Data stream from hardware

Hello,

I have been programing in C++ for about a year. I have written several basic programs in UNIX and also in windows using MFC. All my previous programs only had user input. What I am interested in now is to learn how one get input and output from, and to, a hardware device. Are there any fundamental functions that I could play around with that would give me access to a hardware device such as a modem or a sound card for example?
If yes, is there a list of these functions or is there a good book on the subject.

Any help would be greatly appreciated
thank you