Microsoft disclosed late Thursday that Jeff Raikes, the head of its Office operation, second only to Windows in bringing in revenue, was retiring and will be replaced by Stephen Elop, 44, Jupiter Networks' short-term COO.

Before Jupiter, Elop was president of worldwide field operations at Adobe by virtue of Adobe's 2005 acquisition of Macromedia, where he was president and CEO. Elop also has experience as a chief information officer.

The plan is for Raikes, 49, to hang around until September as a backstop as a member of the senior leadership team for purposes of transition.

That's only a few weeks after Bill Gates ostensibly cleans out his desk at Microsoft and retires.

Elop, who now joins the clutch of men who might ultimately replace CEO Steve Ballmer, will start at Microsoft the end of January and pick up Raikes' responsibilities for the company's Information Worker, Business Solutions and the relatively new Cisco-bucking Unified Communications units.

He will have to deal with Office's SaaS challengers.

Bob Muglia, head of the Server and Tools business, will continue in that job but report to Ballmer.

Raikes has been with Microsoft since 1981. The Microsoft Business Division that he's run now brings in $16 billion a year.