Computer terminal
A terminal, also referred to as the console of a computer or traditionally in the German language as a visual display unit, a user terminal for entering and displaying data.
Terminals have been developed to replace the telegraph used on mainframes until then. Today is the abbreviation tty of the English word for telegraph, teletype, ubiquitous in Unix operating systems and associated software.
While in the early days even the teletype similar devices - referred to as hardcopy terminals, consisting of a printer and a keyboard - were in use, the advantage of terminals was later that a screen for the reproduction of the data was used. Through him, could and can not only be sequentially output lines; the desired maneuverability of the cursor allows scrolling and changes of text.
The starting around 1977 gradually incipient spread of personal computers has now replaced the terminals of most offices. Many terminals have been replaced by terminal emulators that run on a PC. To date, terminals, however, are common in some areas.
Compounds
For the connection between the terminal and the computer it was on the one hand (from the Telegraph ) the serial interface in the two variants as RS- 232 interface ( standardized in EIA RS -232 or CCITT V.24) or mainly in industrial applications as a 20 - mA interface, which was standardized as DIN 66258 and had established himself in a part of the market as the de - facto standard. Other manufacturers, including market leader IBM, used proprietary interfaces.
Originally terminals were always connected directly to the computer, which had to be equipped with the corresponding number of interfaces. Later there was a wide range of solutions to connect multiple terminals on a common line, which he was commanded economically especially in the case of remote offices. IBM was able to connect on the basis of a proprietary protocol within the Systems Network Architecture terminals, DEC continued for a DDCMP.
For larger distances, but also the standardized protocol X.25 found a certain distribution.
With the introduction of local networks, for instance based on Ethernet, there was more connection options for terminals which ultimately only those who use the Internet Protocol, have prevailed. The introduction of the Internet one connection of local and remotely located terminals is imputed then become possible.
Terminals are equipped with a special functionality that is tuned to their application.
One distinguishes between text and graphic terminals. The former can represent only the letters and characters of a particular character set ( ASCII often ), in a matrix of 80 columns the most (as many as punch cards have ) to be placed, and 24, or 25 lines.
The significantly more expensive graphics terminals were primarily developed by Tektronix. They were the forerunners of the pixel-oriented hardware used today. However, there was in contrast to today vector-oriented terminal, in which the electron beam in the cathode-ray tube was free programmable. There the image is therefore not from a memory ( today: graphics card), which was very expensive, read out and transmitted line by line and pixel by pixel on the screen, but the lines were written directly onto the phosphor layer, wherein the memory only coordinates of the lines were vorzuhalten. For this purpose, most memory picture tubes were used.
In practical language use today are almost all data terminals, where users can enter something called a terminal, as well as the list of examples below shows. A pseudo-terminal is a virtual computer terminal in Unix or Linux systems for input and output of data, which allows a program control another program as if it were a user.
Examples of Terminals:
- Virtual terminals as text consoles for Unix computer
- ASCII terminals such as VT100 DEC or ADM -3A Lear Siegler
- IBM 3270 terminals
- IBM 5250 terminals for accessing IBM iSeries or IBM AS/400
- X terminal
Industry-specific terminals:
- Self-service terminals
- Electronic Cash Terminals
- POS terminals
- Terminals for data acquisition