You know – or people without a smartphone knew – those everlasting, perennual, forever calendars. Today even those are computerized, see for example the months display here or the “everlasting calendar” here. For some hundreds of years they came printed on paper, and I had one in my little appointment calendar. They looked like this:
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| Click to enlarge. Source https://de.wikipedia.org/wiki/Datei:Immerw%C3%A4hrender_Kalender_S1.png |
Or continue here. The Schlüsselbuchstabe, key character g is the Tagesnummer, day number 5 there, so
a = 1,
b = 2,
c = 3,
d = 4,
e = 5,
f = 6 and
g = 0.
So I guess you can take the day number (0 to 6), add the numeric calender day, and try your luck in the Nendwich’s Tabelle III below.
Example. The year 1941 in table A is in the fifth column, go down to November of 1941 and you get an f, corresponding to 6. Add say the 30th of this November to 6, you get 36, a Sunday.
| Tabelle III | ||||||||
|---|---|---|---|---|---|---|---|---|
| 1 | 8 | 15 | 22 | 29 | 36 | 1 | Sonntag | |
| 2 | 9 | 16 | 23 | 30 | 37 | 2 | Montag | |
| 3 | 10 | 17 | 24 | 31 | 3 | Dienstag | ||
| 4 | 11 | 18 | 25 | 32 | 4 | Mittwoch | ||
| 5 | 12 | 19 | 26 | 33 | 5 | Donnerstag | ||
| 6 | 13 | 20 | 27 | 34 | 6 | Freitag | ||
| 7 | 14 | 21 | 28 | 35 | 0 | Samstag | ||
| Ergebniszahl | R7 | Wochenta | ||||||
That said, finally, here’s the story.
My friend Ulrich Bosler and I worked night shifts at the University of Berlin’s largest computer, an ICL 1904, back in 1968. We made an Exapt compiler, all in Fortran II, some 7000 punched cards. As students had to pass a little exam to be permitted to use this room full of computer and peripherals alone. But just as Adam and Eve were not permitted to eat apples from a certain tree, we were strictly forbidden to reload the executive, as the operating system was called. Normally it didn’t crash, but eventually it did. No blue screen at that time, no screen at all, they weren’t invented yet. The operating system was controlled by a teletypewriter in the middle of the room. When it stopped hacking along with its ten characters per second typing speed, we knew: sudden death had occured.
Should we have gone home, at two in the night, with four hours more computer time all for us? We didn’t want to. So we decided to “illegally” restart the computer.
This was done by reading in a bootstrap tape – not a magnetic tape, behold, but a paper tape roll as big as a frisbee (not invented yet). The system had a special optical reader for that, a luxury, and we carefully run the tape, and restarted the system all right.
Next thing was – just like later with the first PCs – that you had to enter time and date. I was nervous. After all, the next day everybody would see on the end of the log paper roll that we had tried to restarte the system, if we didn’t cover it with numerous lengthy log entries during the rest of the night. Finally the system asked me for the weekday. And then it didn’t accept that! Over and over again it insisted on a correct date. I typed it in all sorts of formats, with two digit year, with four digit year, with separating points or slahes or dashes, and got ever more nervous and confused.
My friend came to help me. He spotted the mistake right away: I had entered the wrong year, in my confusion. With the right year and the right weekday the ICL mainframe was satisfied and started to work.
Apparently the system had a perennual calendar built in to check the dates. This part of the startup program was later overlayed, a higher ranking assistant told me later in confidence.
But I thought of revenge!
Next time we had to reboot a crashed system, I took out my calendar – see above table A at Schaltjahre, leap years – and entered a year with the same day pattern long before the mainframe’s birth, like 1940 instead of 1968. Computers hadn’t even been invented then … The ICL 1904 didn’t know that, no Wikipedia there, and accepted the date. So we worked the final hours of our night shift back in the year 1940! Before leaving we corrected the date.
I had fooled the system. Triumph! Man wins technology. Computers are dumb, the human brain is unsurpassable. Artificial intelligence a misnomer, at that time not named yet though.
Final act. Destiny hits. Pride goes before destruction, a haughty spirit before a fall (ante ruinam exaltatur spiritus), Salomonic proverbs 16:18. Next time we were on at night, when I loaded our tapes – we had four of them, the compiled program, the input data with Exapt, machine tool output and one for overlays I think – the magnetic tape stations pulled in the tape, read the label, and instead of waiting patiently for the first read command, ate the label again and scratched it. After the second tape I realized that something was wrong, very wrong. My tapes were officially scrapped, made unreadable, were reformatted as you’d say today. Why? The tape’s “retention periods” of some five years were long gone since we had last written onto the tapes, back in fake 1940.
Magnetic tapes when wound up slowly, very slowly copy content from one tape round to the adjacent rounds. Correct reading is disturbed. With audio tapes you hear an echo, digital tapes just don’t read exactly any more. So tapes have to be re-written periodically, or at least rewound, to preserve their content. That’s why the retention period is checked.
For more about “our” ICL 1904 and the first story read Listening to Computer Bugs.
Another story: https://blogabissl.blogspot.com/2017/10/the-speaking-modem.html#modem
More stories: https://blogabissl.blogspot.com/2017/10/old-computer-stories-hp-2116-et-al.html
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Link directly to the story:
https://blogabissl.blogspot.com/2017/10/how-i-tried-to-trick-computer.html#retention
