From Axel’s archives: a pocket calculator eating magnetic stripes

After I blogged about how I used a logarithm book in school to “compute” something like log(99) I want to write a little bit about the “computer” I worked with while being at the university studying electrical engineering.

This was the time between 1980 and 1983. As you all know Personal Computers had just been invented at that time. The IBM PC  was announced in August 1981, thus those computers just became available while I was a student but you can imagine that at the beginning they were not used widely and they of course have been too expensive for a poor student.

During my training at IBM I learned how to write Assembler programs on a System/370 and how to write APL programs on an IBM 5100 Portable Computer. Nevertheless, those computer have not been available for me as a “personal” computer during my time at the university.

The “computer” I started using at the university was what has been called a programmable calculator: the TI-59. If I remember correctly I had to pay more than 500 Deutsche Mark for this, which is around 250 € nowadays or around 330 $. Programming was done with a very low level language: statements consisted of three letter words either describing one of the keys of the calculator or some constructs like a label (LBL) or a goto (GTO) or STO and RCL to store and recall a number from a register. Number of register and program steps could be configured depending on how I wanted to use the memory, the largest program I could write could consist of 512 steps.

Programs could be stored on or read from a magnetic stripe through a magnetic card writer/reader built into the upper part of the calculator below the red LCD display. A video in this Wikipedia article illustrates nicely how this worked.

The most complex program we wrote was for dimensioning an electronic transistor circuit requiring some iterative algorithm to correctly determine the voltage at the different pins of a transistor. Besides this we of course also spent some time on writing first computer games, like the Lunar Lander ( text only version ), where the player has to enter the right amount of fuel to be used at the right time for slowing down the vehicle as it is coming down to achieve a safe landing, while the “computer” computes and displays speed and altitude of the vehicle all the time.


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