He'd scrap Windows

Instead of trying to support every application ever made for the Mac, OS X was a clean break from previous versions of the Mac OS; if you wanted to run old apps, you ran them in Classic.

"Jobs would ditch Windows' legacy code completely and rewrite it from the ground up," Barlow suggests. "Windows is a mess, and it's time to clean house."

Legacy support? Virtualisation. By starting from scratch, Windows 8 would "run fast, be rock-solid, have built-in support for the latest hardware such as USB3 and Blu-Ray, and it would cut the install footprint of Vista by 80 per cent." Best of all, "there would be no need to validate your copy by phoning up a computerised helpline. It would just work."

He'd give Windows Mobile a serious kicking

WIndows Mobile was looking pretty dated before the iPhone; now, it's an embarrassment. The same issues that hobble Windows on the desktop - legacy support, hardware firms doing whatever they want, old code - affect Windows on mobile phones, and unless Windows Mobile 7 is a ground-up rebuild - which we doubt - then Mr Jobs would can it, put the entire development team into a dungeon and refuse to let them out until they built something insanely great. He'd bring phone hardware in-house, too.

He'd fiddle with the Xbox

The Xbox 360's media features, marketplace and massive user base would be hard for Jobs to resist. Naturally, he'd change it. "He'd look at it and say that it's too noisy, that it isn't pretty enough, and he'd make it quieter and more elegant," says Enderle.

Microsoft's relationship with gaming firms could change, too. "Jobs doesn't partner well," Enderle says. "He'd probably try to reverse the Bungie spin-out… he'd say, okay, we're going to take the millions of dollars we have and buy back or buy up these gaming companies – or at least, the core guys with the major titles – and make sure they focus solely on the Xbox."

There's one slight problem. As Enderle points out, "the one thing he doesn't get is gaming. He's never been a gaming guy, so you have to wonder whether by the time he's done he'd turn it into an Apple TV and lose the very reason people buy Xboxes in the first place."

Of course the iPhone has become very successful as a mobile gaming platform, but we suspect that's happened despite Jobs' involvement rather than because of it.

There's one particular bit of gaming tech that we think Jobs would be interested in, though, and that's Project Natal, the gesture-recognising system that wowed everyone at E3.

If it's as good as Microsoft says it is, we can easily imagine Jobs taking it out of the gaming ghetto and pushing it into mainstream computing. This is, after all, the man who famously hates buttons. What better than an input device made of air?

He'd kill Microsoft

Leander Kahney is the author of Cult of Mac and Inside Steve's Brain, which explains how "a mercurial obsessive with a filthy temper" became one of the most influential people on the planet. "If Jobs were in charge at MS, he'd wreck the company and drive it into bankruptcy," he says.

As Kahney points out, Microsoft and Apple are complete opposites. "Microsoft is open, un-integrated, un-coordinated and doesn't control key technologies such as hardware. Worst of all, it's not interested in innovation and neither are its customers. Microsoft can't – and never will – innovate. It's not a good business model for the company. Microsoft copies innovative technologies on the way up as they become popular, then uses its market clout to push them mainstream. Then, it milks them."

He continues: "If Jobs did to Microsoft what he did at Apple – close it up, focus on innovative products and product categories – he'd kill Microsoft's business model (milking Windows and its desktop apps) – and drive it into the ground."

Rob Enderle agrees. "It could emerge as a very different and much smaller company, but it wouldn't be Microsoft," he says. "Microsoft is the embodiment of Bill Gates' vision, and that's exactly what Steve Jobs would change."

Would Microsoft survive those changes? "Not a chance," he laughs.

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