Creating a Christmas card on a vintage IBM 1401 mainframe
righto.com
righto.com
It was quite a beast to maintain. The main part is a "train" of metal slugs with the letters, digits and a few symbols that hurtle around on a steel oiled track.
To print a letter H, the machine fires an electromagnet that drives a hammer onto the next H as it flies past.
One of the maintenance activities was adjusting the hammer strike, which you did by printing a page full of H's, and moving the strike forwards and backwards so that the left and right uprights of the "H" were both printed clearly.
The worst scenario with this machine was a "train crash", when one of the slugs dug into the train and all of the flying metal slugs smashed into each other in a giant screaming hail of destruction.
Other activities: - topping up the hydraulic fluid - replacing dead hammer drivers
My first modem is 28.8k, I guess you can call me young'un...
IBM used to use hydraulics pretty extensively. Their 2311 disk drives used hydraulic actuators to move the heads in and out over the platters. Hot pressurized oil and spinning magnetic media - a combination not made in heaven. I seem to remember stories about injuries caused by hydraulic oil piercing engineer body parts.
Thankfully they were phasing out as I started. Though living in the colonies, we used to see machines still working that were probably nowhere to be found in the US any more.
Hydraulic fluid injection injuries are appalling, and can often require amputation. I recall assisting a guy who had split a main line on a bobcat, and had oil spray into his hand. He lost most of his fingers.
I mean...I assume...backhoes and things need to have their fluid topped up, right?
From: hinojosa@hp-sdd.hp.com (Daniel Hinojosa)
Subject: Printer chain problems
Date: 6 Feb 89
A friend of mine told a story of one of these printers he and
another friend destroyed in a most interesting manner. These
printers had, it would seem, a sort of chain that held all of
the characters. I guess they held about three complete sets of
the alphabet plus special characters.
These chaps read the chain and created a file in their system
that had all of the characters of one pass in it. They gave the
command to print the file. Upon doing so the printer starts to
spin the chain, then SMACK! Trying to print all of those
characters at once while the chain was moving, didn't quite
work. The fellow said they found the print characters in
various parts of their office for years thereafter.
From: johnl@ima.ima.isc.com (John R. Levine)
Subject: Printing a line
Date: 8 Feb 89
...The letters on the print chain are all scrambled up. Each
time the chain moves, some fraction of the letters on the chain
will be in front of the place where those particular letters are
supposed to print, so the printer fires just those hammers.
Then the chain moves, some more hammers fire, etc.
The particular hack that Mr. Hinojosa and I described
reprogrammed the printer so it would think that every letter on
the line was correctly placed and so fire all the hammers at
once. That makes quite a lot of noise (normally, only 10 or so
of the 120 or 132 hammers go off at once) and moreover turned
out to use more power than the printer was prepared to supply
thus blowing the fuse and causing other problems.
From: darin@nova.laic.uucp (Darin Johnson)
Subject: Problematic printouts
Date: 9 Feb 89
Actually, the print chains are not in alphabetical order. They
are magically ordered by some arcane formula. Some of the
printers are designed so that the hammer will strike the
character just as the correct character is at the correct place
in the line (the chain rotates at very fast speeds). Often,
many characters will get printed at the same time, and no more
than 2 rotations of the chain are ever needed to print a line
(which is why they are fast). Presumably, the right set of
characters on a line will cause all the hammers (132) to strike
at the same time (while the chain is rotating).
I had related a story like this to a friend in college and
(unknown to me) had decided to try it. He spent a night
carefully going over the chain and determining the proper
sequence to send. The next evening, he decided to print his
file, and had me watch (only one line was printed). The job
printed and we ran downstairs. The printer was still rocking
slightly. Opening up the cover, the chain was still intact, but
had come completely off the drive that held it. We tore out the
offending sheet of paper with the incriminating line (smudged
and garbled) and complained to the operator on duty that the
printer was broken again. I don't think my friend ever tried it
again.If the chain spacing matched the print column spacing (what the stories describe), you'd fire a bunch of hammers at once, wait while the chain moves one position, fire a bunch more hammers, and so forth. This is much less efficient, since most of the time you're not doing anything. The 1401's approach also makes the circuitry simpler, since it only needs to check one character against one hammer at a time, rather than checking 132 characters at once.
The 1401's printer is actually even more tricky: the chain spacing and hammer spacing are almost in a 3:2 ratio, so each minuscule movement of the chain moves the alignment by 3 print positions and 2 chain positions. So you're never printing two chain positions consecutively. By the time the chain has moved enough for the alignment point to wrap around three times, the chain has moved one character's width and is ready to start again with the next character. 48 of these cycles gives each character one chance to be printed in each column, completing printing of one line. This all takes just 80 milliseconds.
The line printing mechanism is difficult to understand, so I made an animation to show what's happening: http://ibm-1401.info/KenShirriff-1403Animation.html
I would happily play on the punchcard machines for ages. When you turned one on (with the flip of a heavy switch) they'd start humming, giving a sense of coiled power. I loved the crisp thud of each punch, and the fluffy mass of little squares in the bin that collected waste. Compared with modern computing technology, they have a very industrial feel. I remember being delighted that my last name was all on the top row of the keyboard.
I also remember being absolutely fascinated by insert mode on the terminals. I could make shapes with the symbols and then make them move forward by arrowing back and holding down the spacebar. The slowly fading green glow of the phosphors was magical to me, as was the way each letter was composed of visible dots.
There was a haecceity, a thisness to early tech like this that I miss a little in comparison with the incredibly flexible devices of today. I wouldn't go back, of course, but I definitely get why people spent time maintaining and restoring relics like this.
If you have nostalgia for phosphor, but don't want a huge, hot, CRT in your office, and you have Mac, check out the terminal emulator "Cathode": http://www.secretgeometry.com/apps/cathode/
(No association. I just like the product.) It's extremely configurable, you can simulate a wide variety of tubes in various states of (dis)repair.
Probably the perfect way to play nethack.
I remember as a young child pounding on the keys to see how fast I could make it go, and later on, writing short stories just to hear the "thunk thunk thunk" (after all, I could've written them on the PC over on the desk, but the typewriter was a novelty).
This was in the 90s, and I recognize that you're probably talking about a couple of decades earlier. I think that the only cardpunch I've touched is the one next to the articles's 1401, at the Computer History Museum, in fact.
Not sure why/how they hired me for the summer to do systems hacking (lost in the mists of time), but I remember adding some feature or other to the WATFOR Fortran compiler. (Maybe some additional COMMON features?)
There was something ultimately satisfying about the fonts used and the way a finely-tuned 1403 would render characters (even lower case on special models!).