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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  • yacoub - Thursday, November 17, 2005 - link

    Considering they were corrected by someone else in a previous article about "dies/dice" and are still making the same mistake, it's important to make sure they fix it this time before it becomes a permanent fixture of this site.

    And yes, that's really all I thought was worthy of mentioning. The review is pretty cool.
    Reply
  • Anand Lal Shimpi - Thursday, November 17, 2005 - link

    According to Microsoft and Intel, the plural of 'die' when referring to a CPU die, is 'dice'.

    Microsoft's internal documentation talking about the Xbox 360 also refers to the ATI Xenos GPU as having two dice.

    I am waiting for responses on other chip makers to make sure that the correct form of the word is dice.

    Take care,
    Anand
    Reply
  • gamigin - Thursday, November 17, 2005 - link

    Anand,

    Do you have any evidence to back up the following quote in spite of game developers claiming otherwise?

    "game developers shouldn't run into capacity limitations on Xbox 360 discs anytime soon"



    BTW, the plural of a manufacturing die is dies. If Microsoft or Intel said dice, then they are just wrong.
    Reply
  • Phantronius - Thursday, November 17, 2005 - link

    Who are you, my fucking English teacher? Reply
  • yacoub - Thursday, November 17, 2005 - link

    Very interesting! Thanks for taking the time to respond, Anand.

    I wouldn't be surprised if it simply slipped through marketing department editing, considering dictionary.com is saying it should be "dies". "Dice" is normally only ever for the six-sided tools of chance/gambling.

    If they're creating a new use for the term, that in itself would be pretty noteworthy as well.
    Reply
  • Anand Lal Shimpi - Thursday, November 17, 2005 - link

    Well the term dice is what the CPU architects use, so I don't think it's a marketing/PR mishap.

    Take care,
    Anand
    Reply
  • gamigin - Thursday, November 17, 2005 - link

    Most CPU architects certainly do not use the term "dice" as the plural to a manufacturing die.

    It's probably the same Microsoft guys who standardized the non-word "canonicalize"
    Reply
  • Kilim - Thursday, November 17, 2005 - link

    Ah dude, are you saying that "normal" dice are only for six sided dice? Ohhhh, someone is trying to get the D&D guys to start flaming him, lol. =p. Reply
  • linuxOwnzIfUrLeet - Thursday, November 17, 2005 - link

    I lost the link to the mod chip can someone post?
    Reply
  • LoneWolf15 - Thursday, November 17, 2005 - link

    1) If I buy the cheaper XBox360, how easy is it to add my own notebook hard disk later if I want it? Would have been very useful to know, and wasn't made clear.
    2) Media playback compatibility info --I'm sure the unit can play DVD's, and probably MP3's, but can it play DivX content? Xvid? MPEG-4 or HD WMV? These would be good things to know. A video game console has moderate usefulness to me; a video game console with broad media playback capabilities far more so.

    Finally, a comment to Microsoft: If the Xbox360 had Media Center compatibility (read: PVR), I'd have bought it in a heartbeat without having to think about it. It would be the perfect home theater convergence device. It's really too bad this wasn't an option.
    Reply

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