Microsoft's Xbox 360, Sony's PS3 - A Hardware Discussion
by Anand Lal Shimpi & Derek Wilson on June 24, 2005 4:05 AM EST- Posted in
- GPUs
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.
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LanceVance - Friday, June 24, 2005 - link
Excellent article. Definitely the most thorough, informative, well researched article on the PS3/Xbox360.And most importantly, unlike every other article on the subject, it's not strongly biased toward one camp while making comments of substance.
yacoub - Friday, June 24, 2005 - link
I bet the PS3 debuts at a higher price.Also regarding statements made on the Conclusionary page:
--"That being said, it won’t be impossible to get the same level of performance out of the PS3, it will just take more work. In fact, specialized hardware can be significantly faster than general purpose hardware at certain tasks, giving the PS3 the potential to outperform the Xbox 360 in CPU tasks. It has yet to be seen how much work is required to truly exploit that potential however, and it will definitely be a while before we can truly answer that question."--
I find it funny that once again the PlayStation will be the harder system to code games for that take full advantage of its abilities. If trends mimic the past (as they often do) this will lead to a large amount of mediocre games by companies too small to afford the dev time necessary to take real advantage of the PS3's advantages or on deadlines too tight to spend the time doing more.
Furen - Friday, June 24, 2005 - link
It does sound pretty low but (I'm guessing) it's more than enough, I dont think they would have separated the dies unless it didnt lead to a big performance penalty. also, I'm guessing that the 256MB/sec bandwidth between the eDRAM and its processing hardware is 256GB/sec? Microsoft was using that number to inflate their "system bandwidth" total.Woodchuck2000 - Friday, June 24, 2005 - link
And for that matter, 32Mb/s inter-die communications in the Xenos GPU seems low to me:p
Good article though guys!
Furen - Friday, June 24, 2005 - link
Is there any word on the media center extender capabilities on the xbox 360? I think Microsoft mentioned something about that but I'm not sure if that was oficial or not. Just hope they allow us to plug in some video capture device and use it as a dvr eventually.As much as I like sony's playstation, I find it quite boring on the technical side. It seems like they're just throwing everything they can into it but nothing is really that exciting, or useful. Come on, dual-HDMI. I dont see myself having two HDTVs in such close proximity to each other. Gigabit router? Seems like they're desperate to use the extra cpu muscle. I wonder how heavy ethernet traffic will affect cpu usage.
Woodchuck2000 - Friday, June 24, 2005 - link
Surely porting between multi-core PC software and Xenon should be fairly trivial, not fairly Non-trivial as stated in the article...?jotch - Friday, June 24, 2005 - link
I stands for interlaced whilst the P stands for progressive scan. Check out the difference at http://en.wikipedia.org/wiki/720por
http://en.wikipedia.org/wiki/1080i
This should resolve this issue.
AnnihilatorX - Friday, June 24, 2005 - link
1080i = 720p doesn't it? 1080p is the one Xbox 360 doesn't support.These "i"s and "p"s are confusing me
sprockkets - Friday, June 24, 2005 - link
How is 1080i on your tv's? On my 1 year old Mitsubishi native 1080i tv using dvi from the computer at 1080i is basically useless since the text is too small and the image looks like the refresh rate is below 60hz, whereas HDTV broadcasts look fine. Using the other mode of 720x480 looked great.Will HD output from a console be any better than a video card in a computer? Is it just my tv?
Cmon, did you really think nVidia would release something far more advanced for a console than for a video card, or perhaps, more specifically, having it way outperform 6800 ultras in sli?
If you need around a 400w power supply for even non sli setup, what kind of heat and power will these new consoles need anyhow???
Of course I am more interested in how the PS3 will work with Linux more than games hahahahaha, since Sony officially mentioned it.
emmap - Sunday, December 4, 2005 - link
And that's this article, Sony and M$ have missed:it's not the number of megapixels, shader pipelines, CPU / GPU bandwidth, multithreaded or single threaded code which do a great game. It's imagination put in the game, gameplay, artistic art quality, human feeling we get looking at the characters, fun and so on. It's not only mathematics and physics: we don't love a game because it has X millions polygons or run at Y fps, no it's totally different. Just see all the mame fans out there, you'll see that they don't care about the obsolete hardware the game they are playing on, they care about the most important thing about game: ENTERTAINMENT!