Xbox Team on Backwards Compatibility Options

[kowrip]

This seems to be a good example of the general level of understanding of emulation. The 733 MHz Intel CISC processor in the xbox is very difficult to emulate using a 3200 MHz PPC RISC tri-core processor. MS is not using a just a single core for the emulation, they are using all 3 and it is barely enough power. Many instructions on the Intel CPU that take just a single clock require hundreds of clocks in overhead and execution on the RISC processor. This is because the RISC processor simply does not have the large set of instructions that the Intel CPU has.

HUNDREDS of clocks on the RISC ? What's an example of a CISC instruction that would take "hundreds" of clock ticks on a RISC processor ? I'd like to know. I'm aware of the different types of instruction sets, but I find it hard to believe that a single instruction would need hundreds of clock ticks to be executed on RISC.

[thax]

HUNDREDS of clocks on the RISC ? What's an example of a CISC instruction that would take "hundreds" of clock ticks on a RISC processor ? I'd like to know. I'm aware of the different types of instruction sets, but I find it hard to believe that a single instruction would need hundreds of clock ticks to be executed on RISC.

A matrix multiplication.

[thax]

1. We're not talking about an underground emulation group, who have to reverse engineer both consoles in order to work out how things are going to calculate - although MS don't own the intellectual rights to the Xbox, it's still their console as is the 360.

They still need to reverse engineer the games, which is the hard part of the equation. The hardware specifications give the team what the hardware should do, but sometimes there are undocumented instructions or behaviour that doesn't match specifications.

2. These guys are top-level programmers who should be able to do this stuff in their sleep. MS only hire the best for the job- they have the money to do this, remember?

There is only so good a human can get, the law of deminishing returns applies. MS does not genetically modify their employees to be super humans. Building an emulation engine of a complex platform is time consuming.

3. The programmers have had the Xbox 360 a LOT longer than a few months. I would imagine that it's been over a YEAR now since the first development kit has been available within MS itself.

The final kit has been around for only about 6 months now. Althought the emulation work probably started about a year ago, as MS decided to offer BC late in the game.

I'm 99% sure MS could write an emulator for the 360 and have it listed in the Dashboard for us to just insert an Xbox game and play it. There are too many commercial reasons why this wouldn't happen.

If MS could release a 100% perfect backward emulation engine they would as it would boost sales of the x360, which is the platform that MS wants to be successful. It makes sense because if the x360 acheives market dominance they will make more money then the small amount they would realise with the legacy xbox sales. In addition the venture in the console arena is a fight to control the living room for MS, when MS is not in the dominant market postion they do not hold back.

[kowrip]

A matrix multiplication.

A matrix multiplication is NOT a single instruction. What is the name of the instruction that does a matrix multiply ? I have the entire Intel Celeron instruction set reference right in front of me. The word matrix doesn't even appear in there. Regardless, even if there are some complicated instructions in CISC, the cost-per-instruction is much higher for CISC. So, if it takes a RISC processor 50 instructions to accomplish the same thing, it still wouldn't be 50 times as long because the cost-per-instruction is much less on RISC.

This post has been edited by kowrip: Apr 7 2006, 01:21 AM

[madmab]

Translation. We lied about Xbox backward compatibility just to fool you into justifying getting the 360 while selling off your Xbox to help pay for the high cost of it.

I saw this lame excuse coming over 6 months ago.

Waaa waaa waaa.

[Martinchris23]

They still need to reverse engineer the games, which is the hard part of the equation. The hardware specifications give the team what the hardware should do, but sometimes there are undocumented instructions or behaviour that doesn't match specifications.

The hardware is the lowest common denominator - all Xbox games are created to work with it. MS know the architecture since they wrote the XDK for developers. Surely with this amount of knowledge, writing a software emulator wouldn't be *that* hard?

The final kit has been around for only about 6 months now. Althought the emulation work probably started about a year ago, as MS decided to offer BC late in the game.

The RETAIL kit was released to the public around 6 months ago with Halo and Halo2 being BC out of the box. Why? Because Bungie knew Halo 3 was still a long way away. A lot of consecutive games have the same engine from year to year - take FIFA 2004. There really is no difference between this and FIFA 06 - you can tell because the same bugs are there year after year. As I said, Black has been out for no time at all and is already BC - doesn't this strike you as a little suspicious?

[arcice3]

its a shame no one could leak the emulator out like everthing else m$ makes gets leaked.. even after all these years there still isnt a decent emulator .. that i know of any ways

[KAGE360]

The hardware is the lowest common denominator - all Xbox games are created to work with it. MS know the architecture since they wrote the XDK for developers. Surely with this amount of knowledge, writing a software emulator wouldn't be *that* hard?

knowing the architecture is only part of the problem. making a specific architecture "act" like another architecture that is vastly different is not easy at all.

The RETAIL kit was released to the public around 6 months ago with Halo and Halo2 being BC out of the box. Why? Because Bungie knew Halo 3 was still a long way away. A lot of consecutive games have the same engine from year to year - take FIFA 2004. There really is no difference between this and FIFA 06 - you can tell because the same bugs are there year after year. As I said, Black has been out for no time at all and is already BC - doesn't this strike you as a little suspicious?

final dev kits were released the august before launch. bungie has nothing to do with BC beyond providing the source code to the BC team. yes halo 1 and halo 2 were BC out of the box but bungie/MS also admitted that the emulator wasnt finished. obviously they were going to spend the most time optimizing and perfecting the emu. code for halos, its their biggest franchise, but you can only do so much planning and coding until you get the final hardware. why is it a little suspicious that black got on the BC list so soon after its release? all this tells me is that all of the interviews and reports of the team tackling each game on a request bases is true. of course black would be added fast, it was in high demand, that is why a lot of people and reports were dissapointed about no BC on its release day. all this tells me is that MS is listening.

and about this whole BS theory of them holding off on some games and being able to emulate 100% if they wanted is rubbish. lets see, MS is in the business to make not spend money, so they are going to drag on the BC development just so they could pay a team of people hundreds of thousands of dollars to develop something they wont be making money off of? give me a break, if it was up to MS they would have 100% of the games BC and put the staff to better use developing features/tools/software that would actually make MS money. like it was stated before, MS does not hold back until they get what they want.

[Martinchris23]

I do see where you're coming from Kage360, but I don't think MS actually WANTED BC with the 360. It was only due to public outcry that they actually decided to spend some bucks and make it work.

Also, what's with this condition affecting a few games on the list?

"Currently the North American versions of these games are the only ones supported as backward compatible titles on Xbox 360"

Can there really be that much difference technically between PAL and NTSC versions?

I would LOVE to see how many people requested Black for the 360 - could there be as many as those who have been SCREAMING for FIFA 06? Any coincidence that there isn't a 360 release for Black?

[KAGE360]

I do see where you're coming from Kage360, but I don't think MS actually WANTED BC with the 360. It was only due to public outcry that they actually decided to spend some bucks and make it work.

Also, what's with this condition affecting a few games on the list?

"Currently the North American versions of these games are the only ones supported as backward compatible titles on Xbox 360"

Can there really be that much difference technically between PAL and NTSC versions?

I would LOVE to see how many people requested Black for the 360 - could there be as many as those who have been SCREAMING for FIFA 06? Any coincidence that there isn't a 360 release for Black?

of course MS didnt think of BC in the beginning, i think they made it clear from the start that they werent developing their next gen system with BC in mind and im happy they did it that way.

as for the region specific BC game list, i imagine it has to do with the programming required for games to work in the region. like the 360, its up to the developers if they wanted a xbox game to be region specific. between what is programmed in the game and the systems themselves there are plenty of reasons why there is different number of games on each region's BC list.

there obviously were enough people wanting black to be BC because like i said before, as the games launch game and went there were complaints and articles posted all over the net of how it was not BC. i hightly doubt that the demand for FIFA was really that high as many footbal/soccer fans consider it a sub-par game compared to winning eleven and also for the fact that FIFA was one of the next gen titles on EA's line up. and no there isnt any coincidence that their isnt a 360 release for black, regardless of the level of enhancements, it still takes a good amount of time to bring it near the level of what gamers expect on the 360.

[spinr34]

ok, there's a lot of stuff going on here and i agree with the people that agree with the devs emulation isn't easy and while the original xbox isn't a real monster of a machine, emulating all parts and different architectures isn't easy. anyways having said that, MS's main reason for emulating BC is because of the different architectures and their lack of IP over the parts in the original xbox. so that MIGHT mean you could see something like sony's approach on the next xbox by actually including the parts needed.

[thax]

A matrix multiplication is NOT a single instruction. What is the name of the instruction that does a matrix multiply ? I have the entire Intel Celeron instruction set reference right in front of me. The word matrix doesn't even appear in there. Regardless, even if there are some complicated instructions in CISC, the cost-per-instruction is much higher for CISC. So, if it takes a RISC processor 50 instructions to accomplish the same thing, it still wouldn't be 50 times as long because the cost-per-instruction is much less on RISC.

I agree with your explaination. My counter response was originally for someone who thinks that a PPC can execute every intruction that the celey does clock for clock on a single core.

The fact that the emulation developer stated that they need all 3 cores to do the emulation means that some instructions take much more work the emulate than a simple 1:1 instruction map.

When I used the reference of "require hundreds of clocks in overhead and execution" I meant that the code that the emulation engine must use to emulation the instruction may take hundreds of instructions. This isn't a strict 4 cycle celey vs. 26 cycle PPC comparison because we don't know how tight the code is in the emulation engine, thus I used the word "overhead".

[kowrip]

I agree with your explaination. My counter response was originally for someone who thinks that a PPC can execute every intruction that the celey does clock for clock on a single core.

The fact that the emulation developer stated that they need all 3 cores to do the emulation means that some instructions take much more work the emulate than a simple 1:1 instruction map.

When I used the reference of "require hundreds of clocks in overhead and execution" I meant that the code that the emulation engine must use to emulation the instruction may take hundreds of instructions. This isn't a strict 4 cycle celey vs. 26 cycle PPC comparison because we don't know how tight the code is in the emulation engine, thus I used the word "overhead".

Right, and I agree. There's certainly going to be overhead with emulating, especially when using drastically different architectures. However, 3 PPC cores at 3.2GHz is a HELL of a lot more power than the 733 Celeron has. They were making it seem like they were trying to emulate something that was only marginally weaker in performance, which is simply not true.

[DWells55]

Let's see here....

3.2GHz x 3 vs 733MHz.... yeah...
X1900XT based vs GeForce3 based.... yeah...
512MB GDDR3 vs 64MB RAM... yeah...

So why can't the 360 run Halo 2 right?

I know, systems need to be substantially more powerful to emnulate, but the Xbox was basically a PC, and 360 is substantially more powerful.

[EugeneEW3RD]

Well, even though the XBOX & XBOX 360 use PC hardware, we are dealing with game systems here. The games written for the XBOX are tied to the specs of the XBOX which is a 733 MHZ CPU, Nvidia GPU, 64 MB of ram, et al.

The XBOX 360 uses a 3.2 GHZ CPU running 3 cores, 512 MB of ram, ATI GPU, et al.

This is the main reason why it is harder to emulate the XBOX on the 360 because the specs are totally different. While the XBOX & 360 support DirectX, the DirectX on XBOX is tied to the specs of the XBOX.

This post has been edited by EugeneEW3RD: Apr 30 2006, 11:04 PM