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Paper Tape Computers

May 11, 2013

This all happened in the early 1960’s when I was in Science at university.  One mathematics course was taught by an Engineering professor.  I enjoyed that course because it was full of surprises, all about areas of mathematics that I’d never encountered before.  At one point, the professor told us about binary, octal, and hexadecimal numbers.  Then he began describing the Bendix computer.  That was completely unexpected to me.  He told us it was grey, in the shape and size of a refrigerator.  It used a rotating drum memory, with a series of read/write heads arranged across the drum.  Each head had access to one track on the drum.  Each track was divided into memory cells.  Each memory cell had an address of its own.  They could contain either data or a machine instruction.  We learned to write simple programs in machine code, following the instruction chart he handed out.

Then the professor took us to see the Bendix.  It was at the far end of a narrow room in the Engineering building.  It was indeed a grey rack.  I recognized the paper tape reader near the top of the front panel  The console, on a nearby desk, was a model 19 Teletype machine.  It used a narrow grey five-level paper tape.  The professor demonstrated how to load a small machine language program from paper tape and how to run it, with output on the console.  He told us that it was used constantly by Engineering faculty and students, and also by a local company for transformer designs.

I also went to an evenng course taught by an IBM representative.  He taught us Fortran in the first few sessions and then took us to see the IBM computer.  It was in the same room as the Bendix, but closer to the door.  It was about the size and shape of a desk, with lights on the front panel that showed the memory address in binary.  This one used a wider yellow eight-level paper tape.  The console was an IBM Selectric typewriter.  The IBM representative pressed the reset button and then loaded the compiler from a reel of paper tape.  Reading all that tape took some time, possibly ten minutes.  Then he asked if anyone had a Fortran program that they wanted to run.  Nobody had one except me.  I had written one that identified and printed prime numbers.  He asked me to type it in on the console.  I tried, but I didn’t know how to type at that time.  I made lots of mistakes.  With every mistake, the compiler crashed and had to be reloaded from paper tape.  This was embarrassing.  I felt that I was responsible for wasting every body else’s time.  Finally, he said that he would type it in instead of me.  Once again, the compiler crashed.  At least it wasn’t me that time, although it was my program.  Then he read over my five-line program and told me that one statement wouldn’t work with that compiler.  He explained that he was using the Gotran compiler because it was smaller and quicker to load.  That statement only worked with the full Fortran compiler.  He gave up on mine and typed in his own short program.  That one actually worked.  We finally got our demonstration of a program on the IBM computer.  As I recall, it printed one line on the console.

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