I remember both the HP-21MX and PDP-11 lights as "glowing with varying brightness" but you could still figure out what your code was doing by just *how* bright individual bits were . . . I'm going to have to make a USB blinky-lights console for my Mac . . . maybe I'll put some toggle switches on it too. On Sun, Apr 8, 2018 at 9:20 PM, Bill Gosper <billgosper@gmail.com> wrote:
I've mentioned here before the amazing console lights of the Univac 1206 (https://en.wikipedia.org/wiki/AN/USQ-20): "The machine was the size and shape of an old-fashioned double-door refrigerator <https://en.wikipedia.org/wiki/Refrigerator>, about six feet tall (roughly 1.80 meters)." Unmentioned: Those doors were inches thick and closed like a bank vault with interlocking brass teeth. The photo shows it up on a palette to admit the prodigious quantity of air that it sucked and exhausted out the stack on top. It could Bernoulli-levitate a football.
The console lights were neon-like, and were actually push buttons that complemented the bit they indicated, which seemed to include every bit in the processor. E.g., you could compute the first few factorials with a zero-instruction program by putting the processor into the state: Single step, Repeat Advance, Multiply Immediate 1.
I remember the amazement of the undergads that the PDP-1 lights didn't blink. The machine was so fast that they just glowed with varying brightness.
Except for one. The early models had a light labeled Halt Store, which no one had ever seen lit, until someone left a paper tape on the console labeled "Turn on Halt Store".
(The IBM blinking reflected slow IO devices.)
The PDP-1, like the Univac 1218, was 18bit 1's complement, as favored by Seymour Cray. The objection to 1's complement was that x+(-x) gave 11111... = -0. The PDP-1 simply "gronked" -0 via a special kudge (which missed a single example). Cray ingeniously avoided the -0 problem via hardware subtract with end-around borrow instead of hardware add with end-around carry.
The story at Univac was that Cray refused to cooperate with the 1206 design team or even accept the specifications of management. When the deadline came, the design team had nothing, and management was forced to build Cray's solo design. --rwg
Date: 2018-04-08 09:17 From: Victor Miller <victorsmiller@gmail.com> To: math-fun <math-fun@mailman.xmission.com> Reply-To: math-fun <math-fun@mailman.xmission.com>
In the summer of 1966 I was working at the Rome (NY) Air Development Center, on a Univac 1218 computer (a militarized verson of the 418). It was an 18 bit ones-complement machine. On the console were two banks of lights each in a 6 x 3 format. The machine had a primitive time sharing system, and the lights on the console normally displayed a pattern which was I L (for idle loop). I found out where the pattern was stored and one day I changed it to read FU. The Univac engineer came in, saw it, and said "things aren't that bad, arey they?". I just stared at him, and he said, well, I guess they are. _______________________________________________ math-fun mailing list math-fun@mailman.xmission.com https://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun
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