Computer terminal

A computer terminal is an electronic or electromechanical hardware device that can be used for entering data into, and transcribing data from, a computer or a computing system. Most early computers only had a front panel to input or display bits and had to be connected to a terminal to print or input text through a keyboard. Teleprinters were used as early-day hard-copy terminals and predated the use of a computer screen by decades. The computer would typically transmit a line of data which would be printed on paper, and accept a line of data from a keyboard over a serial or other interface. Starting in the mid-1970s with microcomputers such as the Sphere 1, Sol-20, and Apple I, display circuitry and keyboards began to be integrated into personal and workstation computer systems, with the computer handling character generation and outputting to a CRT display such as a computer monitor or, sometimes, a consumer TV, but most larger computers continued to require terminals.

Early terminals were inexpensive devices but very slow compared to punched cards or paper tape for input; with the advent of time-sharing systems, terminals slowly pushed these older forms of interaction from the industry. Related developments were the improvement of terminal technology and the introduction of inexpensive video displays. Early Teletypes only printed out with a communications speed of only 75 baud or 10 5-bit characters per second, and by the 1970s speeds of video terminals had improved to 2400 bit/s or 9600 bit/s. Similarly, the speed of remote batch terminals had improved to 4800 bit/s at the beginning of the decade and 19.6 kbps by the end of the decade, with higher speeds possible on more expensive terminals.

The function of a terminal is typically confined to transcription and input of data; a device with significant local, programmable data-processing capability may be called a "smart terminal" or fat client. A terminal that depends on the host computer for its processing power is called a "dumb terminal" or a thin client. In the era of serial (RS-232) terminals there was a conflicting usage of the term "smart terminal" as a dumb terminal with no user-accessible local computing power but a particularly rich set of control codes for manipulating the display; this conflict was not resolved before hardware serial terminals became obsolete.

The use of terminals decreased over time as computing shifted from command line interface (CLI) to graphical user interface (GUI) and from time-sharing on large computers to personal computers and handheld devices. Today, users generally interact with a server over high-speed networks using a Web browser and other network-enabled GUI applications. Today, a terminal emulator application provides the capabilities of a physical terminal – allowing interaction with the operating system shell and other CLI applications.

The console of Konrad Zuse's Z3 had a keyboard in 1941, as did the Z4 in 1942–1945. However, these consoles could only be used to enter numeric inputs and were thus analogous to those of calculating machines; programs, commands, and other data were entered via paper tape. Both machines had a row of display lamps for results.

In 1956, the Whirlwind Mark I computer became the first computer equipped with a keyboard-printer combination with which to support direct input of data and commands and output of results. That device was a Friden Flexowriter, which would continue to serve this purpose on many other early computers well into the 1960s.

Early user terminals connected to computers were, like the Flexowriter, electromechanical teleprinters/teletypewriters (TeleTYpewriter, TTY), such as the Teletype Model 33, originally used for telegraphy; early Teletypes were typically configured as Keyboard Send-Receive (KSR) or Automatic Send-Receive (ASR). Some terminals, such as the ASR Teletype models, included a paper tape reader and punch which could record output such as a program listing. The data on the tape could be re-entered into the computer using the tape reader on the teletype, or printed to paper. Teletypes used the current loop interface that was already used in telegraphy. A less expensive Read Only (RO) configuration was available for the Teletype.

Custom-designs keyboard/printer terminals that came later included the IBM 2741 (1965) and the DECwriter (1970). Respective top speeds of teletypes, IBM 2741 and the LA30 (an early DECwriter) were 10, 15 and 30 characters per second. Although at that time "paper was king" the speed of interaction was relatively limited.