Why is x86 being dropped by Microsoft for new Xbox?

[duncan36]

I realize that x86 is some 20+ years old now, and its remarkable how addons to this system have made it perform quite well in things like 3d graphics and sound. However am I right in assuming that inefficincies in x86 make it less attractive for a new gaming console?

Basically I am interested in knowing the ins and outs of this decision and why x86 is not as good for a gaming console as a custom system. Thanks all for their input.

 

[mesyn191]

I don't think it has anything to do with "x86 not being good as Cell/Xenon", Xbox showed quite clearly that it was possible to have a good console with a mediocre CPU if other parts could make up for it (ie. they could've put a PPU in X360 if they really wanted, or had Intel or AMD put in some sort of crazy SIMD unit, not unlike what Xenon does for each of its CPU's).

I think its all cost (MS wasn't able to get Intel to lower the cost on the CPU and while fairly cheap in beginning its now taking a big chunk of the Xbox's cost, MS can have Xenon shrunk however they like and scale costs down over the X360's lifetime), liscensing (no way Intel or AMD would've allowed MS to own the licensce on thier IP), and heat issues.

 

[Entropy]

While x86 is an architecture originally intended to shuffle clerical data (bytes) cheaply, it certainly has evolved a bit from that into a more general purpose architecture most notably with the addition of x87 stack based FP and subsequently simple vector functionality.
But it still targets the personal office computer. That is where the volume and long term viability of the platform resides.

Not targeting office application, the console CPUs take a somewhat different approach.
+ They are multi core designs
+ The cores provide higher floating point performance in a more flexible environment
+ They provide higher memory bandwidth to the cores
+ They provide much better coprocessor (GPU) communication
- They sacrifice single thread integer performance for badly scheduled code

The above is common to both the XBox2 and the PS3 CPUs.
The only thing which is easily adressed by existing x86 is going to dual core, although the dual core designs coming out of Intel and AMD are not as tightly integrated as either of the console designs, but more resemble two separate CPUs crammed onto the same die. Going beyond two x86 cores would hardly be an option given console launch time frames.

 

[Magnum PI]

Xbox showed quite clearly that it was possible to have a good console with a mediocre CPU.

microsoft showed quite clearly it was possible to have a good console with a mediocre CPU, if you are ready to lose billions of dollars.

 

[Lacero]

microsoft showed quite clearly it was possible to have a good console with a mediocre CPU, if you are ready to lose billions of dollars.

How are loosing billions connected to having a "good console with a mediocre CPU"?

 

[Magnum PI]

The only thing which is easily adressed by existing x86 is going to dual core, although the dual core designs coming out of Intel and AMD are not as tightly integrated as either of the console designs, but more resemble two separate CPUs crammed onto the same die.

it is true for intel dual core, not for AMD which are better integrated than intel:
http://www.behardware.com/articles/571-1/dual-core-athlon-64-x2-4800-and-4400.html

i fail to see how a dual-core powerpc like the 970MP is more integrated than a dual-core AMD.

 

[Magnum PI]

How are loosing billions connected to having a "good console with a mediocre CPU"?

the original question of the thread is "Why is x86 being dropped by Microsoft for new Xbox?"

the fact that xbox used a x86 cpu does not show x86 is a viable choice for a console, despite the quality of the xbox as a console, because microsoft loose billions with the xbox, and the choice of a x86 cpu may have something to do with that.

because of its total lack of rentability you can't really say that any of the choices microsoft made for the xbox was a good one.

 

[croc hunter2]

maybe, just maybe, MS did some research and came to the same conclusion as the people at Sony. Parallel FP performance was far more important on a machine whose major job is to deal with multimedia applications than the OOE on the general purpose x86 line.

2 competing teams come to the same conclusion. They must reckon there is something in that.

 

[deathstar121]

While x86 is an architecture originally intended to shuffle clerical data (bytes) cheaply, it certainly has evolved a bit from that into a more general purpose architecture most notably with the addition of x87 stack based FP and subsequently simple vector functionality.
But it still targets the personal office computer. That is where the volume and long term viability of the platform resides.

Not targeting office application, the console CPUs take a somewhat different approach.
+ They are multi core designs
+ The cores provide higher floating point performance in a more flexible environment
+ They provide higher memory bandwidth to the cores
+ They provide much better coprocessor (GPU) communication
- They sacrifice single thread integer performance for badly scheduled code

The above is common to both the XBox2 and the PS3 CPUs.
The only thing which is easily adressed by existing x86 is going to dual core, although the dual core designs coming out of Intel and AMD are not as tightly integrated as either of the console designs, but more resemble two separate CPUs crammed onto the same die. Going beyond two x86 cores would hardly be an option given console launch time frames.

Here's another + it makes for easy ports between PS3 and 360.

 

[Gollum]

Architectural differences aside, owning the IP to the CPU is certainly a primary motivation - something that'd be impossible with both x86 architectures from AMD and Intel. We have discussedd the resons for owning the IP before, main benefit is of course costs (not dependant on somebody else dictating the price).

Also, Sony has been quite outspoken about Cell's novel, FP heavy design and MS is not stpuid. A x86 CPU will not compare favourably with Cell in charts, its not exactly a poster-boy for good a good balance of theoretical throughput per transitor. Xenon is IMO sort of an attempt to not completely abandon classical CPU architecture, yet offering significantly improvements in theoretical performance, both at reduced costs. We'll see how it fares in practice...

 

[mesyn191]

microsoft showed quite clearly it was possible to have a good console with a mediocre CPU, if you are ready to lose billions of dollars.

I don't agree with this, just cuz a console's CPU is x86 doesn't garuntee that you'll loose billions of dollars. Given enough time/money I think either Intel, AMD, Cyrix/VIA (don't laugh, current Cyrix CPUs are very similar to one of the CPU's in Xenon (ie. very high clock speed, small die size, low heat, in order processing (or is it very minimal OoOE?...I know the early versions were in order only), and a fairly powerful SSE2 FPU (not as good as VX or whatever it is the FP unit in Xenon is called but then SIMD units scale very well by just slapping more of em' on die or by making them wider...)) or even IBM (they do have rights to produce a x86 CPU IIRC, I know they fabbed the Cyrix 6x86's and MII's) could've designed a x86 CPU that would've been competitive performance and cost wise (as far as the die size is concerned anyways, I wouldn't speculate much as far as IP ownership goes...).

 

[duncan36]

Ok with cell you can easily do physics calculations. However there are physics boards being produced for x86 systems. Given that the pure processing power of x86 cpus is high. What is keeping these chips from being able to do physics that newer games will want?
Is it the fact that in our PCs so many CPU cycles are used up just running the system.

Whats up here?

 

[Carl B]

Ok with cell you can easily do physics calculations. However there are physics boards being produced for x86 systems. Given that the pure processing power of x86 cpus is high. What is keeping these chips from being able to do physics that newer games will want?
Is it the fact that in our PCs so many CPU cycles are used up just running the system.

Whats up here?

If you want to apply that architectural model to the XBox though, that's still another chip required for the system - and chips add cost. I think the Cell will be 'the' physics chip, but that doesn't even mean that devs will utilize is to it's fullest extent. And in that sense I think the 360 will be good with assigning one of it's cores to the task. That's honestly the way it'll play out most frequently on the desktop space as well as dual-cores become more and more common, and games begin to incorporate that.

I mean, I don't know about you, but I'm not going to be buying a seperate physics card...

 

[duncan36]

So I think this leads into another question why not use a dual-core chip for the Xbox 2 and an Xbox style PC based architecture?
Is it really that much cheaper to design a completely new architecture, build plants to build it rather than get off the shelf PC parts?

Or is there some great gain in efficency?

 

[darkblu]

it's not cheaper to design it, it's cheaper to produce it over the projected lifespan, plus you get a better price/performance ratio over the same period.

 

[duncan36]

And thats because x86 is inefficent to some degree? If thats the case can anyone answer what exactly causes x86 to be more inefficent and therefore costly.

 

[Carl B]

And thats because x86 is inefficent to some degree? If thats the case can anyone answer what exactly causes x86 to be more inefficent and therefore costly.

It's not costly because it's inefficient, it's costly because if you want it, you need to purchase from Intel, AMD, VIA, or Transmeta. Now - maybe a custom chip from one of the later two would have been an interesting thing indeed, but the core of the argument is that owning the IP and being able to call the shots on fabbing, Microsoft is able to have greater control over one of their primary costs, whereas in the Xbox gen they were more or less taken for a ride by Intel and NVidia.

 

[duncan36]

Well Nintendo used an IBM cpu. It was a slower model suggesting that since they used a custom architecture they were able to squeeze more power out of their system even with a slower processor.

The contract Microsoft negotiated with Nvidia was costly I agree. If they'd have designed most of the system inhouse rather than paying Nvidia to do so I dont see why they couldnt have designed the Xbox relatively cost effectively.

 

[PG2G]

I think its just a matter of choosing the best tool for the specific application domain. The software run on a desktop computer doesn't necessarily have the same bottlenecks and hardware requirements as the software that is run on a game console.

 

[Magnum PI]

I don't agree with this, just cuz a console's CPU is x86 doesn't garuntee that you'll loose billions of dollars..

i don't say that, i say that the fact x86 was used in the xbox does not prove x86 is a good choice for a console. i neither proves that using x86 guarantees that you'll loose lots of money.

it proves nothing.

it would have proven something it if the xbox had been a financial success.