When did the `dc' command first appear?

[wkt@cs.adfa.edu.au (Warren Toomey)]

In article by Greg Lehey:
> > There's a binary of dc from either 1st or 2nd Edition in the PUPS Archive:
> > 	-r---wxrw- 0/0            6846 Apr 14 06:50 1973 bin/dc
> 
> Wouldn't that be the Third Edition with that timestamp?  I won't
> comment again about the permissions.
> Greg

The binary is an 0405 a.out file. I'm told by Norman Wilson, who has
paper copies of the 2nd & 3rd Edition manuals, that 0405 binaries didn't
exist in 2nd & 3rd Edition.

I also believe that the files in the s2.tar tarball sent in by Dennis
are a whole year off, and so the date above should be Apr 14, 1972.
That dates the file just before the release of 2nd Edition.

I really need to sit down & outline my reasons for believing that the
dates are a year out. I'll do so soon & email it here!

Cheers all,
	Warren

Received: (from major at localhost)
	by minnie.cs.adfa.edu.au (8.9.3/8.9.3) id JAA41918
	for pups-liszt; Thu, 28 Oct 1999 09:49:29 +1000 (EST)
Received: from nose.cita.utoronto.ca (nose.cita.utoronto.ca [128.100.76.157])
	by minnie.cs.adfa.edu.au (8.9.3/8.9.3) with SMTP id JAA41914
	for <pups at minnie.cs.adfa.edu.au>; Thu, 28 Oct 1999 09:49:18 +1000 (EST)
From: norman@nose.cita.utoronto.ca
Message-Id: <199910272349.JAA41914 at minnie.cs.adfa.edu.au>
Subject: dc and date numerology
To: pups at minnie.cs.adfa.edu.au
Date: Wed, 27 Oct 1999 19:48:50 -0400
Sender: owner-pups at minnie.cs.adfa.edu.au
Precedence: bulk

Greg Lehey wondered about the date in

> There's a binary of dc from either 1st or 2nd Edition in the PUPS Archive:
>
> 	-r---wxrw- 0/0            6846 Apr 14 06:50 1973 bin/dc

1973 is indeed post-Second-Edition.  But it's not the right date; just as
the permission flags were different in the early years, so was the date
representation.  Here are some gleanings from old manuals that tell the
story.

The relatively recent ls or tar or whatnot that printed the line above
presumably interpreted the date as if it were in modern form: seconds since
1 Jan 1970 UTC.  So the raw number stored in the i-node was probably about
105000000 decimal (30 Apr 1973 in my time zone), or about 1200 days into the
epoch.

But the file system described in the First Edition manual takes the date
as a count of clock ticks since 1 Jan 1971.  The clock ticked at 60Hz,
so the date is really about 1200/60 = 20 days into the epoch; if this file
came from a 1e file system, it was written on 21 Jan 1971.

The trouble with keeping a 60Hz clock in a 32-bit number is that it takes just
a couple of years before it overflows.  A band-aid had been stuck on by the time
the Third Edition manual was printed: the base date changed to 1 Jan 1972.  So
maybe bin/dc was written on 21 Jan 1972 instead.  There's no way to tell just
from the bits in the i-node.

The modern time format (1-second resolution) appeared in the Fourth Edition manual.
It is probably not a coincidence that the file system format changed a lot at
the same time; groups appeared, permission modes changed to approximately their
current form, directory entries changed, and so on.

The 60Hz scheme seems to have come from the PDP-7, on which it made more sense;
the -7 has 36-bit words, so a 60Hz counter lasts 16 times longer.  I bet the
base date changed at least once between the original PDP-7 system and the PDP-11
as well, since 1 Jan 1971 seems too recent for the PDP-7 system.

See http://www.cita.utoronto.ca/~norman/old-unix/old-fs.html for many more such
grotty details, collected in an insomniac night with a stack of old manuals some
months ago.

Norman Wilson

Received: (from major at localhost)
	by minnie.cs.adfa.edu.au (8.9.3/8.9.3) id KAA42069
	for pups-liszt; Thu, 28 Oct 1999 10:02:33 +1000 (EST)
Received: from henry.cs.adfa.edu.au (henry.cs.adfa.edu.au [131.236.21.158])
	by minnie.cs.adfa.edu.au (8.9.3/8.9.3) with ESMTP id KAA42060
	for <pups at minnie.cs.adfa.edu.au>; Thu, 28 Oct 1999 10:02:26 +1000 (EST)
Received: (from wkt at localhost)
	by henry.cs.adfa.edu.au (8.9.2/8.9.3) id KAA26898
	for pups at minnie.cs.adfa.edu.au; Thu, 28 Oct 1999 10:02:25 +1000 (EST)
From: Warren Toomey <wkt@cs.adfa.edu.au>
Message-Id: <199910280002.KAA26898 at henry.cs.adfa.edu.au>
Subject: Re: dc and date numerology
In-Reply-To: <199910272349.JAA41914 at minnie.cs.adfa.edu.au> from "norman at nose.cita.utoronto.ca" at "Oct 27, 1999  7:48:50 pm"
To: 
Date: Thu, 28 Oct 1999 10:02:25 +1000 (EST)
Cc: pups at minnie.cs.adfa.edu.au
Reply-To: wkt at cs.adfa.edu.au
X-Mailer: ELM [version 2.4ME+ PL43 (25)]
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: owner-pups at minnie.cs.adfa.edu.au
Precedence: bulk

In article by norman at nose.cita.utoronto.ca:
> Greg Lehey wondered about the date in
> > 	-r---wxrw- 0/0            6846 Apr 14 06:50 1973 bin/dc
> 
> 1973 is indeed post-Second-Edition.  But it's not the right date; just as
> the permission flags were different in the early years, so was the date
> representation.  Here are some gleanings from old manuals that tell the
> story.

[ much omitted ]
 
Norman details the fact that early Unixes stored time in 60ths of a second,
i.e the normal clock tick, and as such, a 32-bit integer overflows in
around 2.5 years.

However, I think Norman is not exactly right when he said that the
tar archive was reinterpreting this 1/60 sec time in units of seconds.

Dennis Ritchie, with help from Keith Bostic and a DECtape drive, managed to
retrieve these files from an old DECtape. These old files were stored in
tap(1) archive format.

Dennis wrote a program to read in the tap(1) format archives and extract
their contents while trying to maintain the _correct_ permissions and
timestamps. Here is his email describing this:

	The tapes were written in either the 'tap' or 'tp' format, which
	are similar in that they have a directory of up to 192 entries at
	the start with names and other information including the size and
	tape address of the files.  'tp' was the later format, and was in
	use by November 1973, the date of the 4th edition manual.  With
	`tap', the times associated with the files were recorded in pre-modern
	units: sixtieths of a second, from an origin that changed.  The
	first three editions of the manual had BUGS sections noting that
	32 bits can represent only about 2.5 years in this unit, and this
	implied continuing crises as the time overflowed.

	I believe that the change to use seconds for Unix time took place
	along with the change to the C version of the operating system,
	which occurred about the end of the summer of 1973, and also that
	the change from `tap' to `tp' took place at the same time.  (This
	is consistent with the dates of the 3rd and 4th edition manuals).
	
	Thus the dates recorded with the `tp' tapes probably correspond
	reliably to the modification dates of the files at the time of
	saving them (of course, this gives only a upper bound on their
	creation, since they might have been copied or trivially touched
	just before saving them).
	
	Recovering the proper dates for the `tap' tapes is less reliable,
	because there was at least one change of epoch (from 1971 to 1972)
	during the period they could possibly have been produced.  I believe
	that the 1972 epoch is most likely the correct one for the tapes here.

In other words, Dennis had to guess the epoch when recovering these files.
He got it right with the `nsys' kernel files, because there is enough other
data lying around documenting the kernel rewrite from assembly to C, and
the inclusion of pipes into the kernel.

However, with the s2.tar archive, I think Dennis got the epoch one year out,
i.e everything should be dated a year earlier. The most obvious is that
there are so many 0405 magic a.out files in the archive, and apparently
this a.out format disappeared in the 2nd Edition.

Cheers all,
	Warren