The Xbox 360 CPU

The original Xbox used a hybrid mobile Pentium III/Celeron processor, but for the 360 Microsoft went to IBM and got the rights to a PowerPC core.  The move to the PowerPC instruction set meant that there would be no direct binary compatibility with older Xbox titles, but the sacrifice was obviously deemed necessary by Microsoft. 

The CPU itself features three of these PowerPC cores and is currently manufactured on a 90nm process, however Microsoft will most likely be transitioning to 65nm as soon as possible in order to reduce the die size and thus manufacturing costs.  Remember that a die shrink from 90nm down to 65nm will cut the size of the CPU in half, and should be possible for Microsoft sometime before the end of next year. 


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All three cores are identical and feature a 2-issue pipeline and can only execute instructions in-order; we've already discussed the reasoning behind this decision here.  The impact of the in-order execution cores is generally a negative one on current game code, but by going with a much simpler core Microsoft was able to stick three of them on a die with hopes of making up for lost performance by enabling some pretty serious multithreading. 

Not only does the Xbox 360's CPU feature 3 cores, but each core is capable of executing two threads at the same time, making the CPU capable of simultaneously executing 6 threads.  Unfortunately, most titles appear to be only using one or two threads for the majority of their game code, with the remaining threads being used for things like audio encoding/decoding, real-time decompression of game data off of the DVD-ROM and video decoding. 

Microsoft has their own license to use and manufacture the CPU used in the Xbox 360, and thus we see their logo on the chip itself.  Microsoft cools the 3-core CPU using a fairly beefy heatsink outfitted with heatpipes (pictured below): 


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Airflow is supplied by the two rear fans in the Xbox 360; the air is channeled over the GPU and CPU heatsinks using a duct. The larger heatsink on the right is atop the CPU, the smaller heatsink is for the GPU:


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We have previously discussed the Xbox 360's CPU in much greater detail, which you can read about here.

Removing the Heatsinks from the Motherboard The Xbox 360 GPU
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  • fuzzynavel - Wednesday, November 16, 2005 - link

    Thanks for the article....shame slash-dot has killed your bandwidth!!

    Seems like a good point about overheating...maybe worth waiting till 65nm chips start showing up...won't get one in the UK till way after christmas anyway!!(haven't pre-ordered)
    Reply
  • Face27 - Wednesday, November 16, 2005 - link

    Is it my connection or is anandtech being really slow, its not loading any of the pictures which is what I wanna look at. I'm guessing this is quite a popular article. Reply
  • zech - Wednesday, November 16, 2005 - link

    The article was slashdotted:
    http://games.slashdot.org/games/05/11/16/1432205.s...">http://games.slashdot.org/games/05/11/1...5.shtml?...

    Anandtech's servers aren't handling this /. very well. But this is one of the first Xbox360 interal reviews (in a PC-hardware sort of fashion), so I'm sure every Xbox360 forum out there is posting links to it.
    Reply
  • ItsOnlyMonday - Wednesday, November 16, 2005 - link

    Yes, these pictures are on multiple forums, somee even lack proper credits.. :-\ Reply
  • gamigin - Wednesday, November 16, 2005 - link

    [quote]
    game developers shouldn't run into capacity limitations on Xbox 360 discs anytime soon
    [/quote]

    Prominent game developers disagree

    From "http://www.eurogamer.net/article.php?article_id=56...">http://www.eurogamer.net/article.php?article_id=56.... Note that this interview was before the next gen console debate in 2004.
    [quote]
    The danger is currently the storage medium (DVD), and one we thing we’re all praying for in the next round of hardware is that they don’t just go, ‘It’s DVD again’. We’ve done some clever stuff with compressing it, but we were virtually full on the disc with Vice City – this time we’re overfilling the disc to the max.”
    [/quote]
    Reply
  • quanta - Wednesday, November 16, 2005 - link

    If the developers worry about that much on not enough space to store sound samples, they should have invested on text to speech technology a long time ago, instead of relying on prerecorded sample. Unlike the cheesy Macintalk TTS in the 1980s, modern TTS can accurately simulate human speeches, even the emotional tones. Hey, Ananova uses it, does it not? That way the developers don't even have to worry about rehiring dead/retired/on-strike workers doing voices for games based on century-old movies! Reply
  • gamigin - Wednesday, November 16, 2005 - link

    Voice synthesis is great but it's really not at the point of replacing voice actors for dramatic games. Can you imagine watching a movie with the voices of your favorite actor dubbed in by a computer? Not quite the same.

    Also, it's more than just voice overs; a lot of space is used for graphics, models, textures, landscapes, animation data, sound effects, and music.

    Most current games don't need more capacity than standard DVD at the moment but some definitely do and others could at least take advantage of it.
    Reply
  • quanta - Wednesday, November 16, 2005 - link

    Actually, the emotionalal aspect of TTS is already been done by http://www.computing.dundee.ac.uk/staff/irmurray/s...">various people. In fact, many commercial grade TTS software that supports http://www.w3.org/TR/speech-synthesis/">SSML already able generate emotionally sounding voices. It's not Microsoft's fault that game developers don't try to use/refine the existing TTS engines to make them usable for voice acting applications. Reply
  • Xenoterranos - Thursday, November 17, 2005 - link

    Ywah, sure, but can you get a computer to do a dead-on Ray Liotta? I think not my friends, I think not! Reply
  • quanta - Tuesday, December 06, 2005 - link

    Why don't you try it first before commenting? You can find some demos on http://www.nuance.com/realspeak/rvoice/english.asp">Nuance rVoice's site. Depending on the title, the TTS voices sound better than the real live voices in some games. Reply

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