Computer Terminal

A computer terminal is an electromechanical hardware device that is used for entering data into a computer and displaying it. Although the first terminals were cost efficient, they were very slow compared to punched cards for input. As the technology enhanced and video displays were introduced, timesharing systems were developed and evolved to make up for any other problems. A terminal functions to display data and assist with data input.

Historically, the first terminals were electromechanical teleprinters or teletypewriters connected to computers. Printing terminals were developed next, but they were limited by the speed that they could print. By the 1970s, engineers in the computer industry began thinking about replacing punched cards with an affordable video data entry terminal. During this time, there were dozens of terminal manufacturers, such as Wyse, Hewlett Packard, and IBM. Most terminals were connected to mainframe computers and often had a green or amber colored screen. They generally communicated with the computer via a serial port or a coaxial cable. Later, “intelligent” terminals were introduced, such as the VT52 and VT100, which had the ability of interpreting escape sequences to position the cursor and control the display.

A text terminal is a serial computer interface for text entry and display. They were originally electronic computer terminals connected to computers by a serial port, but as time went on, computers came with built-in system consoles and terminal emulator programs. There are many different types of text terminals available today. The system console is a text terminal that is used to operate a computer. Many modern computers have a fitted keyboard and display for the console. Some operating systems have virtual consoles that offer several text terminals on a single computer. The basic type of application running on a text terminal is a command line interpreter, also called a shell. It prompts for commands from the user and executes each command. In a shell, most of the commands are actually small applications. Another important application type is the text editor, which takes up the entire area of display to display text documents and allows the user to edit them. Nowadays, the word processor has replaced the text editor because it has rich formatting features that the text editor does not.

Text terminals are very similar to files in that writing to the file displays the text and reading from the file produces what the user enters. For an application, the easiest way to use a terminal is to sequentially write and read text strings to and from the terminal. The output text is scrolled, so that only the last several lines are visible to the user. However, for some interactive applications this is not sufficient. One common enhancement is command line editing, which can also give access to command history. Further interactivity is provided with full-screen applications. Those applications control the screen layout in its entirety and respond to keys being pressed immediately. At times these programs can also control the color and brightness of text on the screen, and decorate it with underline, blinking and special characters.

A graphical terminal can display both images and text. Graphical terminals are divided into vector-mode terminals and raster mode terminals. A vector-mode display is under the control of the host computer system, and it draws lines directly on the face of a cathode-ray tube. The lines are endlessly formed; however, the number of concurrent lines that can be displayed at one time is limited. Although vector-mode displays were historically important, they are no longer used. Today, nearly all modern graphic displays are raster-mode, in which the visual elements are a rectangular display of pixels. Since the raster image is only visible to the human eye as a whole for a limited time, the raster must be refreshed multiple times per second to give the appearance of a constant display. Today, most terminals are graphical, which means they can show images on the screen. Since the arrival and following popularization of the personal computer, hardly any authentic hardware terminals are used to interface with computers. Modern operating systems are known to use the monitor and keyboard, which are mostly independent from the hardware used.

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