DigitalFoundry Discusses Xbox Backwards Compatibility

Subject: General Tech | December 3, 2017 - 04:50 PM |
Tagged: microsoft, xbox

While not directly relevant to our PC enthusiast demographic, DigitalFoundry has just published a discussion about Xbox One backwards compatibility for Xbox 360 and Original Xbox games. There will be a written post, interviewing the backwards compatibility team at Microsoft Xbox, on their website soon, but, currently, just the video (embed below) is available.

The video touches on several different topics in sort-of a stream of consciousness fashion, so it’s hard to summarize but interesting to watch. For instance, with the extra GPU power, Microsoft increases resolution by a whole-number multiple, bringing 720p to 4k with a 3x3 bump, because 1080p is exactly 1.5x 720p, and 4k is exactly 2x 1080p. This leads to a problem with certain original Xbox games. More interesting, to me, is that they can directly emulate the old Xbox 360 CPU instructions. Even though AMD’s CPU is faster than a 2005 PowerPC, the clock rate is lower, and I would have expected that to cause an issue in some algorithm that is heavily frequency-dependent.

Apparently not?

December 4, 2017 | 09:01 AM - Posted by Anonymous2 (not verified)

IPC gains between PowerPC and Jaguar likely bridged that gap.

Next step: official emulator in the Windows Store. The emulation community would love to help test and optimize vGPU profiles, etc.

Seems like it makes better business sense to sell backwards compatibles games on Windows (pure profit) than selling a console at a loss.

December 4, 2017 | 01:47 PM - Posted by quest4glory

The XBOX 360 CPU would run at 1.6 GHz (half clock) for any multithreaded code.

December 4, 2017 | 06:30 PM - Posted by Scott Michaud

Yeah, the AMD chip is definitely faster than a Xeon from ~2005. I'd just figure that at least a couple games out there would have some algorithm that is frequency-bottlenecked and just cannot be fixed with IPC improvements. That said, many algorithms make up a typical frame, so it might just not be enough to matter from a macroscopic view.

December 4, 2017 | 12:17 PM - Posted by SoftwareEcosystemCostsMoreThanHardware (not verified)

I think that the x86 PC gaming market and it's software ecosystem was more of an influnce for Microsoft to move away from PowerPC than it was the PowerPC's CPU performance being a factor. That PowerPC Variant used in the Xbox 360 had 3, SMT2 capable, PowerPC(In Order) cores and each core had 128bit FP units so that CPU could support 6 processor threads and do lots of FP math.

So it must have been less costly for Microsoft at the time to go with x86 and pull in the x86 PC titles and x86 based software as the software ecosystm can cost many times more to develop and maintain that any hardware's initial development/production can cost. The software ecosystem can cost many times over what the hardware costs as hardware costs are realtvely fixed for around 5 year periods. OS/software costs are recurring on a daily/monthly basis as drivers are fixed and new games are developed and released and the console OSs/APIs are developed and maintained.

Emulation should not be hard if the software made use of any hardware Programmable Event Timers or Real Time Clocks and that was probably provided for by Microsoft in its gaming console hardware and console OSs/APIs since the Xbox console's inception.

Microsoft whent with AMD's CMT core modules and used more modules to make up for the lack of SMT capability in AMD's pre Zen CPU Micro-archs so you get the 8 core Jaguar variants that with each core sharing some FP/other resources. So an 8 core Jaguar made up of 4 modules has the same number of processor threads as a 4 core SMT enabled processor core.

In fact, that Module CMT construction has more resources than a single SMT enabled core it's just that the cache subsystems on the AMD CMT module designs was so poor that latency issues harmed gaming performance. And the Customized Jaguar cores on the XBONE-X probably has some Zen like improvments in its cache subsystems so CMT is not all bad is just that AMD did a poor job initially with its Cache/Memory subsystems and Intel was way ahead with its Cache/Memory subsystems performance that have the lower latency that benifits gaming workloads.

Once The Current Xbox is updated to a Zen/newer based design and Vega+ graphics then I hope that by that time Microsoft will have decided to make the Xbox into a full on mini-PC like system because when that Intel NUC with the Intel CPU(And its intel integrated graphics) and the AMD semi-custom Radeon Die on the EMIB/MCM arrives, Microsoft will have some very potent competition for the console/HTPC market.

I do not think that IBM was interested at the time with going along any fruther in a low margin hardware business with its PowerPC/Microsoft console variant business. And that AMD had the better hardware deal and Microsoft had it's expansive x86 OS/API/DX## graphics API software ecosystem that it was already maintaining on the x86 ISA so Microsoft made the choice to go with x86 ISA based gaming consloes.

December 4, 2017 | 01:07 PM - Posted by Rocky123 (not verified)

Yep I also liked the video and thanks for pointing us towards it to watch. I have always been a huge fan of emulation on the PC and have tried lots of different platforms being emulated from a Windows PC. What MS is doing here is great and it makes me almost want to go out and buy a Xbox One X since I have a vast amount of Xbox 360 games and just about as many first gen Xbox games. It would be great to replay some of them but get the boost in image quality as well.

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