Backwards compatibility on Xbox 360

[pipo]

New post on the Xbox Team blog: http://blogs.msdn.com/xboxteam/articles/On_Backwards_Compatibility.aspx

I'm certain that many of you have been waiting for us to say something about how backwards compatibility works on Xbox 360. It is a very complex topic, to say the least. Thanks to XboxFan, a member of the backwards compatibility development team here for providing a lot of these details.

So for example, during BC development we sometimes had problems with system link games. Once it was caused by the emulator missing a cryptographic key. Another time, it was caused by a very small precision error in floating point. Yet another time, it was caused by a subtle bug in the CPU emulator that caused it to take the wrong branch in the game’s internal state machine and ultimately (millions of instructions later) disconnect.

When debugging, the correctness of each individual part is what matters. However, it’s not the raw performance of each individual part that matters, but the performance of the system as a whole. Individual code routines might have excellent performance on their own, but when used together one part can interfere with another in many ways (including cache effects, CPU pipeline effects, lock contention, etc.). There are so many variables and so many different things that can be measured, and the act of measuring performance affects the performance of what you’re measuring.

Comes very close to rocket science IMHO...

 

[Legend]

I am wondering why MS is putting itself in all thes mess that is b/c with Box. they should have either put bc in mind from the beginning and designed X2 with that, or left it all together. is it really worth all the mess and confusion and media reports to support 20 or something games?

PS3 has bc not only for PS2, but even PSOne (an overkill if you asked me) and Rev looks to have no problems being bc with Cube (and some earlier games).

it feels like this was a last minute or aftert thought from MS...

 

[pipo]

It's to do with IP.

From the same link:

One way to do this is embed the parts of an original Xbox into an Xbox 360. This was the path Sony chose to use in PlayStation 2's compatibility. However, Microsoft doesn't own the intellectual property in Xbox: it's owned by various other companies including Intel. Microsoft wouldn't have the freedom to take the parts needed for compatibility, shrink them down, and put them inside Xbox 360.

Which is really old 'news' by the way.

 

[Bohdy]

Secondly, it’s not usually the performance of the emulator itself that matters, but rather the overall performance as perceived by the emulated Xbox game. Most of our work isn’t to improve the performance of the code we wrote, but rather to improve the performance of the emulated games.

I found this part really interesting. Does it mean that they are actually optimizing the original game code to use the virtual system more efficiently? I'm also disappointed that there was no mention of static recompilation, as I had surmised they would be using to get such performance, but maybe it is just one hell of an optimized dynarec.

 

[booomups]

they really could have saved themself the trouble with bc.

the only advantage would be if even NEW xbox1 games would run on the xbox360, so that a new xbox1 game would have a bigger userbase.

 

[Alpha_Spartan]

I am wondering why MS is putting itself in all thes mess that is b/c with Box. they should have either put bc in mind from the beginning and designed X2 with that, or left it all together. is it really worth all the mess and confusion and media reports to support 20 or something games?

PS3 has bc not only for PS2, but even PSOne (an overkill if you asked me) and Rev looks to have no problems being bc with Cube (and some earlier games).

it feels like this was a last minute or aftert thought from MS...

B/C is a mess on consoles and Sony set a precedent that will bite them, MS and Nintendo in the ass in the future. MS shouldn't have gone with b/c to begin with because of the inherent problems with it.

Due to the raw deal that Nvidia gave them and probably some issues with Intel, an "Xbox-on-a-chip" type implementation wasn't possible. Now, because somehow someone within MS convinced the higher-ups that b/c was a good idea, Microsoft has backed itself into a corner where they have to write emulators for individual games, which is a pain in the ass. Some type of Xbox virtual machine would have been better, but the software overhead would be rediculous (try running a 16-bit emulator like NTVDM.exe on an NT machine and then look at the CPU utilization to see what I mean). Soon Microsoft will have to abandon this waste of time and I would encourage them to do it sooner than later. B/c is a gimmick, always has been and always will be.

The need for b/c actually stifles a console. The main reason that Sony could include b/c in the PS2 is because they just used the PSX CPU/GPU as the I/O controller in the PS2. B/C came virtually for free. Something tells me that it won't be so cut and dry with the PS3. In the end Sony would have been better off by ditching b/c. Nintendo is getting it for free since the Revolution is nothing but an extension of GCN hardware. But then again, it's nothing to write home about.

I can't wait to see what sacrifices (if any) Sony made to include b/c in the PS3. IMHO, a console manufacturer has to make too many other sacrifices for backwards compatibility to cause another one. For example, if the RSX has to have trannies stripped so that Sony could put some type of hardware PS2 support in it, then I will be a bit miffed and you should be too. What if the RSX clockspeed has to be dropped because all the procs in the system exceeded Sony's thermal threshholds? What if the extra hardware raises production costs and thus retail costs go up? I'd rather have the PS3 performance that Sony promised last E3 for $400 than a b/c PS3 that is only equal or less powerful graphically than the Xbox 360 (and costs $100 more).

I would rather hear an announcement that PS3 won't be b/c than to hear that the PS3 specs have been downgraded. Additionally, I would have liked to seen beefier Revolution than one that could play the three GCN games I own. B/C just doesn't make any fucking sense to me when it comes to consoles. Sony set a bad precedent IMHO.

 

[Titanio]

B/C is a mess on consoles

It's a mess on (a) console, but usually it works fine, and is welcome.

I can't wait to see what sacrifices (if any) Sony made to include b/c in the PS3.

Cost, probably. Kutaragi has mooted that it is expensive for them to do BC "because of the hardware", but they want to do it right from the start.

Plus there is some potential benefit to the bottom lines of companies implementing BC, with the opportunity for re-selling older games on the new systems over the net.

 

[London Geezer]

I can't wait to see what sacrifices (if any) Sony made to include b/c in the PS3. IMHO, a console manufacturer has to make too many other sacrifices for backwards compatibility to cause another one. For example, if the RSX has to have trannies stripped so that Sony could put some type of hardware PS2 support in it, then I will be a bit miffed and you should be too. What if the RSX clockspeed has to be dropped because all the procs in the system exceeded Sony's thermal threshholds? What if the extra hardware raises production costs and thus retail costs go up? I'd rather have the PS3 performance that Sony promised last E3 for $400 than a b/c PS3 that is only equal or less powerful graphically than the Xbox 360 (and costs $100 more).

Why on earth should that happen? Thinking that Sony would trade off performance on PS3 games just to accommodate PS1/2 compatibility is pushing it a little bit. Sony can very well accommodate what is needed without taking things off the PS3 hardware, as has been speculated here.
If PS3 will only be equal or even less powerful than X360, it certainly won't be because of BC. And if for some strange reason it is, then Sony will need to be spanked hard.

I would rather hear an announcement that PS3 won't be b/c than to hear that the PS3 specs have been downgraded. Additionally, I would have liked to seen beefier Revolution than one that could play the three GCN games I own. B/C just doesn't make any fucking sense to me when it comes to consoles. Sony set a bad precedent IMHO.

Well that's just your opinion. I can't wait to play my PS2 games like SOTC and some others at 720p with AA - if Sony keep their promises of course...
Some PS2 games looked very good, the only thing keeping them from looking fantastic was the awful IQ at times. Fix that and i'll be happy to play them again for a bit until big PS3 games come out. And i'm sure millions of people think the same.

 

[Mmmkay]

Because you don't see the worth doesn't make its purpose redundant. According to NPD's purchase intent survey of 15,000 people, backwards compatibility was a highly sought after feature.

Besides brand loyalty, "Other factors mentioned were graphics capability, backwards compatibility, and the quality of the available content," said Frazier

The study also finds that the majority of current generation system owners who are very or somewhat likely to buy a new system plan on continuing to play with the system they currently own and more than half (58%) will continue purchasing games for the system they currently own.

Source

I do have to question your motives with that post though. It seems you're eager for the PS3 to be 'downgraded' in any possible way, but that not all downgrades are equal. Having your cake and eating it? To not deliver on B/C (TRC withstanding) is a serious downgrade in many people's eyes.

 

[Titanio]

Well that's just your opinion. I can't wait to play my PS2 games like SOTC and some others at 720p with AA - if Sony keep their promises of course...

One of the things about "Sony promises" is that half the time, Sony never made them Sony has said absolutely nothing about AA in PS2/PSone games. All they've said is that you'll be able to play them in HD, which probably means upscaling.

 

[London Geezer]

One of the things about "Sony promises" is that half the time, Sony never made them Sony has said absolutely nothing about AA in PS2/PSone games. All they've said is that you'll be able to play them in HD, which probably means upscaling.

I should have written "possibly with AA"... But for me, SOTC in 720p will be very nice indeed!!

 

[Shifty Geezer]

I can't wait to see what sacrifices (if any) Sony made to include b/c in the PS3. IMHO, a console manufacturer has to make too many other sacrifices for backwards compatibility to cause another one. For example, if the RSX has to have trannies stripped so that Sony could put some type of hardware PS2 support in it, then I will be a bit miffed and you should be too. What if the RSX clockspeed has to be dropped because all the procs in the system exceeded Sony's thermal threshholds? What if the extra hardware raises production costs and thus retail costs go up? I'd rather have the PS3 performance that Sony promised last E3 for $400 than a b/c PS3 that is only equal or less powerful graphically than the Xbox 360 (and costs $100 more).

You're making some rather pessimistic and unfounded suggestions there. The idea that PS3 hardware would get a significant reduction in performance to accomodate BC seems based on nothing at all. The complexity and thus price of some devices such as RSX may go up (GS was about 42 M transitors, I think half of which was eDRAM, so including all of GS's logic would be +20M transistors to RSX) but cost to the PS3 overall is IME unlikely to be anything above the order of $10-$20 per unit. That's expensive for Sony over 100 Million units, but hardly affects the retail price. The discussion on costs of BC on PS3 have been had on this forum before, I'm sure, and it's clear a whole system shouldn't really be needed. Some GS like functionality on RSX and hardware support for emulating the eDRAM, and a the rest should hopefully be emulated on Cell okay. The investment in design could be a lot of effort, but additional costs and impact to PS3 should be minimal. For those of us who like the idea of BC (and playing old games from outdated hardware is pretty popular), especially when it improves on the original experience, it's definitely worth it.

As for BC on XB360, I'm of the opinion that if you don't do it right, you may as well not bother. Halo and Halo2 have been, it seems, the key reason for BC on XB360, given the prominence of this on XB360 Live! gaming. But to me, it'd have been cheaper and easier to not try to offer BC but create XB360 versions of games that are popular. In this case, recreate Halo2 for XB360 with improved visuals for launch until Halo3 comes along. It could even be provided free with the system to help it as a system seller, or have it need the original discs to play and load assets. As it is now MS have a time consuming job trying to get games to work, most of which won't be played by the time they are supported.

 

[one]

I can't wait to see what sacrifices (if any) Sony made to include b/c in the PS3. IMHO, a console manufacturer has to make too many other sacrifices for backwards compatibility to cause another one. For example, if the RSX has to have trannies stripped so that Sony could put some type of hardware PS2 support in it, then I will be a bit miffed and you should be too. What if the RSX clockspeed has to be dropped because all the procs in the system exceeded Sony's thermal threshholds? What if the extra hardware raises production costs and thus retail costs go up? I'd rather have the PS3 performance that Sony promised last E3 for $400 than a b/c PS3 that is only equal or less powerful graphically than the Xbox 360 (and costs $100 more).

If you don't care about financial aspects, BC hardware can be a plus in terms of machine power. The IOP in PS2 can be used for tasks that are neither I/O nor BC. Likewise, PS2 emulation requirements may have brought PS3 some performance premium such as broader bandwidth that would not be present if they didn't bother with BC.

It's very natural that they care about BC just like Intel and AMD stick to x86 by extending it to protect their vested interests.

 

[Alpha_Spartan]

It's a mess on (a) console, but usually it works fine, and is welcome.

You can't respond to one sentence as if it is the main point of my post, because it's not. B/C is a mess on all consoles if sacrifices have to be made to include it. I doubt that b/c is a CONVENIENCE to Sony with the PS3 as it was with the PS2. It's more convenient in Nintendo's case though. I don't know whether or not Nintendo went the route that they went because of b/c or maybe they were just cheap and b/c came as a "free" perk.

Cost, probably. Kutaragi has mooted that it is expensive for them to do BC "because of the hardware", but they want to do it right from the start.

I understand that, but my point was that if a console manufacturer has to make tough hardware decisions based off of backwards compatibility, then that's a stupid route for a feature that won't get much use. Seriously, Titanio, do you actually believe that even .5% of PS3 owners will play PSX games? Why should the other 95.5% of potential customers get shafted because of a feature that only looks good on paper?

Plus there is some potential benefit to the bottom lines of companies implementing BC, with the opportunity for re-selling older games on the new systems over the net.

Is the potential revenue worth the sacrifices. Hardware b/c automatically equals sacrifices in most cases. In Microsoft's case, they had to purchase an entire company just to make sure that five people can play Halo.

 

[Alpha_Spartan]

Why on earth should that happen? Thinking that Sony would trade off performance on PS3 games just to accommodate PS1/2 compatibility is pushing it a little bit. Sony can very well accommodate what is needed without taking things off the PS3 hardware, as has been speculated here.
If PS3 will only be equal or even less powerful than X360, it certainly won't be because of BC. And if for some strange reason it is, then Sony will need to be spanked hard.

We'll see. In the perfect world, everything would come for free.

Well that's just your opinion. I can't wait to play my PS2 games like SOTC and some others at 720p with AA - if Sony keep their promises of course...
Some PS2 games looked very good, the only thing keeping them from looking fantastic was the awful IQ at times. Fix that and i'll be happy to play them again for a bit until big PS3 games come out. And i'm sure millions of people think the same.

...or they could wait until the BIG PS3 games come out before they purchase as PS3 unless they really want a cheap BD player. Hell, they may even benefit from a price drop.

 

[BlueTsunami]

I understand that, but my point was that if a console manufacturer has to make tough hardware decisions based off of backwards compatibility, then that's a stupid route for a feature that won't get much use. Seriously, Titanio, do you actually believe that even .5% of PS3 owners will play PSX games? Why should the other 95.5% of potential customers get shafted because of a feature that only looks good on paper?

The tough hardware decisions seems to be coming from the BC of the PS2 not the PSX. The PSX is soon going to be emulated on the PSP so I doubt that emulation of the PSX is giving them these tough hardare decisions.

The PS2 on the other hand is important, simply because you've got high profile PS2 games that are coming out during and soon after the release of the PS3 (one being Final Fantasy XII in the US). Also, people (like me) go back to playing old games. I just recently played an old PSX game on my PS2. Does this apply to other people? I don't know but Sony thinks its important enought to impliment.

 

[NRP]

In Microsoft's case, they had to purchase an entire company just to make sure that five people can play Halo.

I play Halo 2 on my 360 all the time. It works fine, and looks noticeably better than it did on the Xbox. So there's one of your five.

I don't think it's fair for you guys to say BC is a "mess" on the 360. A lot of the really good Xbox titles are supported. Certainly not all, but a lot of good ones are. Besides, since MS is using a software solution for BC, it doesn't seem the hardware was compromised at all. I'm actually surprised that they were able to support as many games as they already have, given that the cpu and gpu architectures are so different. As far as I'm concerned, MS has made good on their promise of BC.

 

[Shifty Geezer]

Is the potential revenue worth the sacrifices. Hardware b/c automatically equals sacrifices in most cases. In Microsoft's case, they had to purchase an entire company just to make sure that five people can play Halo.

I think you need to come up with better reasoning as to the sacrifices you think Sony have to make. Your previous examples, as I pointed out, don't to bare up under a little scrutiny. If you want to make a point that sacrifices are big, and Sony are really being hit hard including it, and end users are getting shafted with a crippled next-gen console being held back by needing to implement older hardware, you ought to give some estimates of what's being reduced and why. Like, how would RSX need to be cut back to incorporate PS2 BC? Why would clockspeeds need to be reduced to accomodate BC chips versus non-BC chips?

 

[patsu]

Looking at my hardcore gamer friends, they all have a pool of bought but unplayed games they want to get to. These are all well-known and great games, but there is little time available. B/C allow them to continue to buy existing games without worrying about their future, and also makes it easier for them to continue with the new console (Fewer switcher to other platforms). Looking at their crazy game spending habits, these small group of gamers also buy more than any others. I would want to serve them well.

From another angle, I think B/C is great for the publishers and developers. They would be appreciative of Sony's and Nintendo's extra effort to help them maintain "back catalog" sales. These sales should not affect new games sales so it's additional income for them.

In any case even as a casual gamer, I still play old games once every 1-2 weeks (sometimes every day when I'm on a roll). It's just one of those habits. One of the first things I would do when I get a PS3 is to run through all my old games quickly. it makes me happy about my PS3 purchase decision because I get instant utility without spending a single dollar more. I can be more patient about launch game draught.

Nintendo went beyond this using the virtual console route. MS also felt compelled to address Halo B/C. Unfortunately they had to do it in a round about way due to holes in the existing contracts.

In my view, B/C is not a small issue, it's a strategic and long-term advantage. It taps into Nintendo's, Sony's and the gamers' deep, common history. Microsoft will need to play its game differently since it is still relatively young in this department.

However whatever MS learned to maintain Xbox B/C at this point (Software B/C) would serve them well when they launch XBox 720.

 

[Titanio]

You can't respond to one sentence as if it is the main point of my post, because it's not. B/C is a mess on all consoles if sacrifices have to be made to include it. I doubt that b/c is a CONVENIENCE to Sony with the PS3 as it was with the PS2. It's more convenient in Nintendo's case though. I don't know whether or not Nintendo went the route that they went because of b/c or maybe they were just cheap and b/c came as a "free" perk.

I understand that, but my point was that if a console manufacturer has to make tough hardware decisions based off of backwards compatibility, then that's a stupid route for a feature that won't get much use. Seriously, Titanio, do you actually believe that even .5% of PS3 owners will play PSX games? Why should the other 95.5% of potential customers get shafted because of a feature that only looks good on paper?

Is the potential revenue worth the sacrifices. Hardware b/c automatically equals sacrifices in most cases. In Microsoft's case, they had to purchase an entire company just to make sure that five people can play Halo.

There's no reason to think that sacrifices have to be made elsewhere in the product, though, which is how it would affect me. You seem to keep indicating that, with no real information to back that up.

I'd say there's a good chance more than 0.5% of PS3 owners will at some point play a PSone game on their PS3, particularly if PSone games are made available to download. There'll be a lot of PS3 owners who never had a PSone, and they may wish to check a couple of games out from series they currently enjoy. Besides, PSone emulation will likely be a software thing, and something they can probably do fairly readily. Why not?