When a user employs a computer terminal, their input is received by the terminal and processed by a computer. The most important part of the command's route is from keyboard to electronics. Once it is entered into the terminal, it is sent electronically to a processor that then relays data through the proper channels for processing and display on screen or printer.


Input and Output Devices


The computer terminal is composed of three major components: input, processing-output, and display devices. The two most important devices used for data entry are the keyboard and pointing devices. The pointing device can generate movement on text or graphics displayed on a cathode ray tube (CRT), liquid crystal display (LCD), or plasma screen. This is done with a physical device such as a mouse, joystick, or stylus.


The primary device used to provide output is the CRT display. The CRT uses an electron gun to project images onto the screen using a focused beam of electrons. Liquid crystal displays work in much the same way but do not emit light. They consist of a liquid crystal material sandwiched between two transparent plates. A polarizing filter is placed on either side, resulting in a display that can be viewed easily in direct sunlight. An LCD monitor has greater resolution than an equivalent CRT screen and also takes up less space. The trend toward using LCDs continues to increase in popularity as they steadily drop in price.


Presentation Output


Another popular output device used with the computer system is the printer. Printer technology dates back to when early movable type printing was adapted for use with typewriters, adding the power of duplication to word processing systems. There are many types of printers available today, including thermal, dot matrix, laser, and inkjet technology. Thermal printers use the heat generated by the thermal line to transfer ink from a ribbon onto paper. Dot-matrix printers use an inked ribbon and printhead to impact the paper. The laser printer works by projecting a beam of light onto a charged drum or belt that runs between two rollers. The charged areas on the drum attract toner powder, leaving only non-charged areas exposed to create images. Inkjet technology uses small jets of ink sprayed at very high speed across a page with up to 600 dots per inch (dpi) using cartridges that attach directly to the printer body.


Terminal Isolation


In a computer terminal, the keyboard and pointing device are directly connected to the computer. The only component that is not attached to the processor in a "hardwired" fashion is the monitor. Other devices used in conjunction with a terminal include external modems, communication equipment, or speakers. External modems enable users to connect remotely from one location to another over telephone lines using various protocols such as RS-232C/V.42 bis. Communication equipment enables the user to send and receive information over radio waves instead of wire connections. Speakers provide an audio output for multimedia applications or other purposes such as providing feedback upon completion of a task.


Computer Terminal vs Personal Computer


When comparing a computer terminal with a PC, it is important to understand that a terminal is like the "thin client" of a PC and can be used as a stand-alone system, whereas a PC is designed to be part of an overall network. There are several applications where it is possible for some functions on a computer terminal to be achieved using applications through some type of remote access. This would include such activities as printing or transferring files between computers.


The trend toward networking systems has led many users away from having multiple terminals and toward buying just one more powerful machine. Terminals were initially compact devices limited by memory and processing power needed for input and output capabilities. PCs today have high-speed microprocessors with more than enough memory and storage capacity for data processing, text entry, and display presentation capabilities.


The same trend has made the development of SCADA systems possible that incorporate more PCs into a network rather than using multiple terminals. In these cases, the PC provides the necessary processing power to run an application while also controlling I/O from either serial or parallel devices. There are many reasons for this change in computer system design, chief among them is a tremendous decrease in terminal cost and an even greater increase in PC capabilities.


Conclusion

 

In the past, terminal systems were needed to provide a user with input and output abilities in places where communication with a central host was not possible. As technology has advanced, however, it is now possible for many terminals to become nodes on a network while also providing some computing power on their own. The trend toward networking computers and integrating them into an overall system has created new opportunities for terminals and has made some functions more efficient than they once were when using multiple devices spread out across one or more sites.