"Computing girls"

The Computing Girls were also known as Van Wijngaarden's girls, as it was Van Wijngaarden who introduced these women to mathematics.

Eddy Alleda, Dineke Botterweg, Ria Debets, Marijke de Jong, Bertha Haanappel, Emmy Hagenaar, Truus Hurts, Loes Kaarsenmaker, Corrie Langereis, Reina Mulder, Diny Postema and Trees Scheffer formed a group called the Computing Girls. As each of them had completed high school with exceptionally high grades in mathematics, they were considered computing wonders. Bertha had a 9 (on a scale from 0 to 10) for maths on her final grade list. It was her maths teacher who knew some people at the Mathematical Center and suggested she could become a 'computing girl'. She had no idea what the profession contained, but as she was flattered by being asked for such a job, she took it.

Eddy Alleda came to the Mathematical Center as a side job to pay for her math education at university, but she was so enthusiastic about the work that she put her studies on hold and started working at the Mathematical Center full time.

Van Wijngaarden

The girls received a complete mathematical education at the Mathematical Center by Van Wijngaarden. When the diploma "Mathematical Computing" was introduced, near the end of the fifties, the computing girls had already stopped working. Nevertheless Van Wijngaarden promised that they would receive their diploma after all, as Van Wijngaarden felt that they had earned this distinction simply for their experience in the field. Unfortunately he did not get his way, because the girls had already quit.

Van Wijngaarden was very proud of his computing girls, so he made sure they were taken great care of in every way. Their education was one of the ways he showed his appreciation. Another was their salary, which amounted 150 up to 200 Dutch guilders, roughly twice the wage of a secretary. Truus's brother almost collapsed mentally after he heard what she earned; six years older her senior he didn't even earn half the wage of his little sister.

The Computing Girls and Bram Loopstra

Left to right in the back (standing): Marijke de Jong, Dineke Botterweg, Eddy Alleda, Diny Postema and Emmy Hagenaar. Left to right sitting down: Ria Debets, Truus Hurts and Bram Loopstra (MC employee, naturally not a computing girl)

Complicated Work

The work done in the early years of the Mathematical Center consisted mostly of long drawn calculations that are now considered standard computer calculations. A good order took months to complete. They differentiated, integrated and iterated, number by number they computed whole table books. The blue book 'Interpolation and allied tables' was indispensable, as was the preparatory work of Van Wijngaarden and his assistants with whom the work started. They could manipulate complicated integrations to something much easier to calculate, but at the same time using every letter of the alphabet in the reduced calculation. Some clients also wanted their results returned to them graphically. Sometimes they also just made drawings for themselves, so the results could be guessed faster and some calculations to get a more accurate result could be made.

Van Wijngaarden and his assistants had means of checking results fast as well, so making an error wasn't very problematic. Only with calculations difficult to check two people had to independently compute the results. Another common trick was to divide big assignments into several smaller blocks that could be easily overseen and checked. The assignments came in forms from lists of numbers with rules and instructions to long drawn formulas. Being excellent mathematicians they could do it worthy of Van Wijngaardens pride. The computing work was very lively; during the work the girls would sing, laugh, chat and gossip.


For working with the big computing machines they needed to learn how to program. A crash course from Edsger Dijkstra taught them the very subject as well as calculating in binary. The girls ended up being deft programmers, preparing the work, making the punch cards and finally importing the program in the machine.

With everything they were taught they got a solid computer science education, even before anybody considered it a subject. When foreign guests visited the Mathematical Center Van Wijngaarden always took them to the computing department to show what the computing girls did. He liked to pride himself of the fact that no other computing department in the country was of similar quality and could perform similar high standing feats as the Mathematical Center.


Van Wijngaarden showed his attachment to his girls when Truus had announced she wanted to quit the job to brush up her English skills by following classes. He refused her to do so. Instead he organized an exchange for her and Dineke with the National Physical Laboratory in Teddington, Middlesex, UK. Because of this exchange Truus would keep working at the Mathematical Center while also training her English at the same time. The time at Teddington was mainly spent on learning matrix inversions, interluded with trips to London every now and then.

It wasn't only Van Wijngaarden who appreciated the computing girls. Far from being mere “infantry”, they were adressed in the organisation on their intellect. They were also very dedicated to their job.

Coffee Mills

When they started using machines at the Mathematical Center calculating was still a lot of manual labor. The computing girls were the ones that did it, using mechanical desk calculators, or coffee mills as they jokingly called them. They were very slow, but there were many ways to speed it up. Multiplying was just a wind on the handle, but multiplying by nine could be done much quicker. Just move the decimal point by one place, turn the machine in the other direction once, and that was all.

They also worked on big table calculators and from 1954 they used the first Dutch computer to do their calculations, although they did other things as well. Truus for example had been soldering on the ARRA II for a week, as it had to be finished. Working with the ARRA II was fun to them, not at all a threat, and unemployment didn't exist yet. One time Eddy had to do a job with fifty decimals, and she was very glad to be able to do that on the ARRA II. It simply saved her processing the numbers on 4 different manual machines. The ARRA II made it possible to do it all at once. They found the Amsterdam computer dumb, as it couldn't take over any calculation, and it was just another tool where every step of the calculation had to be pre-chewed step by step so it would behave as it was told. It couldn't work on its own, and somebody had to stay with it at any time to handle the errors the machine produced.

The Computing Girls in 1986

Some of the Computing Girls at a reunion in 1986. From left to right: Truus Hurts, Dineke Botterweg, Bertha Haanappel, Eddy Alleda


The computing girls find the present day computer situation inferior to the pioneering work. It has become too easy and they believe they understand how the computers worked a lot better than the young people working on them nowadays do[1]. They did everything in machine language and had to take account of the fact the machine had only a limited amount of memory for example, making sure you didn't get overflow. If you knew overflow would occur, some of the lower digits had to be dropped to prevent it. If not enough intermediate solutions fit in the memory then punch tape was available as external memory: they simply wrote to the punch tape, and by taping it to the end of the incoming tape it could be read again.


It wasn't all work and no play during the period the girls worked at the Mathematical Center. It was an important time to them in many other ways. The girls shared a lot of activities, from vacations to parties. Coming in as seventeen year old "bobby soxers," they raised each other, as they described themselves, and left the center as women. They did work that nobody on the outside really understood.

"Ah! Yes, a Mathematical Center also functions like a sort of marriage agency of course."

Bertha, one of the Computing Girls.

As they chatted, gossiped and sang during their work, they were by far the most cheerful group in the whole Mathematical Center, between all the technicians. Bertha said that "mathematicians in the computer sector are usually so fanatic that they are thirty before they realize that mankind consists of two different genders." Much of that time has stuck with them, and they are inimitable in mental arithmetic. Truus: "I still enjoy it in the supermarket to have the exact amount of money in my hand while they are still ringing up the products. We can't be surpassed in that."


After their time at the Mathematical Center they didn't use their knowledge in Computer Science anymore. They got married, had children, and devoted themselves to their family, much like the normal pattern in those days. They do believe though that if they had stayed working at the Mathematical Center they would have eventually closed the gap with the scientific workers.

Eddy Alleda was the only exception. She didn't consider herself suitable for household work, and worked as a math teacher later on. While preparing the food in the kitchen she had her programming handbook lay open next to the stove on the fridge.

Of course, even until today, the computing girls are still proud that they have been part of the group that built the first Dutch computer.


Previous Image 1/2 NextComputing Girls and LoopstraComputing Girls and LoopstraThe Computing Girls together with Bram Loopstra. Standing up in the back, left to right: Marijke de Jong, Dineke Botterweg, Eddy Alleda, Diny Postema and Emmy Hagenaar. Seated: Ria Debets, Truus Hurts and Bram Loopstra.