Introducing the Xbox 360's Xenon CPU

The Xenon processor was designed from the ground up to be a 3-core CPU, so unlike Cell, there are no disabled cores on the Xenon chip itself in order to improve yield.  The reason for choosing 3 cores is because it provides a good balance between thread execution power and die size.  According to Microsoft's partners, the sweet spot for this generation of consoles will be between 4 and 6 execution threads, which is where the 3-core CPU came from. 

The chip is built on a 90nm process, much like Cell, and will run at 3.2GHz - also like Cell.  All of the cores are identical to one another, and they are very similar to the PPE used in the Cell microprocessor, with a few modifications. 

The focus of Microsoft's additions to the core has been in the expansion of the VMX instruction set.  In particular, Microsoft now includes a single cycle dot-product instruction as a part of the VMX-128 ISA that is implemented on each core.  Microsoft has stated that there is nothing stopping IBM from incorporating this support into other chips, but as of yet we have not seen anyone from the Cell camp claim support for single cycle dot-products on the PPE. 

The three cores share a meager 1MB L2 cache, which should be fine for single threaded games but as developers migrate more to multi-threaded engines, this small cache will definitely become a performance limiter.  With each core being able to execute two threads simultaneously, you effectively have a worst case scenario of 6 threads splitting a 1MB L2 cache.  As a comparison, the current dual core Pentium 4s have a 1MB L2 cache per core and that number is only expected to rise in the future. 

The most important selling point of the Xbox 360's Xenon core is the fact that all three cores are identical, and they are all general purpose microprocessors.  The developer does not have to worry about multi-threading beyond the point of getting their code to be thread safe; once it is multi-threaded, it can easily be run on any of the cores.  The other important thing to keep in mind here is that porting between multi-core PC platforms and the Xbox 360 will be fairly trivial.  Anywhere any inline assembly is used there will obviously have to be changes, but with relatively minor code changes and some time optimizing, code portability between the PC and the Xbox 360 shouldn't be very difficult at all.  For what it is worth, porting game code between the PC and the Xbox 360 will be a lot like Mac developers porting code between Mac OS X for Intel platforms and PowerPC platforms: there's an architecture switch, but the programming model doesn't change much. 

The same cannot however be said for Cell and the PlayStation 3.  The easiest way to port code from the Xbox 360 to the PS3 would be to run the code exclusively on the Cell's single PPE, which obviously wouldn't offer very good performance for heavily multi-threaded titles.  But with a some effort, the PlayStation 3 does have a lot of potential.

The Consoles and their CPUs Xenon vs. Cell
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  • PS3 Masterbater 5 - Tuesday, January 09, 2007 - link

    I WOULD JUST LIKE TO SAY THAT IF PS3 HAD A HOLE IN IT I WOULD INSERT MY PENIS IN AND MAKE SWEET LOVE TO IT BECAUSE IT IS THE GREATEST THING EVER. NINTENDO WII CAN SUCK MY HUGE COCK BECAUSE ITS A LITTLE BITCH AND IT IS THE POOR MANS PS3. IF NINTENDO WII WAS A MAN IT WOULD HAVE A VERY SMALL PENIS AND STILL BE A VIRGIN YOU GUYS ARE SO JEALOUS THAT I HAD THE FIRST PS3 EVER AND I WILL DOMINATE ANYONE IN "RESISTANCE : FALL OF MAN"
    Reply
  • Wizzdo - Friday, January 14, 2011 - link

    Definitely a bigger head below than above! Reply
  • steveyoung123456789 - Friday, December 09, 2011 - link

    your a virgin pussy and if i ever find out where you live i will kick your ass!!!!!!!!!!!! Reply
  • steveyoung123456789 - Friday, December 09, 2011 - link

    Btw your a psycho for wanting to fuck a gaming cousel... smh.... queef!! Reply
  • SilverTrine - Friday, November 17, 2006 - link

    The GPU in the Ps3 is more than enough for what its intended for. Theres no magic in GPUs they're just specialized processors.

    In the Xbox360 the GPU carries more of the processing load. Remember the unified ram that the GPU uses in the Xbox360 is 700mhz fast.

    The GPU in the Ps3 also has 700mhz ram. However the Cell processor has access to XDR ram running at a whopping 3.2ghz! In the Ps3 system the Cell with the superfast XDR ram will do more of the grunt work and rely less on the GPU.

    Saying the GPU in the Xbox360 somehow gives the system is a mistake. What would you rather have doing processing work a GPU running relatively slow with 700mhz ram or a extremely fast Cell processor with 3.2ghz XDR ram?

    However utilizing this on the Ps3 will require more specialized programming, the Xbox360 because its fairly conventional will be able to tap more of its power sooner than the Ps3.
    Reply
  • theteamaqua - Tuesday, July 12, 2005 - link

    http://theconsolewars.blogspot.com/2005/05/xbox-36...
    i just wan people to know that how bias this site is, i mean this guy has no idea what he is talking about
    Reply
  • jwix - Wednesday, July 06, 2005 - link

    #77 I wouldn't say Anand's article was "full of shit." I would say it was a bit sensationlist, as stated in the Arstechnica article. What surprised me more than anything was that Anand would post such an article, then remove it so quickly. That's not his style.
    Bottom line though - these consoles will offer nothing new or innovative in the way of gameplay. I think I'll stick with my PC and Nintendo DS for now.
    Reply
  • steveyoung123456789 - Friday, December 09, 2011 - link

    get a life Reply
  • calimero - Wednesday, July 06, 2005 - link

    http://arstechnica.com/news.ars/post/20050629-5054...

    btw Anand article was "full of shit" (sorry but that is the right phrase) and it's not odd that Anand pull it. It's quite embarassing for Anand; someone already told: one thing is to write test of CPU speed and speed of graphics card in games... and another to analyse CPU architecture.
    Reply
  • jwix - Tuesday, July 05, 2005 - link

    Creathir - the article was reposted on other forums around the net. Here is the story in summary - Sony & Microsoft have both overhyped the processing power of their cpu's by using clever marketing speak. It turns out the processor designs are uneccessarily complicated, inefficient at crunching today's game code, and unlikely to be useful when game code finally becomes fully multi-threaded in the coming years. Why microsoft and sony didn't go with an Intel or AMD design, I don't know. The article speculates that both companies wanted IP rights to the cpu, maybe that's the reason.
    The GPU's on the other hand look plenty powerful. They should both be relatively equivalent in performance to the R520 and the current 7800 GTX.
    Bottom line - the new consoles will be quite powerful compared to the previous generation. However, PC's will still be more powerful, and wil remain the platform of choice for high end gaming. Something I was glad to read as I just built a new pc.

    Reply

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