Re: ASCII code for pc return
Re: ASCII code for pc return
- Subject: Re: ASCII code for pc return
- From: "Mark J. Reed" <email@hidden>
- Date: Fri, 22 Apr 2005 17:56:53 -0400
On 4/22/05,
Christopher Biagini <
email@hidden> wrote:
> Don't they use some wretched CRLF system? One character isn't good
> enough.
It makes a certain amount of sense, and is consistent with the original
definitions of CR and LF when the code set that would one day become
ASCII was used for sending telegrams: CR returns the carriage to the
far right (moves the cursor to the far left), while LF rolls the platen
up one stop (moves the cursor down one line). So CR by itself
will let you go back and write over the same line again, while LF by
itself is a cursor down that leaves you in the same horizontal position.
Most OSes with ASCII-based character sets opted to use a single
character to signify "end of line", which would get translated to the
CRLF sequence needed to actually display text on a teletype. This
was done to save space, which was after all at a premium on machines
with a few K of RAM and floppy disks that held only around 150K
total. Most of these OSes adopted CR by itself as the end-of-line
sentinel, but UNIX went the other way and adopted LF by itself.
This fit in with the by-now-familiar way text editors and word
processors work: you can't cursor down into text you haven't composed
yet. Given that restriction, an LF without a CR was meaningless,
while a CR without an LF (going back to the start of the line to
overwrite what was there) still made sense. So CR kept its
original semantics while LF got treated as if it always had a CR
prepended to it.
So the Mac used CR and UNIX used LF and then they begat OS X, which as
far as I can tell uses LFs underneath everything but makes them like
like CRs in the Aqua apps.
--
Mark J. Reed <
email@hidden>
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