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.
Facebook
Twitter
RSS
93 Comments
View All Comments
jotch - Friday, June 24, 2005 - link
#20 well that can't be right for the whole consumer base, as I'm 24 and only know other adults that have consoles and alot of them have flashy tv's for them as well, I do. I think if you look at the market for consoles it is mainly teens and adults that have consoles - not kids. Alot of people I know started with a NES or an Atari 2500, etc and have continued to like games as they have grown up. Why is it that the best selling game has an 18 rating?? (GTA: San Andreas)The burning of the screen would be minimal unless you have a game paused for hours and the tv left on - TV technology is moving on and they often turn themselves off if a static image is displayed for an amount of time. So burning shouldn't occur.
nserra - Friday, June 24, 2005 - link
All the people that i know having consoles is kids (80%), and their parents have bought an TV just for the console, an 70€ TV.....Who is the parent that will let kids on an LCD or PLASMA (3000€) to play games (burn them).
Or there will be good 480i "compatibility" in games, or forget it....
#17 I agree.
fitten - Friday, June 24, 2005 - link
#14 There are a number of issues being discussed.For example, given the nature of current AI code, making that code parallel (as in more than one thread executing AI code working together) seems non-trivial. Data dependencies and the very branch heavy code making data dependencies less predictable probably cause headaches here. Sure, one could probably take the simple approach and say one thread for AI, one for physics, one for blah but that has already been discussed by numerous people as a possibility.
Parallel code comes in many flavors. The parallelism in the graphics card, for instance, is sometimes classified as "embarassingly parallel" which means it's trivial to do. Then there are pipelines (dataflow) which CPUs and GPUs also use. These are usually fairly easy too because the data partitioning is pretty easy. You break out a thread for each overall task that you want to do. You want to do OpA on the data, then OpB, then OpC. All OpB depends on is the output data of OpA and OpC just depends on OpB's final product. Three threads, each one doing an Op on the output of the previous.
Then there are codes that are quite a bit more complex where, for example, there are numerous threads that all execute on parts of the whole data instead of all of it at once but the solution they are solving for requires many iterations on the data and at the end of each iteration, all the threads exchange data with each other (or just their 'neighbors') so that the next iteration can be performed. These are a bit more work to develop.
Anyway, I got long-winded anyway. Basically... there are *many* kinds of parallelism and many kinds of algorithms and implementations of parallelism. Some are low hanging fruit and some are non-trivial. Since I've already read that numerous developers for each platform already see low hanging fruit (run one thread for AI, another for physics, etc.) I can only believe they are talking about things that are non-trivial, such as a multithreaded AI engine, for example (again, as opposed to just breaking out the AI engine into one thread seperate from the rest of game play).
probedb - Friday, June 24, 2005 - link
Nice article! I'll wait till they're both out and have a play before I buy either. Last console I bought was an original PlayStation :) But gotta love that hi-def loveliness at last!#3 yeah 1080i is interlaced and at such a high res and low refresh the text is really difficult to read, it'd be far better at 1080p I think since that would effectively be the same as 1920x1080 on a normal monitor. 1080i is flickery as hell for me for desktop use but fine for any video and media centre type interfaces on the PC.
A5 - Friday, June 24, 2005 - link
You know, the vast majority of the TVs these systems will be hooked up to will only do 480i (standard TV)...jotch - Friday, June 24, 2005 - link
#14 - here here!jotch - Friday, June 24, 2005 - link
#10 - sounds to me like they're way ahead of they're time, future-proofing is good as they'll need another 6 years to develop the PS4 - but the Cell and Xenon will force developers to change their ways and will prepare them for the future of developing on PC's that eventually have this kind of CPU chip design (ref intel's chip design future pic on the first page of the article), like the article says the initial round of games will be single threaded etc etc...You might get alot of mediocre games but then you should get ones that really shine bright on the PS3, noticeably Unreal 3 and I bet the Gran Turismo (polyphony) guys will put in the effort.
Pannenkoek - Friday, June 24, 2005 - link
I'm quite tired of hearing how difficult it is to develop a multithreaded game. Only pathetic programmers can not grasp the concept of parallel code execution, it's not as if the current CPU/GPU duality does not qualify as one.knitecrow - Friday, June 24, 2005 - link
you'll need HDD for online service and MMOPhow many people are going to buy a $100 HDD if they don't have to?
LanceVance - Friday, June 24, 2005 - link
"the PS3 won’t ship with a hard drive"If that's true, then will it be like:
- PS2 Memory Card; non-included but standard equipment required by all games.
- PS2 Hard Drive; non-included and considered exotic unusual equipment and used by very few games.