I/O components allow a computer to communicate with the outside world. Every I/O component in the computer has its own address, just like memory.
a) Keyboard is used to enter information from the user to the computer. It is not inherently connected to anything. The computer only responds to keyboard if the CPU is looking at the keyboard to see if someone had pressed a key. If the CPU isn't looking, the person can hit the keyboard all they want and nothing will happen.
b) Monitors are used to display information that the computer wishes to tell us. All monitors can show is a pattern of colored dots--monitors know nothing about letters or pictures.
c) Video controller is a board in the computer that controls the monitor. It translates the data in the video memory into symbols on the monitor. It can thus draw letters and graphs on the screen.
d) Parallel/Serial ports allow the computer to send data to and receive data from printers, modems, etc.
e) Mouse and Joystick are used to input positional information to the computer. They usually have their own ports, though the mouse often uses the serial port to connect to the computer.
f) Network Interface Card A NIC connects the computer to local area networks (LANs) like CLUNet. Networks are a high-speed method of transferring data from one computer to another.