One of the more remarkable features of the Internet is the way it lets you use the resources of a distant computer somewhere else in the world. From your own home or office, you can log on to another computer, issue commands just as if you were at that computer's keyboard, and then gain access to all the computer's resources. You do this with an Internet resource called Telnet. Telnet follows a client/server model, which means that you run a piece of software on your own PC (the client) to use the resources of a distant server computer. This distant computer is called the host.
The host allows many clients to access its resources at the same time; it isn't devoted to a single user. To use Telnet and the host's resources, you must know the address of the Internet host whose resources you want to access.
When you use Telnet, before you can take over the resources of a host computer you typically have to log on to the host. Often, you can use the name "guest" to log on. Some systems require that you also give information about yourself, such as your name and address. And some might require that you choose a username and a password that you will use the next time you log in.
You can access many hosts on the Internet by using Telnet. They are all different computers, so many of them don't work or look alike. For example, some might be Unix-based systems, some might be Windows-based computers, and some might be Macintoshes, as well as a variety of other computers, and they all work and look different from one another. As a way to make things easier, many hosts use a menuing system that gives you access to their resources.
Telnet gives you a way to use those menuing systems by using something called terminal emulation. It lets you use your computer to emulate the type of keyboard and computer that each of the different computer systems expect. Different computers often require different kinds of terminal emulation, but one common kind is called VT-100 emulation, so if you use Telnet software and tell it to use VT-100 emulation, that's a safe emulation to use.
Telnet clients are available for all the major operating systems, including Unix, Linux, Macintosh, and all versions of Windows. If you use Unix or the Windows DOS command prompt, you'll typically use a Telnet client by simply typing the word Telnet followed by the Internet address of the computer you want to access. For example, if you wanted to gain access to a computer run by the federal government that gives access to the Library of Congress, you'd type Telnet locis.loc.gov. A Windows- or Macintosh-based Telnet client is easier to use than a DOS- or Unix-based Telnet client because the former remembers hostnames for you. With clients, you can often keep an address book of hostnames so you can easily revisit them.
Telnet is one of the oldest uses of the Internet, and is not nearly as common today as it was at one time. It is more often used by system administrators to log on to and control systems than it is used by everyday Internet users. Still, it continues to serve its purpose, and has not yet gone away.