Maand: november 2016

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.

Watching the birth of modern computing – EWD 35

EWD 35 starts out in typical Dijkstra way.

It is not unusual for a speaker to start a lecture with an introduction. As some in the audience might be totally not familiar with the issues that I wish to address and the terminology, which I will have to use, I will to give two examples as a means of introduction, the first one to describe the background of the problem and a second one, to give you an idea of the kind of logical problems, that we will encounter.

The story that EWD 35 tells is a brief history of the resolution to the scientific topic that brought Dijkstra his fame: the problem of synchronising parallel processes and the invention of the the concept of the semaphore for these types of problems in computing.

Today it is almost impossible to imagine a time in which this problem was still unsolved. Collaborating parallel processes, semaphores and indivisible operations have become a such a commodity in computing. But at that time computing meant sequential processes and parallelism of interacting processes was being looked at for the first time.

In 1959, the question was of whether the described capability for communication between two machines made it possible to couple two machines such, that the execution of the critical sections was mutually excluded in time. In 1962, a much wider group of issues was considered and the question was also changed to “What communication possibilities between machines are required, to play this kind of games as gracefully as possible?”

A side note. The word “required” and “possibilities” here do not cover the meaning of Dijkstra’s original in Dutch “welke communicatiemogeljkheden tussen machines zijn gewenst”. I would say “which communication facilities between machines are desired” – expressing better that Dijkstra is in the mode of designing the thing, thinking up these communication facilities.

Another side note, much of Dijkstra’s beautiful loose writing in Dutch is lost in this straightforward translation to English here. For example, we can translate “Jantje” to “Johnny” but in Dutch we have a completely different image in our head when we see Jantje than we someone, Dutch or non-Dutch, would have with Johnny.

Dijkstra uses the word machines in the paragraph quoted above. The terminology developed further and today we would call these, a bit more abstract, processes.

Further in his article he gives an insight into the potential for his “machines” and sees them simulated on a central computer. We really have to imagine this is a remarkable insight in the future. At that time computer ran single tasks. Running multiple processes at the same time on the same hardware was at best experimental. He makes this remark in the context of alternative ways of having machines collaborate and let them wait on each other by building in wait times in case they need access to the same resource.

However, if we consider now, that will be the majority of these machines will be simulated by a central computer so that any action in one machine can only be performed at the expense of the effective speed of the other machines, then it is very costly using a wait cycle to demand attention of the central computer for something completely useless.

The basic problem Dijkstra extensively examines is best described by Dijkstra in the following sentences. One machine wants to assign a value to a shared variable, after testing its value. For example something like:

if x=3 then x :=4 else x:=5

Another machine is trying to do the same thing, at the same time. What happens if machine 1 tests for the value of x, while at the same time machine 2 changes this value. Or, what happens if they both change the value of x at the same.

Dijkstra indicates a mechanism is necessary which he call indivisible actions. Today these things are indivisible, uninterruptible or atomic operations or instructions.

These two actions, assigning a new value and inquiring about the current value are considered indivisible actions, i.e. if both machines wish to “simultaneously” assign a value to a common variable then the value assigned at the end is one or the other value, but not some mixture. Similarly, if one machine asks for the value of a shared variable at the time that the other machine is assigning a new value to it, then the requesting machine will receive or the old or the new value, not a random value.

Having these instructions is key to the solution of the problem of interaction sequential processes.

In EWD35 Dijkstra then goes on to describe, in a rather lengthy paragraph – but remember this was front end research at that time – the invention of the semaphore in computing.

The programmed wait cycle that exists herein, is of course very nice, but it did little to what our goal. A tiny wait cycle is indeed the way to keep a machine busy “without effect” . However, if we consider now, that will be the majority of these machines will be simulated by a central computer so that any action in one machine can only be performed at the expense of the effective speed of the other machines, then it is very costly using a wait cycle to demand attention of the central computer for something completely useless. As long as the wait cycle cannot be exited, in our opinion the speed of this machine may be reduced to zero, To express this we introduce a statement instead of wait cycle, a basic instruction in the repertoire of the machines, that may take a very long time. We indicate this with a P (to Pass); in anticipation of future needs, we represent the statement “SX: = true” by “V(SX) – with V of “vrijgave” (in English: release) (This terminology is taken from the railway environment. In an earlier stage the common logical variables were called “Semaphores” and if their name starts with an S, it is a reminiscence of it). The text of the programs in this new notation is as follows:

“LXi: P(SX); TXi; V(SX); proces Xi; goto LXi” .

And you hold your breath, watching the birth of modern computing here in EWD 35.

The rest of the article provides the proof that this mechanism holds for any number of machines.

Dijkstra in EWD 32 on the tool, how it should be worthy our love, and show: Elegance and Beauty

In EWD 32 Dijkstra shares his “meditations” on the state of the Art (or rather Science, as he prefers to say) of Programming. Machine design was ugly, programming as a discipline was undeveloped. This was 1962.

Programmers were hired for applying tricks and Dijkstra loves the development that there is

… the slowly growing group of people who think it more valuable that the man should have a clear and systematic mind.

He goes on to discuss how programmer and machine designer should collaborate to create better machines and programming languages. Which was very necessary because Dijkstra believed at that time the computer manufacturing industry was taking over computer design from universities. But this brought a commercial angle to computer design that Dijkstra was unhappy with.

They seem to design for the customer that believes the salesman who tells him that machine so-and-so is just the machine he wants.

Dijkstra goes on to share his thoughts on how to improve The Tool – by which he means the programming language, translator and machine. Nowadays we have so many languages and machines, we hardly think about this tool. We think of tools as tools: a given rather than a thought. And of course we have massive debates about programming languages, hardware etcetera. But some of the concerns have disappeared. Nobody really seems to care anymore about machine design. It has become a commodity. It should be fast and robust. Hardware hardly provides any distinguishing features. If so, it is about size and energy, and no longer about performance and reliability.

But the last one he mentions is an eternal difference, one which we still haven’t landed on. And maybe we never will. Because it is a subjective one. A characteristic you wouldn’t expected in our Beta world of computers and programmers.

As my very last remark I should like to stress that the tool as a whole should have still another quality. It is a much more subtle one; whether we appreciate it or not depends much more on our personal taste and education and I shall not even try to define it. The tool should be charming, it should be elegant, it should be worthy of our love. This is no joke, I am terribly serious about this. In this respect the programmer does not differ from any other craftsman: unless he loves his tools it is highly improbable that he will ever create something of superior quality.

At the same time these considerations tell us the greatest virtues a program can show: Elegance and Beauty.

Araki en Maier in FOAM, 2015

2015. Amsterdam.

In the Stedelijk Museum large, dark paintings by Marlene Dumas. Not very colourful.

In FOAM lives Araki. With sensitive images of his life and especially his wife. The images demonstrate his love for her. After her death he shifts to pornographic and sadomasochistic topics. Then he finds rest in large, very colourful stills of flowers against a black background.

Vivian Maier has a small exhibition in the corridors and the small rooms in the back of FOAM. She  is at least as interesting. Wonderful street photography. Unfortunately it is extremely busy in the small passages of FOAM. Visitors shuffle breast to belly. I flee.

The Zeedijk is a mini Chinatown.

Edsger Dijkstra – blogger avant la lettre combines deep science with deadpan humor

Dijkstra, Holland’s most influential and remarkable computer scientist, was a blogger avant la lettre.
Her blogged in his EWDs (his initials – Edsger Willem Dijkstra) whatever he wanted to say – could be drafts of scientific papers or trip reports or angry letters.

His EWDs are fun to read. The language is precise but light, and pervaded with beautiful language, metaphors, humorous by-sentences and jokes.

If you can start a very theoretical discussion in this way, you are a genius of language, besides science. Here in EWD 28.

A machine defines (by its very structure) a language, viz. its input language: conversely, the semantic definition of a language specifies a machine that understands it. In other words: machine and language are two faces of one and the same coin. I am going to describe such a coin. I leave it entirely to you to decide which of these two aspects of the subject matter of my talk you think the most important as it is rather ridiculous in both aspects.

Who is going to write the biography of this broadly respected Dutch computer scientist?
Will probably end up kickstarting it myself.

Cees Nooteboom – 533 – een dagenboek

Een dagenboek.
Nooteboom verteld over zijn dagen in zijn Menorcaanse woning. Microscopische beschouwingen over zijn cactussen, de insecten rond zijn woning, de yucca, de ruines op Menorca.

Zorgvuldig beschreven in een nauwkeurige stijl die doet denken aan de veel minder bekende Tim Robinson die de Aran eilanden beschreef en ik leerde kennen via Boudewijn Buch.

Nooteboom schrijft over Brecht en Frisch. Over de muziek waar hij naar luistert.
En dan ook macroscopische beschouwingen over de reis van de Voyagers.
Over de kleine en grote dingen van het leven.

Een prachtige kruimel op de rok van Nooteboom’s universum. ( naar Lucebert)

Erich Maria Remarque – Im Westen nichts Neues

(All Quiet on the Western Front)
Incredible story about a German soldier on the Western front in France during the First World War.
Young men are mangled and deformed by the atrocities they experience in the trenches.
People die like flies. Soldiers must leave their wounded mates in the no man’s land between the fronts. From the trenches their hear them cry for help.
That same atmosphere as Celine’s Voyage au bout the la nuit.
Still, Remarque keeps some form of distance to the story, while describing the horrors of the war and the trenches. He analyses without becoming personal. Numb, dull, demoralised.

Unavoidable? The First World War – John Keegan

I recently visited Belgium, the area of Ieper. The remains of the First World War there are impressive.
I got interested and purchased The First World War by John Keegan,  which was according to the mass on google the essential guide to the First World War. My notes of this reading.
The incredible back story to this War. Starting with the long envisioned Schieffenplan, which had been cooking in Germany long before the war started. All the parties seems to be preparing their armies for a war. At a certain point the war became unavoidable.
How easily the war could have been prevented by some basic diplomatic actions.
Both sides hold on to very basic offensive tactic of frontal offence. Leading to many death. Both sides undertook these initiatives, which hundred thousand deaths or more in a week. This happened at all frontiers.
Besides the most well-known frontier in the West, mainly in Belgium and Norther France, the War was fought Africa in the German colonies, in the Middle East (Turkey being the ally of Germany in this war, in the Caucasus, Greece, Serbia, and at sea.
Germany was very successful with their submarines.
The war led or coincided with the downfall of the three large power centres in Europe: the tzar in Russia, the Austro-Hungarian emperor and the last emperor of Germany.
After the war Europe was fragmented in many new nation states due to the downfall of Germany and Austria-Hungary. This instabilities caused by this outcomes are still felt.
Keegan ends with the remark that is difficult to understand why a prosperous continent risked their achievements and values in ended up in such a bloody conflict.

A war that should never have happened. Not only was it meaningless. It was preventable.