Subject: Re: There is actually PDP8 users out there * STILL *

From: [email-masked] (Clyde Roby)
Date: 28 Feb 1994 16:24:14 GMT

Charles Lasner ([email-masked]) wrote:

[...stuff deleted...]

I don't consider myself a wizard for the LINC-8/PDP-8 line of computers
(even though when I was at WVU, we did develop a LINC-8 based OS, based
upon LAP-6 (using 8-character tags instead of number-letter tags).
This was in 1967 at the WVU Medical Center research labs...wow!

: Bonus question of the day:  Can anyone explain the reasoning behind the 
: LINC/LINC-8 instruction ZZZ (which was renamed QLZ in the PDP-12)?  (On a 
: scale of 1-10, this question is worth 8 frames of paper-tape leader/trailer.)

The Z register was used for the least significant 11 bits of a fractional
multiply (MUL) instruction, getting the Z register with the ZTA (Z to A)
instruction.  the ZZZ was the Z Zero Skip instruction (Bit 11 of Z=0).
I think that it was used for multiple precision arithmetic, e.g., floating
point packages, etc.

================================================================
Clyde G. Roby, Research Staff Member
Institute for Defense Analyses        Phone: (703) 845-6666
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From: [email-masked] (Charles Lasner)
Date: 2 Mar 1994 16:37:13 GMT

>This was in 1967 at the WVU Medical Center research labs...wow!

Not a wizard, but at least an old hat!  (And one whose name I know!  Any
of the WVU people still around?  I want to put some of the WVU stuff into
the sunsite archive.  One of the utilities is alleged to be a program to
stuff OS/8 files into an OS/8 file.)

>I think that it was used for multiple precision arithmetic, e.g., floating

I'll give you six of the 8 paper-tape frames.  You missed a key point
about the bit notation and the mnemonic itself, which is why it was changed.

Neglecting the LINC-8, which was on the fence as to whether to use
LINC-originated conventions or to use PDP-8 conventions, the ZZZ symbol
originates in the LINC, and was changed to QLZ on the PDP-12.  The reason
is that the low-order bit of the Z register is *NOT* bit[11], rather it's
bit[0].  Yes, the LINC registers are numbered in a non-pdp-8-like way of
right to left.  (I guess the LINC design comes from an ancient Hebrew
text :-).)  So, it's ZZZ because it's skip if the Z register bit Zero is
Zero.

On the PDP-12, there are no separate registers, so the Z register is
replaced with the PDP-8's MQ.  PDP-8 registers are always numbered left to
right (because the PDP-8 design comes from an ancient Hebrew text read in
a mirror :-)).  So they changed the symbol to QLZ.  (skip if "Q"  register
Low-order bit is Zero)

(On the LINC-8, most registers are PDP-8, so the -8-like notation dominates.)

cjl

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From: [email-masked] (Clyde Roby)
Date: 4 Mar 1994 17:49:35 GMT

: Not a wizard, but at least an old hat!  (And one whose name I know!  Any
: of the WVU people still around?  I want to put some of the WVU stuff into
: the sunsite archive.  One of the utilities is alleged to be a program to

: stuff OS/8 files into an OS/8 file.)

None of them are still at WVU as far as I know.  Last word
on some of them are -- Tom McIntyre lives in the Harvard, MA
area working for his son's company as a consultant (Tom used
to work for DEC at one time); Larry Pearson used to work at
DEC, too, but I think is a consultant, too; Darrell Duffy
used to work for DEC but is now in the Silicon Valley area
of California.  Jerry Farmer used to live in the Huntington
area of WV last time I heard (over a decade ago).

I don't think anyone would mind your putting the WVU stuff into
the sunsite archive.  Yea, the WVU gang used to do a lot of
little utilities for the PDP-12 and PDP-8 after we had worked
on the LINC-8 for awhile.

Maybe someone from WVU can respond -- anybody down at the
Computer Center, at the CS Department, or even at the Med
Center -- how about it?