs which are now more than 2 years old were slightly off. Which is where I believe the 1.6GHz number came from. Overheating is highly unlikely with that box and that fan. Looks to me like they went overboard to make sure that doesn't happen because that's the biggest fan I have ever seen in a case that small. Freaking thing takes up 25% of the console.

No subtly about their intentions there at all.

#31 Posted by Nekroskop (2786 posts) -

I can't think of anyone I know that wants that thing. The downfall is going to be glorious.

#32 Posted by Nhoj_Sllew (179 posts) -

I can't think of anyone I know that wants that thing. The downfall is going to be glorious.

cool thanks for stopping by

#33 Posted by Hunter5024 (5815 posts) -

Ooh OOH! I actually ordered my CPU yesterday, can I be a PC elitist yet? I'm gonna try it out. Ahem. Have fun with half as many GHz as me, you poor console peasants.

That felt good. I'm sure it will come more naturally as I buy more parts.

Online
#34 Posted by Nekroskop (2786 posts) -

@nekroskop said:

I can't think of anyone I know that wants that thing. The downfall is going to be glorious.

cool thanks for stopping by

Check out my show at The Ice House in Pasadena the 24th.

#35 Edited by AlexGlass (688 posts) -

Guess they were on to something after all. I knew I liked those semiaccurate guys for a reason. Missed it by1.5GHz, but good call on their part. They were the first to really point to a higher clockspeed with some logic to back it up.

#36 Posted by Humanity (9602 posts) -

@nhoj_sllew said:

@nekroskop said:

I can't think of anyone I know that wants that thing. The downfall is going to be glorious.

cool thanks for stopping by

Check out my show at The Ice House in Pasadena the 24th.

I don't know anyone that likes Pepsi, that company is probably gonna go under pretty soon.

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