Replying to Mac Startup Disc Help

Alright, so I run windows on my mac via bootcamp, and I constantly switch between mac and windows to do my school work. The problem is, I'm getting tired of having to hold option when I restart to select what startup disc I want to run. I've seen macs that automatically give you the option to select a disc at login/startup, but I don't know how to set that up. Does anyone know what I am talking about and how to set it up? Thanks.