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Ken Ross & Paul Laughton

What was it like to use a computer without an operating system? We seldom ask ourselves this question, used as we are to download and install the operating system most adapted to our hardware at hand. But merely 60 years ago, the IBM 1401 was the most widely used computer system in the planet, and it did so without a matching operating system. How did it work?

Enter Paul Laughton and Ken Ross from the Computer History Museum. We have already published articles about computer history museums in this magazine, so it should be no surprise to the reader that we are very keen to share this kind of content. This month’s Vidéothèque movie is a demo of the IBM 1401 on YouTube.

Ken and Paul are industry veterans; the former is an MIT alumni, while the latter studied programming at Virginia Tech in 1965, and later “happily” worked as a programmer at Apple, IBM, Logitech, and Atari.

To give an idea of the importance of the IBM 1401, suffice to say that it is considered the “Ford Model T” of the computer world; the first widely available, mass-produced, affordable computer system in history (affordable to businesses, that is.) Its impact was such that, by 1965, when its successor, the IBM System/360, was introduced, 50% of all computers in the world were IBM 1401s. Fifty percent; think about that for a minute.

(Of course, there were far fewer computers back then; while Neil Armstrong was walking on the moon, more or less at the time when my mother became an IBMer in Buenos Aires, Argentina, there were circa 15’000 IBM 1401 deployed worldwide. The Intel 4004 was just a few years away.)

Each one of these machines brought IBM a hefty 2’500 USD/month in 1969 money. Let us do some quick math without considering depreciation or discounts: 15’000 machines bringing 2’500 USD/month in 1969… that is about half a billion a year (in 1969 dollars) or about 3.7 billion dollars in 2023 money. That is enough cash to finance the creation of, say, a research center in Boca Raton, Florida, where the IBM 5150 could be invented one day. Or to pay for all the lawyers required to handle the DoJ vs. IBM trial from 1969 to 1982. Pick whichever suits you best (pun intended.)

The IBM 1401 was widely praised in its time, externally for its reliability and durability, and internally for being a goddamn cash cow. What did people do with them? IBM 1401s were routinely used for sales analysis, inventory, and payroll; they spent most of their time just tabulating basic info in and out. It is one of the few computers in history that cannot run Doom. The IBM 1401 was also a notable huge energy black hole, eating up to 12’000 watts of energy, not counting the air conditioning required to absorb all the heat produced by these beasts.

The system shown during the demo consists of the IBM 1401 CPU (using binary-coded decimal variable-length words, handling only uppercase characters), together with an IBM 1403 printer (“the most advanced of its time” according to Ken, but also the noisiest), an IBM 026 printing card punch (mostly operated by women back in those days, a job that probably my mother had at some point), a card reader, a sorter, and a few IBM 729 tape drives in the background.

The machines were as mechanic as they were electronic, as revealed by the smell of oil in the room, and by the racks of cabled programs on boards, used to read 80-column cards and do something with their data. Program libraries, decades before the npm registry, consisted of racks full of boards. And RAM modules were “core memory” blocks, consisting of iron donuts, where a character (not yet called “byte”) cost 5 dollars, or 50 dollars of 2023. That would be 7000 dollars per tweet, thankyousomuch.

The video shows two demos: the first one is the sorter, feeding 1000 cards a minute and placing them in order according to a column number. Need to sort according to a second column? Move the knob, place the cards again on the feeder, and wait a few seconds. In short, a hardware machine literally wired to perform something similar to what an algorithm like quicksort can do in software. These machines were the same ones used to sort social security data with the information of millions of US citizens.

The second demo is of the IBM 026 keypunch machine, where one of the attendees gets to write her name on a card, make a copy of it, and be offered a job for 0.80 cents/hour, which is like 8 dollars per hour in 2023, roughly 1280 USD/month in today’s money. (For punching cards. Salaries were definitely higher back then.)

The card punched by the museum guest was fed as data into a “big print” program, generating a single page of print output on the IBM 1403 printer. Simple but effective, and surprisingly fast.

As Paul says at 17:49: “There’s no operating system on this machine.” The program contained in the stack of punched cards must include the required instructions for the CPU to read the rest of the program; that is why the first card is called the “bootstrap card” and contains instructions to do that. Just like in today’s computers, where the first thing a CPU does when powered up is to read the boot record of a disk to find the rest of the operating system to load.

Ken and Paul also discuss the subject of magnetic tape. To give an idea of their capacity, a reel of tape could carry the same information as 200’000 cards. Knowing that a single box contained only about 2’000 cards, one can see Moore’s law at work during the past 60 years. The tapes were made of Mylar, essentially the same substance used on VCR tapes, but to avoid stretching it, the IBM 729 would use vacuum tubes to suck it out of the reels and buffer it, to reduce the strain on the tape and increase its longevity. A very curious and original method.

At the end of the operation, Paul demonstrates how to perform a “high-speed rewind” and also how to use the “write ring” to make tape reels read-only and prevent their accidental erasure. IBM recommended storing information in two reels, as a timelessly wise backup strategy: one reel should be stored on-site, the other off-site.

Complement this month’s Vidéothèque movie with a recording of the announcement of the IBM 1401 in 1960, the Computer History Museum website page about the IBM 1401, and with a 1970’s IBM vintage promotional film to continue your trip across the past, the latter announcing the burgeoning era of operating systems at 19:40: “enabling the simultaneous processing of many jobs.”

Or just listen to the late Jóhann Jóhannsson‘s 2006 opus “IBM 1401 A User’s Manual”, available on Spotify, on YouTube, or on Apple Music. You can thank us later.

Cover snapshot by the author.

Continue reading Abraham Silberschatz, Peter Baer Galvin, & Greg Gagne or go back to Issue 056: Operating Systems. Did you like this article? Consider subscribing to our newsletter or contributing to the sustainability of this magazine. Thanks!
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