Editing Computer terminal (section)

==Modes==
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):
* Character mode ({{aka}} character-at-a-time mode): In this mode, typed input is unbuffered and sent immediately to the receiving system.{{sfn|Bolthouse|1996|p=18}}
* Line mode ({{aka}} line-at-a-time mode): In this mode, the terminal is buffered, provides a local line editing function, and sends an entire input line, after it has been locally edited, when the user presses an, e.g., {{keypress|Enter}}, {{keypress|EOB}}, key.{{sfn|Bolthouse|1996|p=18}} A so-called "line mode terminal" operates solely in this mode.{{sfn|Bangia|2010|p=324}}
* Block mode ({{aka}} screen-at-a-time mode): In this mode (also called [[#Block-oriented terminal|block-oriented]]), the terminal is buffered and provides a local full-screen data function. The user can enter input into multiple fields in a form on the screen (defined to the terminal by the receiving system), moving the cursor around the screen using keys such as [[tab key|{{keypress|tab}}]] and the [[arrow keys]] and performing editing functions locally using [[insert key|{{keypress|insert}}]], [[delete key|{{keypress|delete}}]], [[backspace key|{{keypress|backspace}}]] and so forth. The terminal sends only the completed form, consisting of all the data entered on the screen, to the receiving system when the user presses an {{keypress|enter}} key.{{sfn|Diercks|2002|p=2}}{{sfn|Gofton|1991|p=73}}{{sfn|Bolthouse|1996|p=18}}

There is a distinction between the [[return key|{{keypress|return}}]] and the [[enter key|{{keypress|enter}}]] keys. In some multiple-mode terminals, that can switch between modes, pressing the {{keypress|enter}} key when ''not'' in block mode does not do the same thing as pressing the {{keypress|return}} key. Whilst the {{keypress|return}} key will cause an input line to be sent to the host in line-at-a-time mode, the {{keypress|enter}} key will rather cause the terminal to transmit the contents of the character row where the cursor is currently positioned to the host, host-issued prompts and all.{{sfn|Diercks|2002|p=2}} Some block-mode terminals have both an {{keypress|Enter}} and local cursor moving keys such as {{keypress|Return}} and {{keypress|New Line}}.

Different computer [[operating system]]s require different degrees of mode support when terminals are used as computer terminals. The [[POSIX terminal interface]], as provided by Unix and POSIX-compliant operating systems, does not accommodate block-mode terminals at all, and only rarely requires the terminal ''itself'' to be in line-at-a-time mode, since the operating system is required to provide [[POSIX terminal interface#Canonical mode processing|canonical input mode]], where the terminal device driver in the operating system ''emulates'' local echo in the terminal, and performs line editing functions at the host end. Most usually, and especially so that the host system can support [[POSIX terminal interface#Non-canonical mode processing|non-canonical input mode]], terminals for POSIX-compliant systems are always in character-at-a-time mode. In contrast, IBM 3270 terminals connected to [[MVS]] systems are always required to be in block mode.{{sfn|Raymond|2004|p=72}}{{sfn|Burgess|1988|p=127}}{{sfn|Topham|1990|p=77}}{{sfn|Rodgers|1990|p=88–90}}