Microsoft Specific Google Search

Did you know that Google has a specific search function that only searches Microsoft related websites for the information?
I’m guessing the functionality works similar to Rollyo, in that they’ve picked a group of sites that focus on Microsoft information and search for your request among this specific group.
What I’m not able to figure out is what sites are searched. I’m wondering how you get your site listed in that group?
Google has other specific search sites for:

UPDATE: Microsoft
U.S. Government
Linux
BSD
Apple Macintosh