[PLUG-TALK] PDP-8's and 10s Re: SpaceWar is back!

[Keith Lofstrom]

On Thu, Jun 06, 2024 at 08:23:11AM -0700, Galen Seitz wrote:
> A large team of tech nostalgia enthusiasts have made a PiDP-10, a
> replica of the PDP-10 mainframe computer first launched by the
> Digital Equipment Corporation in 1966
> 
> <https://www.theguardian.com/technology/article/2024/jun/06/reinventing-the-pdp-10>

I've never used a PDP-10, but did spend MANY evening hours
with a PDP-8 at Tektronix, as a 16 and 17 year old guest.
As I recall, one of the toggle switches on the '8 had a
short lever handle to enter a 12 bit word into magnetic
core memory.  That helped with toggle switch "touch
typing".  Your fingers read the switches while your eyes
read the octal off a programming sheet.

Typically, you enter the starting address and the first
word with the toggle switches, then toggle the lever to
enter one word of memory, then increment the address
counter with a toggle.  Then toggle in the next word. 

In PDP-8ish, you thought in octal "bytes", not
hexadecimal bytes.  The instruction set was small
enough to memorize.

A "short" twenty word program was enough to program the
PDP-8 to read a longer "bootstrap" program from the 
paper tape reader.  Sometimes a high speed tape reader
in the equipment rack, but usually the tape reader on 
the ASR-33 teletype "console".

That bootstrap program was complex enough to read a LONG
program from the paper tape reader (such as a two pass
FOCAL language compiler), or punch a program to paper tape,
or enable a DECTAPE magnetic tape reader on an expensive
$$$$$ *DELUXE" PDP-8 system. 

ASCII machines.  7 bit ASCII with 3 bit octal is weird.

Operating system?  With a maximum of 4K words of contiguous
memory?  That required a PDP-11, or an IBM 1130, both with
disk packs.  The IBM machines used EBCDIC coding rather
than ASCII.  Ugly hack.  IBM did have Fortran rather than
FOCAL.  I learned numerical methods using Fortran on the
1130, and kept some of the 2000-card source program decks
for those programs for a couple of decades. 

I never had access to a deluxe PDP-8.  Just as well; as an
obstreperous youth, I enjoyed searching for the equivalent
of "halt and catch fire" sequences on primitive computers.
Those machines were used for Tektronix daytime production;
mostly making programming tapes for production machine
numerical control systems. 

I was more than smart enough to get technical summer jobs,
but too unpredictable to leave unsupervised.  I haven't
improved much in the subsequent five decades.

 *
  *  Keith L.
***  

-- 
Keith Lofstrom          keithl at keithl.com