Generally communication is the process of transmitting data from one person or one device to another.
The term data communication is used particularly for transmission of data between a user and a computer or between computers .
Telecommunications are data communications over large distances.
A terminal is an input/output device that enables a user to communicate with a computer. Examples of terminals
1- A visual display unit .
2- A cash issuing terminal outside a bank .
3- A microcomputer running a program which makes it behave as a terminal.
Remote-a terminal which is a considerable distance from the computer is referred to as remote. A remote terminal is connected to the computer by the telephone system or by some other data link.
Local- a device or system is local if it is not using any remote links. Examples of uses of the terms local and remote
1- A terminal is in local mode when it is not on-line to any computer but is being used off-line.
2- A terminal is said to be a local terminal if it is connected to a local area network (see below).
3- The owner of a home computer and a modem can use the computer as a remote terminal to book a holiday via Prestel (for modem for Prestel .
An intelligent terminal is a terminal which has its own processor and can run some programs without linking to a central computer. It is also known as a programmable terminal. (Microcomputers are often used as intelligent terminals.)
Teleprocessing is processing which is carried out using a remote terminal.
In data communications a network is a system of computers and/or terminals connected together.
A work station is a terminal or a computer which an operator uses to interact with the network.
There are two main types of network:
1- A local area network (LAN) is a network in a small area, often one building. The work stations in a local area network are connected directly by cables .
2- A wide area network is a network operating over long distances. The work stations in a wide area network are connected by telephone or similar data links .
Local area network-.a network of computers in a school. Wide area network-a viewdata network .
Parallel transmission of data means that the bits for each character are all sent at the same time.
If the transmission is by cable then there is a separate wire for each bit. With an eight-bit code there are eight wires for the data.
Serial transmission of data means that the bits for each character are sent one after the other.
If a cable is used data could be transmitted along one wire.
The speed at which data is transmitted is measured in baud (named after a French engineer called Baudot ) .
For serial transmission 1 baud is 1 bit per second.
An alternative measurement is in characters per second (c.p.s.).
Serial terminals usually transmit ten bits for each character.
Thus 300 baud = 30 c.p.s.
9600 baud=960 c.p.s.
Labels: Computer