Computer terminal

Today, users generally interact with a server over high-speed networks using a Web browser and other network-enabled GUI applications.

Some terminals, such as the ASR Teletype models, included a paper tape reader and punch which could record output such as a program listing.

It faded away after 1980 under pressure from video display units (VDUs), with the last revision (the DECwriter IV of 1982) abandoning the classic teletypewriter form for one more resembling a desktop printer.

This reflects the fact that early character-mode terminals were often deployed to replace teletype machines as a way to reduce operating costs.

The next generation of VDUs went beyond teletype emulation with an addressable cursor that gave them the ability to paint two-dimensional displays on the screen.

The classic era of the VDU began in the early 1970s and was closely intertwined with the rise of time sharing computers.

These devices used no complicated CPU, instead relying on individual logic gates, LSI chips, or microprocessors such as the Intel 8080.

This made them inexpensive and they quickly became extremely popular input-output devices on many types of computer system, often replacing earlier and more expensive printing terminals.

The great majority of terminals were monochrome, manufacturers variously offering green, white or amber and sometimes blue screen phosphors.

By the time cathode-ray tubes on PCs were replaced by flatscreens after the year 2000, the hardware computer terminal was nearly obsolete.

Connection to the mainframe computer or terminal server is achieved via RS-232 serial links, Ethernet or other proprietary protocols.

Some Unix-like operating systems such as Linux and FreeBSD have virtual consoles to provide several text terminals on a single computer.

For other operations, there are special escape sequences, control characters and termios functions that a program can use, most easily via a library such as ncurses.

In order to overcome this, special libraries (such as curses) have been created, together with terminal description databases, such as Termcap and Terminfo.

The IBM 3270 is perhaps the most familiar implementation of a block-oriented display terminal,[18] but most mainframe computer manufacturers and several other companies produced them.

They also appear more responsive to the user, especially over slow connections, since editing within a field is done locally rather than depending on echoing from the host system.

Programmers of block-oriented terminals often used the technique of storing context information for the transaction in progress on the screen, possibly in a hidden field, rather than depending on a running program to keep track of status.

A vector-mode display directly draws lines on the face of a cathode-ray tube under control of the host computer system.

Practically all modern graphic displays are raster-mode, descended from the picture scanning techniques used for television, in which the visual elements are a rectangular array of pixels.

[citation needed] A thin client typically uses a protocol such as X11 for Unix terminals, or RDP for Microsoft Windows.

[clarification needed] In the early 1990s, an industry consortium attempted to define a standard, AlphaWindows, that would allow a single CRT screen to implement multiple windows, each of which was to behave as a distinct terminal.

Unfortunately, like I2O, this suffered from being run as a closed standard: non-members were unable to obtain even minimal information and there was no realistic way a small company or independent developer could join the consortium.

In fact, the instruction design for the Intel 8008 was originally conceived at Computer Terminal Corporation as the processor for the Datapoint 2200.

Some dumb terminals had been able to respond to a few escape sequences without needing microprocessors: they used multiple printed circuit boards with many integrated circuits; the single factor that classed a terminal as "intelligent" was its ability to process user-input within the terminal—not interrupting the main computer at each keystroke—and send a block of data at a time (for example: when the user has finished a whole field or form).

Common early uses of local processing power included features that had little to do with off-loading data processing from the host computer but added useful features such as printing to a local printer, buffered serial data transmission and serial handshaking (to accommodate higher serial transfer speeds), and more sophisticated character attributes for the display, as well as the ability to switch emulation modes to mimic competitor's models, that became increasingly important selling features during the 1980s especially, when buyers could mix and match different suppliers' equipment to a greater extent than before.

Frequently emulated terminal types included: The ANSI X3.64 escape code standard produced uniformity to some extent, but significant differences remained.

For example, the VT100, Heathkit H19 in ANSI mode, Televideo 970, Data General D460, and Qume QVT-108 terminals all followed the ANSI standard, yet differences might exist in codes from function keys, what character attributes were available, block-sending of fields within forms, "foreign" character facilities, and handling of printers connected to the back of the screen.

Large midrange systems, e.g. those from Sun Microsystems, Hewlett-Packard and IBM,[citation needed] still use serial consoles.

In recent years, KVM/IP devices have become available that allow a remote computer to view the video output and send keyboard input via any TCP/IP network and therefore the Internet.

Terminals can operate in various modes, relating to when they send input typed by the user on the keyboard to the receiving system (whatever that may be): There is a distinction between the return and the ↵ Enter keys.