[TUHS] PDP-11, Unix, octal?

[TUHS] PDP-11, Unix, octal?

[Noel Chiappa]

    > From: Warren Toomey

    > Something I've been meaning to ask for a while: why Unix and octal on
    > the PDP-11? Because of the DEC documentation?

Yeah, DEC did it all in octal.

    > I understand why other DEC architectures (e.g. PDP-7) were octal: 18b
    > is a multiple of 3. But PDP-11 is 16b, multiple of 4.

Look at PDP-11 machine code. Two-op instructions look like this (bit-wise):

  oooossssssdddddd

where 'ssssss' and 'dddddd' (source and destination) have the same format:

  mmmrrr

where 'mmm' is the mode (things like R, @Rn, etc) and 'rrr' is the register
number. All on octal boundaries. So if you see '010011' in a dump (or when
looking at memory through the front console switches :-), you know
immediately that means:

  MOV	R0, @R1

Much harder in hex... :-)

	Noel

[TUHS] Article on 'not meant to understand this'

[Steve Johnson]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 1595 bytes --]

I was well aware of the comment in V6, but had no idea what it
referred to.   When Dennis and I were porting what became V7 to the
Interdata 8/32, we spent about 10 frustrating days dealing with savu
and retu.  Dennis did his most productive work between 10pm and 4am,
while I kept more normal hours.  We would pore over the crash dumps
(in hex, then a new thing for us--PDP-ll was all octal, all the
time).  I'd tinker with the compiler, he'd tinker with the code and
we would get it to limp, flap its wings, and then crash.  The problem
was that the Interdata had many more registers than the PDP-11, so the
compiler only saved the register variables across a call, where the
PDP-11 saved all the registers.  This was just fine inside a process,
but between processes it was deadly.  After we had tried everything
we could think of, Dennis concluded that the fundamental architecture
was broken.  In a couple of days, he came up with the scheme that
ended up in V7.

It was only several years later when I saw a T-shirt with savu and
retu on it along with the famous comment that I realized what it had
referred to, and enjoyed the irony that we hadn't understood it
either...

Steve

----- Original Message -----
From: "Brantley Coile" <brantleycoile@me.com>
To:"Larry McVoy" <lm at mcvoy.com>
Cc:<tuhs at tuhs.org>
Sent:Mon, 16 Jan 2017 05:11:02 -0500
Subject:Re: [TUHS] Article on 'not meant to understand this'


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://minnie.tuhs.org/pipermail/tuhs/attachments/20170116/a2320686/attachment.html>

[TUHS] PDP-11, Unix, octal?

[Warren Toomey]

On Mon, Jan 16, 2017 at 11:10:37AM -0800, Steve Johnson wrote:
>    We would pore over the crash dumps (in hex, then a
>    new thing for us -- PDP-11 was all octal, all the time).

Something I've been meaning to ask for a while: why Unix and octal on the
PDP-11? Because of the DEC documentation?

I understand why other DEC architectures (e.g. PDP-7) were octal: 18b is
a multiple of 3. But PDP-11 is 16b, multiple of 4.

After all, Unix had its own assembler, so was there a need/reason to
use octal?

Cheers, Warren

[TUHS] PDP-11, Unix, octal?

[Lars Brinkhoff]

Warren Toomey wrote:
> I understand why other DEC architectures (e.g. PDP-7) were octal: 18b
> is a multiple of 3. But PDP-11 is 16b, multiple of 4.  After all, Unix
> had its own assembler, so was there a need/reason to use octal?

Octal is a natural fit for the instruction set encoding.

[TUHS] PDP-11, Unix, octal?

[ron minnich]

octal was also a good fit for a lot of the other dec systems of the time,
notably the 8 and the 10. I actually found octal to be a pain in the neck
on the -11: values and addresses were 377, or 177777 and 377777 and ...
bleah. I was glad when hex came along.



On Mon, Jan 16, 2017 at 1:04 PM Lars Brinkhoff <lars at nocrew.org> wrote:

> Warren Toomey wrote:
> > I understand why other DEC architectures (e.g. PDP-7) were octal: 18b
> > is a multiple of 3. But PDP-11 is 16b, multiple of 4.  After all, Unix
> > had its own assembler, so was there a need/reason to use octal?
>
> Octal is a natural fit for the instruction set encoding.
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://minnie.tuhs.org/pipermail/tuhs/attachments/20170116/810028c8/attachment.html>

[TUHS] PDP-11, Unix, octal?

[Erik E. Fair]

When I learned DG NOVA assembler in the mid-1970s, octal was it - it was everywhere. I didn't see hexadecimal notation until 8-bit microcomputers started using it in the late 1970s and early 1980s.

Just a change in culture, I'd suppose. Hex fits neatly into a byte, and we don't seem to see computers with word sizes that aren't a multiple of 8 any more.

	Erik <fair at netbsd.org>

[TUHS] PDP-11, Unix, octal?

[Steve Johnson]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 571 bytes --]

The mainframes of the 60's and 70's all used 6-bit characters (and
often different encodings for the non alphanumeric characters).  So
the Unix folks, including me, had experience with octal long before
Dec.

Steve

----- Original Message -----
From: "Warren Toomey" <wkt@tuhs.org>

 Something I've been meaning to ask for a while: why Unix and octal on
the
 PDP-11? Because of the DEC documentation?


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://minnie.tuhs.org/pipermail/tuhs/attachments/20170116/7a23ba1d/attachment.html>

[TUHS] PDP-11, Unix, octal?

[William Pechter]

And DEC used octal from the 1959 PDP1 through the VAX  which was 
announced on October 1977.

The PDP11 register front panel was painted to make front panel octal 
programming easier -  breaking out the three bit patterns.
Octal was deep in the DEC history and front panel flipping fingers.
I'll never forget 014747 (single instruction memory decrement test (move 
the pc to address pc - 2...


Bill


Steve Johnson wrote:
> The mainframes of the 60's and 70's all used 6-bit characters (and 
> often different encodings for the non alphanumeric characters). So the 
> Unix folks, including me, had experience with octal long before Dec.
>
> Steve
>
>
>
>     ----- Original Message -----
>     From:
>     "Warren Toomey" <wkt at tuhs.org>
>
>
>     Something I've been meaning to ask for a while: why Unix and octal
>     on the
>     PDP-11? Because of the DEC documentation?
>
>


-- 
Digital had it then.  Don't you wish you could buy it now!
pechter-at-gmail.com  http://xkcd.com/705/

[TUHS] PDP-11, Unix, octal?

[Joerg Schilling]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 635 bytes --]

"Steve Johnson" <scj at yaccman.com> wrote:

> The mainframes of the 60's and 70's all used 6-bit characters (and
> often different encodings for the non alphanumeric characters).  So
> the Unix folks, including me, had experience with octal long before
> Dec.

Bit IIRC, this has been done with 10 6 bit chars in a 60 bit word.

Did people use octal in this area?

Jörg

-- 
 EMail:joerg at schily.net                  (home) Jörg Schilling D-13353 Berlin
       joerg.schilling at fokus.fraunhofer.de (work) Blog: http://schily.blogspot.com/
 URL:  http://cdrecord.org/private/ http://sourceforge.net/projects/schilytools/files/

[TUHS] PDP-11, Unix, octal?

[Nelson H. F. Beebe]

Joerg Schilling asks today:

>> this has been done with 10 6 bit chars in a 60 bit word.
>> Did people use octal in this area?

I worked on a CDC 6400 with both NOS and KRONOS operating systems in
the 1970s.  The 6400/6600/7600 family were definitely in the octal
world.  Initially, the character set was 6-bit, with one character
reserved as an escape to mean that the next 6-bit chunk was to be
included, giving a 12-bit representation that added support for
lowercase letters (a feature that we could only get on our IBM 360 and
Amdahl 470 mainframes with a once-a-night change of the line printer
glyph chain).

Here is a quote by the lead architect, James E. Thornton, who wrote
the 1970 book, ``Design of a Computer: the Control Data 6600'', and
the 1980 history paper ``The CDC 6600 Project''
(http://dx.doi.org/10.1109/MAHC.1980.10044):

>> The selection of 60-bit word length came after a lengthy
>> investigation into the possibility of 64 bits.  Without going
>> into it in depth, our octal background got the upper hand.

That comes from page 347 of the paper.

-------------------------------------------------------------------------------
- Nelson H. F. Beebe                    Tel: +1 801 581 5254                  -
- University of Utah                    FAX: +1 801 581 4148                  -
- Department of Mathematics, 110 LCB    Internet e-mail: beebe at math.utah.edu  -
- 155 S 1400 E RM 233                       beebe at acm.org  beebe at computer.org -
- Salt Lake City, UT 84112-0090, USA    URL: http://www.math.utah.edu/~beebe/ -
-------------------------------------------------------------------------------

[TUHS] PDP-11, Unix, octal?

[William Cheswick]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 1025 bytes --]


> On 17Jan 2017, at 10:14 AM, Nelson H. F. Beebe <beebe at math.utah.edu> wrote:
> 
> the 1970s.  The 6400/6600/7600 family were definitely in the octal
> world.  Initially, the character set was 6-bit, with one character
> reserved as an escape to mean that the next 6-bit chunk was to be
> included, giving a 12-bit representation that added support for
> lowercase letters 

We called it “half-ASCII”, escaping with codes 74B and 76B.  As far as I recall, it only worked
on some versions of some of the timesharing systems in some modes.  We never had a lower
case print chain at Lehigh, SO ALL OUR OUTPUT WAS IN UPPER CASE.

And don’t get me started on 63- vs 64- character set.

The availability of ASCII on other operating systems was a great improvement in my life.
And certain neurons still remember crap like 22B is R in display code.

ches

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://minnie.tuhs.org/pipermail/tuhs/attachments/20170117/0a2e9aa8/attachment.html>

[TUHS] PDP-11, Unix, octal?

[Joerg Schilling]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 902 bytes --]

Warren Toomey <wkt at tuhs.org> wrote:

> On Mon, Jan 16, 2017 at 11:10:37AM -0800, Steve Johnson wrote:
> >    We would pore over the crash dumps (in hex, then a
> >    new thing for us -- PDP-11 was all octal, all the time).
>
> Something I've been meaning to ask for a while: why Unix and octal on the
> PDP-11? Because of the DEC documentation?
>
> I understand why other DEC architectures (e.g. PDP-7) were octal: 18b is
> a multiple of 3. But PDP-11 is 16b, multiple of 4.
>
> After all, Unix had its own assembler, so was there a need/reason to
> use octal?

Note that the people wo did this, used the 18 bit machines before.

Jörg

-- 
 EMail:joerg at schily.net                  (home) Jörg Schilling D-13353 Berlin
       joerg.schilling at fokus.fraunhofer.de (work) Blog: http://schily.blogspot.com/
 URL:  http://cdrecord.org/private/ http://sourceforge.net/projects/schilytools/files/

[TUHS] PDP-11, Unix, octal?

[ron minnich]

On Tue, Jan 17, 2017 at 6:12 AM Joerg Schilling <schily at schily.net> wrote:

>
>
> Note that the people wo did this, used the 18 bit machines before.
>
>
>
As steve johnson pointed out, just about everything around then was octal.
I think IBM brought widespread use of hex with the 360 ca. 1964, but to
most other vendors octal was a way of thinking as your interesting quote
points out.

As for character formats, on e.g. the pdp-10 you had lots of choice,
including 6 6-bit chars or 7 5-bit chars with one bit left over as common
... I also recall people used to complain about the inefficiencies inherent
in 8-bit character formats ...

I for one was still pretty glad to see octal mostly go away.

ron
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://minnie.tuhs.org/pipermail/tuhs/attachments/20170117/25958d31/attachment.html>