Character-cell and block-oriented terminals
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A block-oriented terminal is a type of computer terminal that communicates with its host in blocks usually consisting of chunks of text, as contrasted with a character-oriented terminal that communicates with its host one character at a time.
With a block-oriented terminal, the terminal is sent a description of the fields on the screen by the host. The terminal then displays these fields and permits the user to edit them; when the editing operation is completed, the terminal submits the entire fields back to the host in one burst. Thus communication between terminal and host occurs in blocks of data.
By contrast, a character-oriented terminal submits each character from the terminal to the host as it is typed.
Block-oriented terminals have the advantage of causing less system load on the host and less network traffic. They are also more responsive to the user, especially over slow connections, since editing within a field is done locally on the terminal itself. This makes them especially ideal for data-entry applications.
Character-oriented terminals, on the other hand, are less complex to program, and are more powerful and general—many types of user interfaces cannot be implemented (or are difficult or clumsy to implement) with block-oriented terminals, but can be done with character-oriented terminals. Some particular examples include visual editors, command line interfaces and rogue-like games. Note however, the first two do have implementations for block-mode terminals (IBM mainframe and minicomputer CLIs and visual text editors), but they have certain limitations compared to their character-oriented cousins.
Character-oriented terminals have historically been the most common type, and include UNIX-derived systems, and most DEC systems (VT100, VMS, etc.).
The IBM 3270 and IBM 5250 are the main examples of block-oriented terminals. Although DEC systems mainly used character-oriented terminals, the VT131 and VT132 had a block mode capability.
The rise of web-based interfaces can be seen in some ways as a return to block-oriented terminals, due to their similarities; indeed, many applications today exist which will convert a block-oriented terminal stream (esp. IBM 3270) to a HTTP/HTML stream.
