Microsoft's Engineering Windows 7 has a long post by Steve Sinofsky on the background to Windows' development. He lists the various groups that contribute to the project -- from Applets and Gadgets to Windows App Platform -- and says:
we create feature teams with n developers, n testers, and 1/2n program managers. This ratio is pretty constant across the team. On average a feature team is about 40 developers across the Windows 7 project.
So, 40 developers times 23 groups comes to 920 people, so the total is probably around a thousand. Assuming they cost Microsoft $100,000 per year each, that comes to $100 million a year.
It sounds like a big team, but maybe not so big if you break it down. If there are 40 people working on something like IE8 or Media Center, that means there are (following Sinofsky's formula) only 16 actual programmers on each team.
Is that too many, or too few?
IBM had over a thousand people working on OS/2, and at the time, most people reckoned that was bloated*.....
* Note: this was meant to indicate a bloated team. The code wasn't all that bloated....
