[GreenKeys] ENTER

[Jim Haynes]

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.