Xbox 360 CPU: hype or reality?

[pigdos]

When I read the Xbox 360 official, marketeering garbage it makes their CPU
seem like a supercomputer. I know it's based on the PowerPC architecture,
but which generation of the PowerPC architecture? How does it compare to the
latest Intel/AMD CPU's?
Does each 360 core have all the features of 6th generation (or is it 7th
generation) CPU's (for example, branch prediction, out-of-order execution,
speculative execution)? Does the 360 have a 64-bit data path or 128-bit? I
have looked for this kind of information, but found nothing but Microsoft
hype/marketeering.

 

[Del Cecchi]

When I read the Xbox 360 official, marketeering garbage it makes their CPU
seem like a supercomputer. I know it's based on the PowerPC architecture,
but which generation of the PowerPC architecture? How does it compare to the
latest Intel/AMD CPU's?
Does each 360 core have all the features of 6th generation (or is it 7th
generation) CPU's (for example, branch prediction, out-of-order execution,
speculative execution)? Does the 360 have a 64-bit data path or 128-bit? I
have looked for this kind of information, but found nothing but Microsoft
hype/marketeering.

Why do you want to know? What would you do with the information if you
had it? Why does it matter to you? Just buy your 400 dollar bundle and
kill some zombies.

 

[daytripper]

Why do you want to know? What would you do with the information if you
had it? Why does it matter to you? Just buy your 400 dollar bundle and
kill some zombies.

Someone's having a bad hair day....

 

[YKhan]

When I read the Xbox 360 official, marketeering garbage it makes their CPU
seem like a supercomputer. I know it's based on the PowerPC architecture,
but which generation of the PowerPC architecture? How does it compare to the
latest Intel/AMD CPU's?

From what I've read about it in the past, it's a version of the core

that they used inside the last generation of PPC Macintoshes, the G5.
It has 3 of those cores, but probably a smaller cache than the G5 did.
Those are just what I read in the past, and no I don't have any links
for it.

Yousuf Khan

 

[pigdos]

Yousuf, I've also heard that the Xbox360 CPU lacks branch prediction and
speculative execution. Is this true? It's obvious Microsoft is deliberately
keeping everyone in the dark about the exact specs on this processor.
Probably because they don't want anyone to know how feeble it really is.

I beleive I saw benchmarks last year (SpecINT, SpecFP) of various Athlon 64
systems that beat out the G5's.

 

[Del Cecchi]

that they used inside the last generation of PPC Macintoshes, the G5.
It has 3 of those cores, but probably a smaller cache than the G5 did.
Those are just what I read in the past, and no I don't have any links
for it.

Yousuf Khan

Sigh. Those who know aren't talking and those who talk don't know. At
least pigdos didn't crosspost all over the place.

 

[krw]

Someone's having a bad hair day....

Anyone with the moniker of "pigdos" must be.

 

[krw]

that they used inside the last generation of PPC Macintoshes, the G5.
It has 3 of those cores, but probably a smaller cache than the G5 did.
Those are just what I read in the past, and no I don't have any links
for it.

Bzzzt! Wrong answer. Here is your consolation prize...

 

[David Kanter]

Try using Google. There's easily two or three articles describing the
CPU.

DK

 

[Tony Hill]

When I read the Xbox 360 official, marketeering garbage it makes their CPU
seem like a supercomputer. I know it's based on the PowerPC architecture,
but which generation of the PowerPC architecture?

The XBox 360 uses a triple-core chip where each core is pretty similar
to the one PPE of the Cell processor. It definitely does *not* appear
to be based off the PowerPC 970 (aka the "G5" when in the Steve Jobs
Reality Distortion Field), or the Power5, or really any other current
processor. It bears more resemblance to an old PowerPC 750 (aka
"G3"), though chances are that the chip was for the most part a new
design.

How does it compare to the latest Intel/AMD CPU's?

It's quite a simple design when compared to the latest and greatest
from AMD and Intel. However it does have 3 cores on a single die and
it runs at 3.2GHz, which helps make up for the lack of some features.
It is also an SMT capable (aka "Hyperthreading" in Intel-speak), so
the chip can handle up to 6 simultaneous threads.

Does each 360 core have all the features of 6th generation (or is it 7th
generation) CPU's (for example, branch prediction, out-of-order execution,
speculative execution)?

You can find some info here:

http://arstechnica.com/articles/paedia/cpu/xbox360-2.ars

and here:

http://en.wikipedia.org/wiki/Xenon_(processor)

Beyond that, I don't know much more. The chip does have branch
prediction but not out-of-order execution or speculative execution.

Does the 360 have a 64-bit data path or 128-bit? I

??? I'm not really sure what you mean here. Are you asking about the
path to L2 cache, memory or I/O? The path to L2 cache is 256-bit and
1.6GHz, memory is 256-bit and 1.6GT/s (800MHz DDR I believe, though it
might be 400MHz QDR).

The memory bandwidth is probably the biggest strength of this chip for
the sorts of applications it's likely to run. Combine that with it's
VMX vector units and it can crunch a lot of numbers if they're all
lined up right. The chip probably wouldn't be too hot as a general
purpose CPU, but within the limited scope of a game console chip and
of course the fixed-hardware and development environment of the whole
thing it probably works out pretty well.

 

[YKhan]

Yousuf, I've also heard that the Xbox360 CPU lacks branch prediction and
speculative execution. Is this true? It's obvious Microsoft is deliberately
keeping everyone in the dark about the exact specs on this processor.
Probably because they don't want anyone to know how feeble it really is.

I don't know, but I would assume that it would actually cost them extra
R&D money to remove the branch prediction stuff, so it's not likely.

I beleive I saw benchmarks last year (SpecINT, SpecFP) of various Athlon 64
systems that beat out the G5's.

Might be due to the fact it uses a smaller L2 cache (1MB shared between
the three cores).

Yousuf Khan

 

[nobody]

When I read the Xbox 360 official, marketeering garbage it makes their CPU
seem like a supercomputer. I know it's based on the PowerPC architecture,
but which generation of the PowerPC architecture? How does it compare to the
latest Intel/AMD CPU's?
Does each 360 core have all the features of 6th generation (or is it 7th
generation) CPU's (for example, branch prediction, out-of-order execution,
speculative execution)? Does the 360 have a 64-bit data path or 128-bit? I
have looked for this kind of information, but found nothing but Microsoft
hype/marketeering.

No matter what it is you'll never be able to use it for anything but
xbox, and that one for nothing else but running whatever is sold for
it. You won't be able to boot Windows on it unless Bill Gates orders
his guys to recompile WinXP/Vista for xbox - the hell will freeze over
sooner. Maybe some hacks will figure out how to boot Linux on it -
but with PC prices plummeting why would anyone need it?

NNN

 

[krw]

I don't know, but I would assume that it would actually cost them extra
R&D money to remove the branch prediction stuff, so it's not likely.

No it wouldn't. A couple of fuses or register bits, a small amount
of logic, and you're all set. These sorts of things are normal (to
disable features during chip bringup).

Might be due to the fact it uses a smaller L2 cache (1MB shared between
the three cores).

Um, the "G5" (PPC-970MP) doesn't have three cores, nor a shared
cache. There are two cores, each with a 1MB L2.

 

[Tony Hill]

In case anyone wants some more info, I came across this IBM page
describing the XBox360 CPU:

http://www-128.ibm.com/developerworks/power/library/pa-fpfxbox/?ca=dgr-lnxw09XBoxDesign

It's quite a good overview with a reasonable amount of technical
details and very little marketing fluff.

 

[pigdos]

Yeah, two or three marketing "specification" articles, which are nothing but
MS propaganda.

 

[pigdos]

Thanks Tony, this is exactly the kind of information I was looking for and
couldn't find.

 

[pigdos]

Didn't yhou just say the 360 had two cores? Sigh, I guess you get the booby
prize as well then...

 

[David Kanter]

Didn't yhou just say the 360 had two cores? Sigh, I guess you get the booby
prize as well then...

Try and read what Keith said. He clearly indicated that the latest
MPUs for the G5s are dual core, with 1MB cache each. Notice how this
is different (i.e. not the same as) the MPU in the Xbox360.

Considering that Keith actually works at IBM, there's a pretty good
chance he has just a little bit more insight into the MPU that you
might.

There was a presentation at the Fall Processor Forum on the Xbox360.
Using Google will help, I guarantee. If I can find it, so can you...

DK

 

[Del Cecchi]

Try and read what Keith said. He clearly indicated that the latest
MPUs for the G5s are dual core, with 1MB cache each. Notice how this
is different (i.e. not the same as) the MPU in the Xbox360.

Considering that Keith actually works at IBM, there's a pretty good
chance he has just a little bit more insight into the MPU that you
might.

There was a presentation at the Fall Processor Forum on the Xbox360.
Using Google will help, I guarantee. If I can find it, so can you...

DK

I also believe there is a process technology difference as well.