[andrewf]

Each company is different, I could be way off the mark, and 3 hours strikes me as a little short for the standard format.

A common interview format will have you doing multiple, separate interviews, usually 60 minutes long, with different people. The purpose of this is to gather a few independent opinions. You might be asked to write code, you might be asked to sketch architecture, you might be asked to tell war stories.

Try to stay relaxed, be candid, and take a break/drink/use the restroom between interviewers. Try to start with a blank state, mentally, for each round. Also, bear in mind that if you're breezing through the interview, people will often start asking tougher questions to try and figure out where your limits are. If, by the halfway mark, you're being asked things you don't know the answer to, that does not mean you're failing. (Avoid bullshitting if you reach this point, it'll be obvious and count against you, it's worse than just saying you don't know)