Editing Computer terminal (section)

===Block-oriented terminals{{anchor|Block-oriented terminal}}===
A '''block-oriented terminal''' or '''block mode terminal''' is a type of computer terminal that communicates with its [[host (network)|host]] in blocks of data, as opposed to a [[#Character-oriented terminal|character-oriented terminal]] that communicates with its host one character at a time. A block-oriented terminal may be card-oriented, display-oriented, keyboard-display, keyboard-printer, printer or some combination.

The IBM 3270 is perhaps the most familiar implementation of a block-oriented display terminal,<ref name=IETF.3>{{cite IETF |title=TN3270 Enhancements |RFC=2355 |first=B. |last=Kelly |date=1998 |quote=3270 .. block oriented}}</ref> but most mainframe computer manufacturers and several other companies produced them. The description below is in terms of the 3270, but similar considerations apply to other types.

Block-oriented terminals typically incorporate a [[data buffer|buffer]] which stores one screen or more of data, and also stores data attributes, not only indicating appearance (color, brightness, blinking, etc.) but also marking 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, into the appropriate fields. When entry is complete (or ENTER or PF key pressed on 3270s), 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 <code>READ BUFFER</code> command or <code>WRITE</code> 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. They also appear more responsive to the user, especially over slow connections, since editing within a field is done locally rather than depending on [[Echo (computing)|echoing]] from the host system.

Early terminals had limited editing capabilities &ndash; 3270 terminals, for example, only could check entries as valid numerics.<ref name=CompDesc>{{cite book |author=IBM Corporation |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.

Unlike a character-oriented terminal, where typing a character into the last position of the screen usually causes the terminal to scroll down one line, entering data into the last screen position on a block-oriented terminal usually causes the cursor to ''wrap''— move to the start of the first enterable field. Programmers might "protect" the last screen position to prevent inadvertent wrap. Likewise a protected field following an enterable field might lock the keyboard and sound an audible alarm if the operator attempted to enter more data into the field than allowed.

====Common block-oriented terminals====
; Hard-copy
*[[IBM 1050]]
*[[IBM 2740]]

; Remote job entry
*[[IBM 2770]]
*[[IBM 2780]]
*[[IBM 3770]]
*[[IBM 3780]]

; Display
{{columns-list|colwidth=22em|
*[[IBM 2260]]
*[[IBM 3270]]
*[[IBM 5250]]
*[[Burroughs Corporation]] TD-830
*[[AT&T]] Dataspeed 40 (3270 clone manufactured by [[Teletype Corporation]])
*[[TeleVideo]] 912/920/925/950<ref>{{cite news|title=Already over 80,000 winners out there! (advertisement)|url=https://books.google.com/books?id=rx3ssrOcCTkC&q=%22block+mode+terminal%22&pg=RA1-PA6|access-date=November 27, 2012|newspaper=Computerworld|date=January 18, 1982}}</ref>
*[[Tandem Computers]] VT6530
*[[Hewlett-Packard]] [[HP 2640|VT2640]]<ref>{{cite news|title=HP 3000s, IBM CPUs Get On-Line Link|url=https://books.google.com/books?id=Z62ZAojaNzYC&q=%22block+mode+terminal%22&pg=PA35|access-date=November 27, 2012|newspaper=Computerworld|date=March 24, 1980}}</ref> 
*[[UNIVAC]] [[Uniscope]] series
*Digital Equipment Corporation [[VT52|VT61, VT62]]
*[[Lear Siegler]] ADM31<ref>{{cite web|last=Lear Siegler Inc.|title=The ADM-31. A terminal far too smart to be considered Dumb|url=http://archive.computerhistory.org/resources/text/LSI/LSI.ADM31.1978.102646290.pdf|access-date=November 27, 2012}}</ref> (optional)
*[[Honeywell]] VIP 7700/7760
*[[ITT Corporation]] Courier line
*[[Bull Questar]]
*[[ICL 7500 series]]
}}