The Univac Solid State Computer 90, our projects.

Rob Weemhof (on the right) and Jan Lindeboom.

Our projects.

Initially this large machine was intended as an educational project for our school. 
Years before the first microcomputers became available, we taught ourselves to program, 
to repair and to understand the logical-circuitry of one of the first commonly available digital computers. 
We made some hardware alterations:

We owned two Card Readers and Huib changed in one reader the circuitry of the reading stations, 
to make them reading cards with pencil-marks. 
This worked well, but while this was meant to process the examinations, 
we never succeeded in working out the whole project to be sufficiently reliable.

At the beginning we had to build in another magnetic drum memory, because the original drum was sold to a Russian company. 
The new one worked well in the CPU, but since it was written to control equipment in an industrial surrounding, 
it was not capable of controlling the punchcard devices. 
I wrote the missing information on a tape-buffer-band which was not used, by wiring it as a normal memory-band. 
I built a digital-switch that altered reading between the timing-band and the tape-buffer in such way 
that only the addresses of the original timingband were used and the other 8 digits were used from this buffer-band.
This project was successful, from then onwards all cardequipment could be used.


The new-build digital switch for the timingband

On the right: the added circuitboards

We programmed some software applications, one was to print addresses for a society of school-teachers.
We programmed some simple mathematical problems, to demonstrate the power of our machine. 
I wrote a program to print a table of powers of a number, until the results printed, occupied the full print-line of 130 digits.

I also wrote a program to print a table of primes. It did well but I never had it run till the end. 
Theoretically it could find primes till the value of 900,000,000 and it would have taken centuries to finish.

After I left this school I used the computer to programm an interpretor for generating, processing and printing graphic art, 
to be used by artists. The program worked well but I never used it in practice, since I started then in a new occupation. 

    Examples of tests of the graphical-art program.


And of course we wrote many small programs to test the USSC and even programs to make music. 
We found many ways to feed the equipment with special orders of punched cards to force them to operate in specific rhythms. 
I wrote a program for a controlled firing of the hammers of the print-mechanism to generate tones in the range of 1KHz to 10 Hz.

With a amplifier connected to a single bit of register C, we could hear and recognize loops in the executed program.

Once I took out a circuitboard with an amplifier for the magnetic print-drum, on which all printable-characters were coded. 
One of the capacitors must still have been loaded, because after replacing the amplifier, the printer-hardware refused to work. 
Then I discovered that my action had caused a spike to be written on this magnetic print-drum. 
With the help of a oscilloscope, a stroboscope and some marks on the print-cylinder, I determed, 
while it was rotating, the exact position of the cylinder, similar to when I took the amplifier out (= the place of the spike).  
I halted the printer and connected an one meter metal bar which I had borrowed from the chemistry lab, 
to the shaft of the print-cylinder and set a small 100 kHz signal on the corresponding magnetic head. 
Then, by moving the bar a few times, less then a centimeter, I wiped out the erroneous spike from the code-drum. 
After this, the printer worked as normal.

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