EDW 37 – a review of the new IBM 1620

In EWD 37 Dijkstra records a product review of the the new IBM 1620 computer, which came to the market in 1959.
As often, the article starts with a wonderful Dijkstra-esk introduction.

It is a good custom that scientific articles are reviewed and that no publisher ever thinks about starting a lawsuit or any other measures of vengeance against the author of a very unfavourable review of one of his publications.
I am not sure if it is the first review of a new computer ever, but it is an interesting one, and it goes quite deep into the technical aspects.
But not before making a justification for doing the review in general.
“It is a good custom that scientific articles are reviewed and that no publisher ever thinks about starting a lawsuit or any other measures of vengeance against the author of a very unfavourable review of one of his publications.

(BTW for the historians amongst us, the 1620 was considered the first “mini-computer”.)

With this in mind it is somewhat curious that it is not customary to review digital computers. Reviews of these scientific instruments are in some respects much more important: it is a pity if you have bought the wrong book, but it is much, much worse if you have bought the wrong computer.

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Foto from http://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP1620.html

It is my considered opinion, however, that this machine embodies some very fundamental mistakes and certainly after the publication of the two letters mentioned above I regard it as my duty not to remain silent any longer. Manufacturers should be warned for these mistakes in order not to be tempted to incorporate them in their future designs, also machine users should be warned for these mistakes in order to help them in not chosing the wrong machine and in order to create a climate where machines will be judged more by their fundamental properties.

Dijkstra surfaces two major flaws in the design of this computer.
An instruction for constructing subroutines (Branch And Transmit) that is basically unusable because it is impossible to use in nested subroutines.

Another problem Dijkstra identifies is with the design of the paper tape processing. And it wouldn’t be Dijkstra if he would not illustrate this shortcoming with a great metaphor.

But now a curious problem arises: the terminal Record XXX Mark which has been stored is indistinguishable from previous Record Marks which might have been read from the tape, and therefore the machine is faced with a problem that shows a striking resemblance to the prototype of an improper algorithm: a man asking the way and getting the answer “You go straight on and turn to the right just before the last steel bridge.”

Dijkstra goes on to criticise the implementation of the variable field addressing method. He proves the implementation in not only very uneconomic (wasting memory – “cores”), but also severely limiting memory management. So severe that he questions the intelligence of the designers of the computer.

I always wonder whether the designers of such machines have been aware of the restrictive consequences of the technique in question; if so, it is hard to respect their conscious decision to stick to it, if not, are they the people that should have been designing machines? I always wonder……

Looking at these shortcomings they seem quite hilarious, but these were the early days of computing.

Dijkstra concludes his review with a final scathing verdict. Not only the buyers must have been totally ignorant to have bought such a machine, also the manufacturer is to blame.

As the reader will understand, my recent study of the IBM 1620 has been a shocking experience: I knew that it was a rather small machine but I had never suspected that it would embody so many basic blunders. Personally, I cannot undergo such an experience without asking myself what its morals are.
One of the facts we have to face is that this machine, despite of its poor qualities, has been bought or rented. Either the customer is incompetent to judge what he is buying, or the contracts are signed by the wrong persons; in both cases the conclusion is that the fact, that other people have chosen a particular machine, is no guarantee whatsoever as far as its quality is concerned.

The next fact that we have to face is that this machine, despite of its poor qualities, has been produced, in this case even by a big firm with a long and considerable experience. The straightforward conclusion is, that nor the size nor the experience is a guarantee as far as the quality of the product is concerned. Well, we can think of various explanations for this apparent inconsistency, but the most obvious explanation predicts still more blunders in the more ambitious and more complicated products of the manufacturer in question.

Thank you very much. There you go, IBM.

Een gedachte over “EDW 37 – a review of the new IBM 1620

  1. The 1620 was put together under extraordinary constraints, namely: cost and a very narrow market view (scientific and educational). It was meant to be cheap: in today’s world that would mean cheap and nasty construction as well, but the 1620 was built like a tank. It was the instruction set that was underdeveloped simply because it had to be a cheap computer. In those days a small increase in instruction complexity could lead to a blow out in electrical circuitry. Yet IBM may well have listened to this criticism because the 1620 was not developed for long, and pretty soon the 360 took over the world.

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