The microcomputer uses internal communications lines in order to pass information among its components. Ports provide external connections so that devices can be connected to a computer or so that the computer can be connected to other computers. Ports (and cables) are needed for communication to flow to and from input, output, and storage devices. One can also have lines of communication to other computers or networks of computers in which case you need a modem or a NIC (Network Interface Card.) Buses and ports, modems, LANs, and WANs are all different aspects of communication and networking.
Slots can provide a mechanism for adding components to the internal bus so that you can extend the computer. So called "daughter cards" plug into slots on the "motherboard" adding to the components that one would consider internal to the system unit.
For an external hardware device, such as a keyboard or printer, to communicate with a computer it must be able to hook up to the computer. This is usually done through a plug called a port which is located at the back of the computer. There are different types of ports allowing various types of external devices, or peripherals, to connect to the computer. Click here for more details on ports and plugs.
Modems allow one computer to communicate to another computer which is not linked to it by dedicated cables and ports. Modems allows computers to use ordinary telephone lines. The modem translates digital information (such as found on a CD) to sound (analog information), and sends it over the telephone network. The modem receiving the information translates the analog information back into digital form and sends it on to the computer.
External modems, like the two pictured above, are boxes which plug into the computer through a port (typically the serial port), and into a telephone jack. An internal modem comes in the form of an expansion card and fits into a slot inside the computer's casing.
Fax modems are capable of sending and receiving information to and from a normal fax machine, as well as modem-to-modem communication.
The speed at which modems transmit data is measured in bits per second or bps. Slower modems transmit at 2400 bps or less, while faster modems can transmit at 28,800 bps.
The computers in a LAN, such as found in an office, are sometimes connected to share peripherals like expensive laser printers by their serial ports.
A network that allows the sharing of data as well as hardware, and provides an electronic means of communication between users, usually uses network interface cards or NICs rather than the standard ports. The computers each have a NIC in a slot which is then connected to a network cable strung in a particular fashion (topology) between the computers. Users can then share hardware, information, and programs over the web of cables. Often on such a network there might be a server, which is a computer dedicated to serving information and programs to the rest of the networked computers.
The Internet is probably the best known WAN. An internet is any network made by connecting two networks. The Internet is the sum of all the smaller networks connected together and using TCP/IP (Transfer Control Protocol/Internet Protocol) to exchange information.
A microcomputer needs an extra piece of hardware in order to communicate on a network. This is called a network interface card or NIC. NICs are a type of expansion card. For more details see expansion cards and slots.
Introduction to Computers
IHC - 2E03
Humanities Computing Centre