Block-oriented terminal

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IBM 3279 Color Display Terminal

A block-oriented terminal or block mode terminal is a type of computer terminal that communicates with its host in blocks of data, as opposed to a character-oriented terminal that communicates with its host one character at a time. The IBM 3270 is perhaps the most familiar implementation of a block-oriented terminal, but most mainframe computer manufacturers and several other companies produced them.

In a typical application the host sends the terminal a preformatted panel containing both static data and fields into which data may be entered. The terminal operator keys data, such as updates in a database entry, into the appropriate fields. When entry is complete a block of data, usually just the data entered by the operator, is sent to the host in one transmission.

Block-oriented terminals have the advantage of causing less system load on the host and less network traffic than character-oriented terminals. On a multi-drop line there is considerable overhead for each transmission which is the same for a single character as for thousands of characters. Block-oriented terminals may also appear more responsive to the user, especially over slow connections, since editing within a field is done locally on the terminal itself rather than depending on echoing from the host system.

Early terminals had limited editing capabilities – 3270 terminals, for example, only offered the ability to check data entered into a field defined as numeric.[1] Later so-called "smart" or "intelligent" terminals incorporated microprocessors and supported more local processing.

Common block oriented terminals[edit]

See also[edit]


  1. ^ IBM Corporation (1972). IBM 3270 Information Display System Component Description (PDF). 
  2. ^ "Already over 80,000 winners out there! (advertisement)". Computerworld. January 18, 1982. Retrieved November 27, 2012. 
  3. ^ "HP 3000s, IBM CPUs Get On-Line Link". Computerworld. March 24, 1980. Retrieved November 27, 2012. 
  4. ^ Lear Siegler Inc. "The ADM-31. A terminal far too smart to be considered Dumb" (PDF). Retrieved November 27, 2012.