When Steve Ballmer is having fun, everybody knows it.
It's not just the famously booming voice and sweatily energetic public performances. Mr Ballmer is not seen in tech circles as a "product guy" "the breed held in highest esteem â€“ but when Microsoft has something new to show off, there is no more engaged pitchman.
"He genuinely likes this stuff: he's excited by it," says Michael Cherry, a former Microsoft engineer. "He still has a sense of wonderment and awe about what the technology does."
If the Microsoft chief executive has been grinning like a child in a sweet shop of late, however, it is not just down to the arrival of Windows 8.
Nearly 12 years since taking over from Bill Gates, Mr Ballmer has finally shaped Microsoft into a company more attuned to the changing world of mobile devices and the cloud. And with this week's abrupt departure of Windows boss Steven Sinofsky, he has completed a clean-out of top management that represents a sea-change in the way the world's biggest software company is run.
For much of his first decade at the top, Mr Ballmer's Microsoft was entangled in the debacle stemming from its Windows Vista PC operating system.
As Mr Ballmer confessed this week, the repeatedly delayed Vista sucked in much of the company's top engineering talent for far too long. That stole resources and attention from mobile at a key moment, he said, leaving Microsoft badly behind in what has become the tech industry's main race for the future.
So might this week's sudden departure of Mr Sinofsky, a well-regarded engineer, cast a shadow at just the moment Mr Ballmer feels he has put Microsoft back in the game?
Mr Ballmer was having none of it.
Mr Sinofsky himself had always argued that the best time to replace a top manager is at the end of a product development cycle like this, he said â€“ adding, without apparent irony: "He's living his principles, so to speak."
With the departure, the powerful heads of the company's four biggest divisions have now all left in the past two years.
Their responsibilities, in all but one case, have been carved up between more junior executives. Ditching Microsoft's traditional cadre of divisional barons has left Mr Ballmer himself firmly in control and more fully in the spotlight.
He also now sees himself as the bulwark against any future slide into irrelevance. Tech companies need to remake themselves every five to 10 years, he said, and the impetus for change can only come from the top.
Cranking up the famous impatience, he described this week how he had prodded one group of cautious Microsoft engineers: "Let's just do it. Let's move, let's move, let's move, let's move."
Microsoft's board has shown its own impatience with its CEO of late, giving him only half of his potential bonus in each of the past three years for his handling of the transition from PCs to mobile devices.
Should Windows 8 flop, Mr Ballmer's own head may be the one on the chopping block next.