Inside Microsoft's Xbox 360
by Anand Lal Shimpi, Kristopher Kubicki & Tuan Nguyen on November 16, 2005 5:09 AM EST- Posted in
- Systems
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.
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):
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:
We have previously discussed the Xbox 360's CPU in much greater detail, which you can read about here.
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Zebo - Friday, November 18, 2005 - link
I've made this correction before as well but Anand's not listening..that's alright he's the man.Googer - Wednesday, November 16, 2005 - link
I am getting a 404 error when I click on the photographs.Googer - Wednesday, November 16, 2005 - link
Thanks Anand, Kris, and Tuan for taking it apart so we can see what is inside of it. Awesome article, keep up the good work.MAME - Wednesday, November 16, 2005 - link
article is way f'ed up guysKilim - Thursday, November 17, 2005 - link
Don't worry, be happy, bucko. Sorry for being so damn right cheery right now, I had my therapist appointment last night, lol, and I feel good. hahaAnyway, I pre-ordered a 360 for my godson at the local Gamestop, well the one I work at, on June 18th, and he will now be waiting for the second shipment! We are only getting 26! Only 26 "good ones" and two "core" units. Anyone know what exact part of the building process is holding up construction of the 360's.
Is it the video card, cpu, what? Is it the HDD and that is why they created the core unit? Anyone know? Anand?
Imazalil - Thursday, November 17, 2005 - link
As far as I know, Microsoft is keeping the supply really limited to make sure that they have a 'sellout' launch. No real technical issues, just marketing.Shlong - Wednesday, November 16, 2005 - link
Wow that power supply is a beastpossnfiffer - Thursday, December 30, 2010 - link
Hey precioustone very general comment with a link i sense spam how bout a mod removes that one. anywayz nice pix got mine opensteveyoung123456789 - Friday, December 9, 2011 - link
wow guys im learning so much and this is so fin thanks alot!! :).... jk your all fags go diedarckhart - Sunday, April 7, 2013 - link
Update: Just in case anyone else browses here to use as a guide.I cracked open a Zephyr model yesterday using brand new torx key sets. The only required ones are T8 and T10. I posted a photo guide here: http://i.imgur.com/IQzr0k8.jpg