There are many ways that you can access a UNIX system. The main mode of access to a UNIX machine is through a terminal, which usually includes a keyboard, and a video monitor. For each terminal connected to the UNIX system, the kernel runs a process called a tty that accepts input from the terminal, and sends output to the terminal. Tty processes are general programs, and must be told the capabilities of the terminal in order to correctly read from, and write to, the terminal. If the tty process receives incorrect information about the terminal type, unexpected results can occur.
Every UNIX system has a main console that is connected directly to the machine. The console is a special type of terminal that is recognized when the system is started. Some UNIX system operations must be performed at the console.
Some terminals are referred to as "dumb" terminals because they have only the minimum amount of power required to send characters as input to the UNIX system, and receive characters as output from the UNIX system.
Personal computers are often used to emulate dumb terminals, so that they can be connected to a UNIX system.
Dumb terminals can be connected directly to a UNIX machine, or may be connected remotely, through a modem or a terminal server.
Other terminals, like the X terminal, can interact with the UNIX
system at a higher level. Such terminals have enough on-board memory and
processing power to support graphical interfaces. The interaction between
these types of terminals and a UNIX system can go beyond simple characters
to include icons, windows, menus, and mouse actions.