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Why Xbox One Backward Compatibility Took So Long (ign.com)
A new report from IGN this morning explains why it took so long for backwards compatibility to be supported on the Xbox One. Microsoft veteran Kevin La Chapelle says the answer to the question can be found in 2015 -- the year that Phil Spencer announced backwards compatibility at Microsoft's Xbox E3 media briefing. From the report: The fan-first feature has evolved from an experiment conducted by two separate Microsoft Research teams into a service planned for Xbox One's launch -- complete with hardware hooks baked into the Durango silicon -- until the well-publicized changes to the Xbox One policies (namely, stripping out the always-online requirement for the console) forced it to be pushed to the back burner. It's obviously back for good now, and expanding into original Xbox compatibility of select titles on Xbox One (the first batch of which we announced today). Even the Xbox One X is getting involved, with a handful of Xbox 360 games getting Scorpio-powered enhancements like 10-bit color depth, anisotropic filtering, and up to 9x additional pixel counts displayed on screen. [...]
It was 2007. One of [the research] teams was working on PowerPC CPU emulation -- getting 32-bit code, which the 360 uses, to run on the 64-bit architecture that the third-generation Xbox would be using. The other team, out of Beijing, started writing a virtual GPU emulator based on the Xbox 360 GPU architecture. "These were like peanut butter and chocolate," Microsoft VP of Xbox software engineering Kareem Choudhry recalled. "[So we thought,] 'Why don't we put them both together?'" Choudhry did just that, and so the first steps to Xbox One backwards compatibility were taken, long before the console had a name or anything remotely resembling final specifications. As Durango crystallized, so too did plans for Xbox 360 compatibility on the new machine. "This was primarily a software exercise, but we enabled that by thinking ahead with hardware," Gammill explained. "We had to bake some of the backwards compatibility support into the [Xbox One] silicon." This was done back in 2011. Preliminary tests showed that support for key Xbox middleware XMA audio and texture formats was extremely taxing to do in software alone, with the former, Gammill noted, taking up two to three of the Xbox One's six CPU cores. But a SOC (system on chip) -- basically an Xbox 360 chip inside every Xbox One, similar to how Sony put PS2 hardware inside the launch-era PS3s -- would've not only been expensive, but it would've put a ceiling on what the compatibility team could do. "If we'd have gone with the 360 SOC, we likely would've landed at just parity," he said. "The goal was never just parity." So they built the XMA and texture formats into the Xbox One chipset...
It was 2007. One of [the research] teams was working on PowerPC CPU emulation -- getting 32-bit code, which the 360 uses, to run on the 64-bit architecture that the third-generation Xbox would be using. The other team, out of Beijing, started writing a virtual GPU emulator based on the Xbox 360 GPU architecture. "These were like peanut butter and chocolate," Microsoft VP of Xbox software engineering Kareem Choudhry recalled. "[So we thought,] 'Why don't we put them both together?'" Choudhry did just that, and so the first steps to Xbox One backwards compatibility were taken, long before the console had a name or anything remotely resembling final specifications. As Durango crystallized, so too did plans for Xbox 360 compatibility on the new machine. "This was primarily a software exercise, but we enabled that by thinking ahead with hardware," Gammill explained. "We had to bake some of the backwards compatibility support into the [Xbox One] silicon." This was done back in 2011. Preliminary tests showed that support for key Xbox middleware XMA audio and texture formats was extremely taxing to do in software alone, with the former, Gammill noted, taking up two to three of the Xbox One's six CPU cores. But a SOC (system on chip) -- basically an Xbox 360 chip inside every Xbox One, similar to how Sony put PS2 hardware inside the launch-era PS3s -- would've not only been expensive, but it would've put a ceiling on what the compatibility team could do. "If we'd have gone with the 360 SOC, we likely would've landed at just parity," he said. "The goal was never just parity." So they built the XMA and texture formats into the Xbox One chipset...
Do you know where the XBox got it's name? Microsoft wanted to make a box that runs DirectX and sits on your TV. This "DirectX Box" got shortened to "XBox", which stuck as the final product name.
The very core idea driving the project was that the system would run Windows & DirectX. You're coding against high level APIs on the Xbox, and can't opt out of it. It was a key design goal to have people coding against Microsoft's APIs instead of coding to the hardware.
As for the 8 and 16 bit consoles, syscalls were irrelevant. There was no operating system on those systems. You might have had some *really* simple, common features coded into the system rom, but otherwise *all* the code was contained within the individual game. These systems only had a bare minimal amount of storage in them - just enough to store any code needed to boot the system and hand off control to the game. Including storage in the system was too expensive to have any significant amount of code built in.
(1) They did include at least some backwards compatibility in the hardware (XMA audio and the textures format) which may or may not have been necessary. (2) The whole point the GP was making was precisely that they didn't go the simple route: include sufficient hardware to do backwards compatibility. Instead, they went the mostly emulation route which almost always results in issues. Look no further than XBox backwards compatibility on the XBox 360.
So, we can commend them on their efforts to do most of it in software? Sure. We can even be impressed, even though it sounds like they're going through and making special optimizations per game because a generic emulator won't do the job. It's still not as good as the real thing. All the claims of better? I doubt it. I used to be a really big fan of emulation. And at first, it seems quite amazing. Over time, though, it's very clear that emulation has many weaknesses and even doing per game optimizing and checks is never going to be enough.
*shrug* Then again, I don't have an XBox 360 or One.