Gulrajani recalled an incident on his first visit to Microsoft in 1989, when he was working for another company. He accidentally threw his meal plate into the trash and not one of the recycling bins all around the Redmond campus.

"The person I was visiting made me fish it out and put in in polystyrene recycling,'' he said.

It's a challenge for tech companies that encourage people to do more computing to make the green pitch, but Gulrajani also talked up Microsoft's efforts to greenify its new datacenters.

He noted that Microsoft's Quincy center uses hydroelectricity, a new center in Ireland takes advantage of the area's climate for cooling and a center in San Antonio is using wastewater for cooling and tapping into Texas windpower resources.

At its Silicon Valley offices, the company aded 2,500 solar panels generating 480 kilowatts of power -- about 12 percent of the facility's consumption.

Microsoft also added power-saving features to Windows Vista and Server 2008, and it's using a fleet of 50 Prius hybrid sedans as campus shuttles, he noted.