[TUHS] Why do compress(1) and pack(1) use the .Z / .z extension?

Warner Losh imp at bsdimp.com
Sat Nov 28 05:00:25 AEST 2020

On Fri, Nov 27, 2020 at 10:17 AM Clem Cole <clemc at ccc.com> wrote:

> On Fri, Nov 27, 2020 at 8:08 AM Hans Wennborg <hans at hanshq.net> wrote:
>> I'm trying to find out why compress(1) uses .Z as filename extension.
>> My theory is that it was inspired by pack(1), which uses the .z extension.
> Yes.
>> However, I haven't been able to find any info on why pack(1) uses that
>> extension. Does anyone here know?
> No idea - but yes, Zucker used a .z at Rand when he wrote.
>> Some searching led me to [1] which is a man page for pack from AUSAM.
>> It's written by Steve Zucker in 1975, so perhaps the extension is z for
>> Zucker?
>> Was Zucker's pack(1) the first, though? This message [2] talks about a
>> Bell version.
> Zucker wrote it at Rand - early/mid 1970s. IIRC, It was later included in
> the original Harvard USENIX tape in the 'Rand' directory.  I believe that
> Rand Pipes (named pipes) are in the same directory. Although some of the
> Rand stuff was being shared by folks on the ArpaNet before USENIX existed
> and I think it made it to the wild before the first USENIX tape.
> It was really important back in the day.  Remember RK05's are only 2.5M
> bytes - source archiving and packing files was pretty important given the
> cost / byte of disk.
> I think there may have been an early version @ BTL - PWB may have
> distributed it also, but I'm fairly sure it was the Rand code that started
> it.  Noel might remember more than I.  I'm 90% sure we had it at CMU before
> we got either PWB 1.0 or UNIX/TS from Ted -- I want to say it we had it on
> 5th edition but maybe not.
> One of the PDP-10 folks will need to chime in here.  My memory is there
> was something like pack(1) on the CMU PDP-10s and 20s that I saw before I
> saw the UNIX tool [not sure why I think this, but it may have been SAIL
> program - I remember looking at a number of simple tools when I learn SAIL
> years and years ago - 74/75-ish].  IIRC they were not exactly the same
> format as the 10's were 36-bit words, stored 5 chars in a word, but it was
> the same idea.

Regardless of the early history, this is why gzip files end in .gz and not
.z. The pack'd files were considered too prevalent at the time to crowd
into that name space, even though this happened maybe 12 years after
compress started to displace pack.

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