[TUHS] Line Terminators in Text Files [Was: Re: Why Pascal is Not My Favorite Programming Language - Unearthed!]

Pete Turnbull pete at dunnington.plus.com
Mon Sep 4 10:31:22 AEST 2017


On 04/09/2017 00:14, Chris Torek wrote:

> In what was either a remarkable coincidence, or actual planning,
> the old ASR 33 at I think 110 baud (maybe 300) took two "character
> times" to do the carriage return, so that if you sent CR and LF
> in that order, the LF occurred mid-CR and the print head was
> ready right at the time the next character arrived.

That's not right.  Yes, the ASR33 runs at 110 baud (10cps), but all - 
including mine and those of my friends -  take more like half a dozen 
character times to perform a CR from the right hand side.  Moreover, the 
time it takes depends in a non-linear fashionon how far along the line 
the printhead has travelled; it's driven by a spring and decelerated and 
stopped by an air dashpot.  Even an LF takes more than two character 
times.  That's why ASR33 drivers send a string of nulls after a CR. 
Many are smart enough to send the LF instead of the first null, if they 
see that LF is the first character after CR.

>> But there were also some terminals that both advanced the paper
>> and returned the print head (I'm hazy about this, but I think
>> the IBM Selectric was one...).

The ASR33 friction feed models, but not the sprocket fed ones, can be 
configured to do that but AFAIR only at the 72nd character position at 
the end of a line.

> Possibly, since as I recall there was a keyboard key that did the
> equivalent of pushing the return bar on a manual typewriter.  If
> you look at photos of Selectrics, there is no external bar (though
> of course there are knobs to rotate the platen for inserting and
> removing pages).

That's correct.  Selectrics have a RETURN key, which performs carriage 
return and linefeed, and on mine there was a switch for single/double 
line spacing too.  I no longer have one, but I used to have two.

-- 
Pete
Pete Turnbull


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