[TUHS] pre-more pager?

Noel Chiappa jnc at mercury.lcs.mit.edu
Thu Nov 9 06:02:22 AEST 2017


    > From: Jon Forrest

    > In the early days of Unix I was told that it wasn't practical to write a
    > pager because such a thing would have to run in raw mode in order to
    > process single letter commands, such as the space character for going on
    > to the next page. Since raw mode introduced a significant amount of
    > overhead on already overtaxed machines, it was considered an anti-social
    > thing to do.

Something sounds odd here.

One could have written a pager which used 'Return' for each new page, and run
it in cooked mode and not used any less cycles (in fact, more, IIRC the
cooked/raw differences in handling in the TTY driver).

But that's all second-order effects anyway. If one were using a serial line
hooked up to a DZ (and those were common - DH's were _much_ more expensive, so
poor places like my lab at MIT used DZ's), then _every character printed_
caused an interrupt. So the overhead from printing each screen-ful of text was
orders of magnitude greater than the overhead of the user's input to get the
next screen.

    > IIRC later versions of Unix added the ability to respond to a specific
    > list of single characters without going into raw mode. Of course, that
    > didn't help when full-screen editors like vi and the Rand editor came
    > out.

Overhead was definitely an issue with EMACS on Multics, where waking up a
process on each character of input was significant. I think Bernie's Multics
EMACS document discusses this. I'm pretty sure they used the Telnet RCTE
option to try and minimize the overhead.

       Noel


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