Computer terminal: Difference between revisions

Revision as of 16:49, 29 March 2019

Revision as of 15:45, 11 April 2019

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|quote=3270 .. block oriented}}</ref> but most [[mainframe computer]] manufacturers and several other companies produced them.

Block-oriented terminals typically incorporate a [[Data buffer|buffer]] which stores one screen or more of data, and also stores data attributes, indicating not only appearance (color, brightness, blinking, etc.) but also marks the data as being enterable by the terminal operator vs. ''protected'' against entry, as allowing the entry of only numeric information vs. allowing any characters, etc. In a typical application the host sends the terminal a preformatted [[Panel (computer software)|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 (or the device's buffer - 3270), into the appropriate fields. When entry is complete (or ENTER or PF key pressed on 3270's), a block of data, usually just the data entered by the operator (modified data), is sent to the host in one transmission. The 3270 terminal buffer (at the device) could be updated on a single character basis, if necessary, because of the existence of a "set buffer address order" (SBA), that usually preceded any data to be written/overwritten within the buffer. A complete buffer could also be read or replaced using the READ BUFFER command or WRITE Command (unformatted or formatted in the case of the 3270).

Block-oriented terminals cause less [[Load (computing)|system load]] on the host and less network traffic than character-oriented terminals.

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|title=IBM 3270 Information Display System Component Description

|year=1972 |url=http://www.bitsavers.org/pdf/ibm/3270/GA27-2749-1_IBM_3270_Information_Display_System_Component_Description_Jun72.pdf}}</ref> Subsequent "smart" or "intelligent" terminals incorporated microprocessors and supported more local processing.

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. This was the precursor of the [[HTML]] technique of storing context in the [[URL]] as data to be passed as arguments to a [[Common Gateway Interface|CGI]] program.

===Common block oriented terminals===