[GreenKeys] ENTER

[David Christ]

The thing to remember here is that when we are talking about 3270 
series terminals and such, they operate under a whole different 
philosophy.  Teletype machines are character by character devices. 
3270 equipment was buffered and sends data in a bulk fashion.  The 
underlying architecture was SNA (Systems Network Architecture) which 
dates back 40 years when achieving 2400 baud was considered fast.  In 
essence on a 3278 or 3279 terminal your entry went into a buffer 
which was displayed on the screen.  No data was transmitted until the 
enter key was pressed.  And even then only the parts of the screen 
relevant were transmitted.  Although we programmers used these 
terminals as an upgrade from keypunches with the source decks stored 
online, the majority of the units were used for data entry.  With the 
rise of the IBM PC, the 3270 terminal disappeared but the mainframe 
did not know that.  The 3278/3279 was emulated on the PC and 
protocols such as TN3270 allowed the old programs to be used without 
change.

3270 terminals are just different kinds of beasts.  They are not the 
same thing as the glass terminals that replaced the mechanical 
teleprinter.  The 3270 series was IBM Mainframe centric.  It was a 
page by page device not character by character.  Reminds me of the 
problem many had with early word processing programs.  Those who used 
a typewriter had been trained to think in a line by line fashion. 
Every line ended in a CR/LF.  Word processors worked in a paragraph 
by paragraph fashion.  A CR/LF meant the end of a paragraph and lines 
as such did not exist except by virtue of wrap around as a function 
of the display or printing device and formatting rules.  It was not 
uncommon early on to see typists insisting on entering a CR/LF as the 
characters reached the right side of the screen.

Whether this has strayed off topic depends of the scope of Greenkeys. 
Hopefully there is a place for discussion of where teleprinters fit 
into the broader topic of communication.

David K0LUM

At 11:47 AM -0500 8/3/12, Jim Haynes wrote:
>On Fri, 3 Aug 2012, Dr. David Link wrote:
>>
>>  I was wondering if the origin of the ENTER key (as opposed to CR) was
>>  also in teletype chat?
>
>So far as I know teleprinters have always had separate CR and LF keys.
>Except of course tape printers that don't need them.  This was carried
>over into ASCII.  Then there was some discussion about why we needed two
>different keys and an addition was made that the LF character could also
>be used as NewLine NL doing both CR and LF functions.  On a
>highly-mechanical teleprinter this would have to be followed by some
>non-printing characters to give the carriage time to return.
>
>Printing terminals derived from the IBM Selectric typewriter, such as the
>2741, already did CR and LF as a single function since that's what a
>typewriter does.
>
>But neither of those is explicitly the "Enter" function, which has the
>meaning to a computer that the characters received up to this point are
>now to be delivered to the program that is waiting for them.  There is
>nothing fundamental to the idea that a CR-LF should perform the Enter
>function.  It could as well be done character-by-character, or
>word-by-word, or whenever a buffer reaches a certain state of fullness.
>
>Something about the computer system has to be responsive enough to
>receive the characters as they come in, or they will be lost.  In a
>minicomputer there is usually an interrupt as each character comes in,
>and some high-priority routine puts the character into a buffer so
>that the hardware is ready for the next character.  Then the program
>that wants the character is running at lower priority and takes one or
>more characters when it can.  Thus in modern times we expect the computer
>to react to a single character.
>
>In older systems which were batch-processing oriented the terminal
>keyboard was regarded as a particularly unruly kind of card reader.
>The charcters had to be accumulated somewhere, but the program using
>them didn't want to hear about them until it asked for them, and at
>that time it wanted a whole card full of characters to process.
>
>>
>>  Or did manual keypunches have an enter key?
>>
>No need for an enter key on a keypunch since the end of the card provides
>the enter function.  The card reader reads a whole card at a time.
>______________________________________________________________
>GreenKeys mailing list
>Home: http://mailman.qth.net/mailman/listinfo/greenkeys
>Help: http://mailman.qth.net/mmfaq.htm
>Post: mailto:GreenKeys at mailman.qth.net
>
>This list hosted by: http://www.qsl.net
>Please help support this email list: http://www.qsl.net/donate.html