1 Jan
2015
1 Jan
'15
5:21 p.m.
On 2015-01-01 17:11, Mary Ann Horton<mah(a)mhorton.net> wrote:
The move was from termcap to terminfo. Termlib was the library for termcap.
Doh! Thanks for the correction. Finger fart.
There were two problems with termcap. One was that
the two-character
name space was running out of room, and the codes were becoming less and
less mnemonic.
Ah. Yes, that could definitely be a problem.
But the big motivator was performance. Reading in a
termcap entry from
/etc/termcap was terribly slow. First you had to scan all the way
through the (ever-growing) termcap file to find the correct entry. Once
you had it, every tgetstr (etc) had to scan from the beginning of the
entry, so starting up a program like vi involved quadratic performance
(time grew as the square of the length of the termcap entry.) The VAX
11/780 was a 1 MIPS processor (about the same as a 1 MHz Pentium) and
was shared among dozens of timesharing users, and some of the other
machines of the day (750 and 730 Vaxen, PDP-11, etc.) were even slower.
It took forever to start up vi or more or any of the termcap-based
programs people were using a lot.
Hum. That seems like it would be more of an implementation issue. Why
wouldn't you just cache all the entries for the terminal once and for
all? terminfo never came to 16-bit systems anyway, so we're talking
about systems with plenty of memory. Caching the terminal information
would not be a big memory cost.
Thanks for the insight.
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt(a)softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
1 Jan
1 Jan
6:04 p.m.
New subject: termcap vs terminfo (was: I swear! I rtfm'ed)
On Jan 1, 2015, at 9:21 AM, Johnny Billquist
<bqt(a)update.uu.se> wrote:
On 2015-01-01 17:11, Mary Ann Horton<mah(a)mhorton.net> wrote:
BSD solved this problem that way: parse /etc/termcap and put all the entries into
termcap.db. :)
Warner
The move was from termcap to terminfo. Termlib was the library for termcap.
Doh! Thanks for the correction. Finger fart.
There were two problems with termcap. One was
that the two-character
name space was running out of room, and the codes were becoming less and
less mnemonic.
Ah. Yes, that could definitely be a problem.
But the big motivator was performance. Reading
in a termcap entry from
/etc/termcap was terribly slow. First you had to scan all the way
through the (ever-growing) termcap file to find the correct entry. Once
you had it, every tgetstr (etc) had to scan from the beginning of the
entry, so starting up a program like vi involved quadratic performance
(time grew as the square of the length of the termcap entry.) The VAX
11/780 was a 1 MIPS processor (about the same as a 1 MHz Pentium) and
was shared among dozens of timesharing users, and some of the other
machines of the day (750 and 730 Vaxen, PDP-11, etc.) were even slower.
It took forever to start up vi or more or any of the termcap-based
programs people were using a lot.
Hum. That seems like it would be more of an implementation issue. Why wouldn't you
just cache all the entries for the terminal once and for all? terminfo never came to
16-bit systems anyway, so we're talking about systems with plenty of memory. Caching
the terminal information would not be a big memory cost. 
2 Jan
2 Jan
2:50 a.m.
New subject: termcap vs terminfo (was: I swear! I rtfm'ed)
Quoting Warner Losh <imp(a)bsdimp.com>:
BSD solved this problem that way: parse /etc/termcap and put all the
entries into termcap.db. :)
That's essentially what terminfo's binary files are: a parsed, cached
version of the source.
But the big motivator was performance. Reading
in a termcap entry from
/etc/termcap was terribly slow. First you had to scan all the way
through the (ever-growing) termcap file to find the correct entry. Once
you had it, every tgetstr (etc) had to scan from the beginning of the
entry, so starting up a program like vi involved quadratic performance
(time grew as the square of the length of the termcap entry.) The VAX
11/780 was a 1 MIPS processor (about the same as a 1 MHz Pentium) and
was shared among dozens of timesharing users, and some of the other
machines of the day (750 and 730 Vaxen, PDP-11, etc.) were even slower.
It took forever to start up vi or more or any of the termcap-based
programs people were using a lot.
Hum. That seems like it would be more of an implementation issue.
Why wouldn't you just cache all the entries for the terminal once
and for all? terminfo never came to 16-bit systems anyway, so we're
talking about systems with plenty of memory. Caching the terminal
information would not be a big memory cost. 
8:13 p.m.
New subject: termcap vs terminfo (was: I swear! I rtfm'ed)
"terminfo" - that was the name I was reaching for and couldn't
quite remember (and google-fu failed me)!
The other BSD answer to the "searching /etc/termcap takes too long"
problem (and I recall it being noticeable on the heavily loaded
Cory Hall PDP-11/70 when you used a terminal whose entry was farther
from the top of the termcap file) was to put the termcap entry for
your terminal into the TERMCAP environment variable at login time,
which my .login does to this day - that puts it already in RAM,
ready to go, no banging on the disk required - you only pay for
the /etc/termcap (or, excuse me, /usr/share/misc/termcap in NetBSD
5 - it seems NetBSD 6 finally moved to a BSD-ified terminfo and I
should probably update my .login ...) search once.
Erik <fair(a)netbsd.org>
5 Jan
5 Jan
8:06 a.m.
New subject: termcap vs terminfo (was: I swear! I rtfm'ed)
On 2015-Jan-02 11:13:28 -0800, "Erik E. Fair" <fair-tuhs(a)netbsd.org>
wrote:
your terminal into the TERMCAP environment variable at
login time,
which my .login does to this day - that puts it already in RAM,
But you pay for the size of $TERMCAP in every process you run.
--
Peter Jeremy
6 Jan
6 Jan
1:40 a.m.
New subject: termcap vs terminfo (was: I swear! I rtfm'ed)
Peter Jeremy scripsit:
But you pay for the size of $TERMCAP in every process
you run.
A single termcap line doesn't cost that much, less than a KB in most cases.
--
John Cowan http://www.ccil.org/~cowan cowan(a)ccil.org
May the hair on your toes never fall out! --Thorin Oakenshield (to Bilbo)
1:22 p.m.
New subject: termcap vs terminfo (was: I swear! I rtfm'ed)
Peter Jeremy scripsit:
> But you pay for the size of $TERMCAP in every process you run.
John Cowan <cowan(a)mercury.ccil.org> wrote:
A single termcap line doesn't cost that much,
less than a KB in most cases.
In 1981 terms, this has more weight. On a non-split I/D PDP-11 you only
have 32KB to start with. (The discussion a few weeks ago about cutting
yacc down to size comes to mind...)
On a Vax with 2 Meg of memory, 512 bytes is a whole page, and it might
even be paged out, and BSD on the vax didn't have copy-on-write.
ISTR that the /etc/termcap file had a comment saying something like
"you should move the entries needed at your site to the top of this file."
Or am I imagining it? :-)
In short - today, sure, no problem - back then, carrying around a large
environment made more of a difference.
Thanks,
Arnold
5:02 p.m.
New subject: termcap vs terminfo
On 01/06/2015 04:22 AM, arnold(a)skeeve.com wrote:
Even with TERMCAP in the environment,
there's still that quadratic
algorithm every time vi starts up.
Peter Jeremy
scripsit:
> But you pay for the size of $TERMCAP in every process you run.
John Cowan
<cowan(a)mercury.ccil.org> wrote:
A single termcap line doesn't cost that
much, less than a KB in most cases.
In 1981 terms, this has more weight. On a
non-split I/D PDP-11 you only
have 32KB to start with. (The discussion a few weeks ago about cutting
yacc down to size comes to mind...)
On a Vax with 2 Meg of memory, 512 bytes is a whole page, and it might
even be paged out, and BSD on the vax didn't have copy-on-write.
ISTR that the /etc/termcap file had a comment saying something like
"you should move the entries needed at your site to the top of this file."
Or am I imagining it? :-)
In short - today, sure, no problem - back then, carrying around a large
environment made more of a difference.
Thanks,
Arnold
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6:12 p.m.
New subject: termcap vs terminfo
Mary Ann Horton <mah(a)mhorton.net> wrote:
Even with TERMCAP in the environment, there's
still that quadratic
algorithm every time vi starts up.
Please remind me which one you're talking about? If TERMCAP is
in the environment there's no need to hit /etc/termcap at all.
Or are you talking about something else?
Thanks,
Arnold
5:32 p.m.
New subject: termcap vs terminfo (was: I swear! I rtfm'ed)
On Jan 6, 2015, at 5:22 AM, arnold(a)skeeve.com wrote:
No, you aren’t. And iirc, we moved the HP terminal entries to the
top of ours since we got a VAX 11/750, but a bunch of HP terminals
instead of DEC ones for reasons that likely involved graft and fraud
in the procurement office :)
Warner
Peter Jeremy scripsit:
> But you pay for the size of $TERMCAP in every process you run.
John Cowan <cowan(a)mercury.ccil.org> wrote:
A single termcap line doesn't cost that
much, less than a KB in most cases.
In 1981 terms, this has more weight. On a non-split I/D PDP-11 you only
have 32KB to start with. (The discussion a few weeks ago about cutting
yacc down to size comes to mind...)
On a Vax with 2 Meg of memory, 512 bytes is a whole page, and it might
even be paged out, and BSD on the vax didn't have copy-on-write.
ISTR that the /etc/termcap file had a comment saying something like
"you should move the entries needed at your site to the top of this file."
Or am I imagining it? :-) 
8:57 p.m.
New subject: pdp11 UNIX memory allocation. Was: termcap vs terminfo (was: I swear! I rtfm'ed)
Bringing a conversation back online.
On Jan 6, 2015, at 6:22 AM, arnold(a)skeeve.com wrote:
(Or even earlier than ’81.) How did pdp11 UNIXes handle per process memory? It’s suggested
above that there was a 50-50 split of the 64KB address space between instructions and
data. My own recollection is that you got any combination of instruction and data space
that was <64KB. This would also be subject to limits of pdp11 memory management unit.
Anyone have a definitive answer or pointer to appropriate man page or source code?
Thanks,
Milo
Peter Jeremy
scripsit:
> But you pay for the size of $TERMCAP in every process you run.
John Cowan <cowan(a)mercury.ccil.org> wrote:
A single termcap line doesn't cost that
much, less than a KB in most cases.
In 1981 terms, this has more weight. On a non-split I/D PDP-11 you only
have 32KB to start with. (The discussion a few weeks ago about cutting
yacc down to size comes to mind…) 
9:01 p.m.
New subject: pdp11 UNIX memory allocation. Was: termcap vs terminfo (was: I swear! I rtfm'ed)
Depends the processor. For the 11/45 class processors, you had a 17th
address bit, which was the I/D choice. For the 11/40 class you shared the
instructions and data space. So you had to use overlays and thunks at lot
sooner.
On Tue, Jan 6, 2015 at 2:57 PM, Milo Velimirović <milov(a)cs.uwlax.edu> wrote:
Bringing a conversation back online.
On Jan 6, 2015, at 6:22 AM, arnold(a)skeeve.com wrote:
cases.
Peter
Jeremy scripsit:
> But you pay for the size of $TERMCAP in every process you run.
John Cowan <cowan(a)mercury.ccil.org> wrote:
> A single termcap line doesn't cost that much, less than a KB in most
In 1981 terms, this has more weight. On a non-split I/D PDP-11 you only
have 32KB to start with. (The discussion a few weeks ago about cutting
yacc down to size comes to mind…)
(Or even earlier than ’81.) How did pdp11 UNIXes handle per process
memory? It’s suggested above that there was a 50-50 split of the 64KB
address space between instructions and data. My own recollection is that
you got any combination of instruction and data space that was <64KB. This
would also be subject to limits of pdp11 memory management unit.
Anyone have a definitive answer or pointer to appropriate man page or
source code?
Thanks,
Milo
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TUHS(a)minnie.tuhs.org
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2 Jan
2 Jan
9:12 p.m.
New subject: termcap vs terminfo (was: I swear! I rtfm'ed)
Warner Losh <imp(a)bsdimp.com> wrote:
|> On Jan 1, 2015, at 9:21 AM, Johnny Billquist <bqt(a)update.uu.se> wrote:
|> On 2015-01-01 17:11, Mary Ann Horton<mah(a)mhorton.net> wrote:
|>>
|>> The move was from termcap to terminfo. Termlib was the \
|>> library for termcap.
|>> But the big motivator was performance. Reading in a termcap entry from
|>> /etc/termcap was terribly slow. First you had to scan all the way
|BSD solved this problem that way: parse /etc/termcap and put \
|all the entries into termcap.db. :)
I like the current approach of FreeBSD: having a super-minimalized
version in /etc and a completely outdated (compared to the termcap
that Thomas Dickey maintains) stale version in /usr/share.
--steffen
3604
days inactive
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12 comments
10 participants
participants (10)
-
arnold＠skeeve.com -
Clem Cole -
Erik E. Fair -
John Cowan -
Johnny Billquist -
Mary Ann Horton -
Milo Velimirović -
Peter Jeremy -
Steffen Nurpmeso -
Warner Losh