expect to come face to face with something called a "shell prompt". Shell prompts look like this: % (or some other obscure symbol, like a dollar-sign) or this: mail> (a favourite--means you're in some sort of mail program) or like this: prez23: (means 23rd command since you logged into computer "prez"). A prompt means the other computer expects you to type a command for its "shell", or "command interpreter". The shell is the outer layer that you, the user, interact with. Two other types of "user interfaces" you might encounter are: o menu systems that give you choice of numbers o "window" systems or graphical user interfaces (GUIs, pronounced "gooey"). Menu systems are popular on bulletin board services, and usually present no problem to the novice. Their weakness is that they get cloying after about five minutes. Most menu systems that are designed to be used for that length of time or longer have a "command mode", where you get--you guessed it--a shell prompt. Even windowing systems (you know if you have one of these) very often give you a window that "emulates a terminal", i.e. that gives you a shell prompt inside. So, you see, in each of the three common user interfaces--command line, menu-driven, or graphical user interface--you will likely encounter, at some time in your life, a shell prompt. Advice on things that will likely work to get you started is given here and in Appendix A. Some experience of other kinds of computers, especially computers that use the UNIX operating system is useful. Some tips about using UNIX and other operating systems you may not have encountered before is given in Appendix D. If you do get stuck, whether by being experimental or just by accident, it is helpful to remember a few points: o You can always disconnect from a remote service by using your communications software to "hang up". o If the computer gives you a strange symbol like a percent sign or a dollar sign and just sits and stares at you, you can try "help" or "?" to try to find out what the computer expects, or else try "exit", "quit", "bye", "logoff", or something similar, to return to where you were before. o Many times, when you log on to a system, you will get instructions on how to get further help or how to "escape" back to your own system. You should remember these or write them down! o As a last resort, exit the communications program (and all other active programs) and shut off your computer, turn off your modem, and disconnect it from the phone line. Be sure to do these steps in the order prescribed. It is unwise (though tempting) to simply turn your computer off and on, or to pull the plug on your modem with your computer running. More suggestions for the inexperienced are given in Appendix A. The final hurdle to using the Internet is that the world, even the world of the Internet, is indeed a very large place. When using the Internet you have to decide: o where to go; o what information you want (and where it might be); and o how to get to it (and get it back home intact). For a system as vast as the Internet, these are hard decisions. Often, the only strategy that works is to explore and try different things. This course is designed to get you over the initial hurdles, give you a fair grounding in methods that work, and point you in the right direction. The exploration is up to you. As an initial orientation, we describe the "three worlds of the known Internet" in the next section.