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Learning Computers – 1965

  David B. Tuttle, Principal Engineer  
  Dave.Tuttle@alum.mit.edu  

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IBM 1620  

IBM 1620 Model 1

  • IBM type-bar electric typewriter for a system console
  • 64,000 memory locations (with memory expansion unit)
  • Variable word-length, decimal arithmetic, Hollerith encoding
  • 80-column punch card reader / punch for input/output

This is the first machine I learned to program, at Stevens Institute of Technology in Hoboken, New Jersey.  The National Science Foundation sponsored a variety of summer opportunities for high school students, Secondary Science Training Programs (SSTP).  One of my brother's friends had attended a computer-based program at Carnegie Mellon University in Pittsburgh.  When I applied for the Carnegie program in 1965 it was already full, but I found out about a similar one at Stevens and was accpeted there. 

The six-week program had us staying in undergraduate dormitory rooms on campus.  Classroom study was split between Abstract Algebra and Computers.  The first day classwork for computers was to buy the IBM 1620 Fortran II manual at the campus store and read the first half, up to the 'DO loops' section, ready for discussion the second day. 

Programs were written out on coding sheets and punched into cards, using the fixed-column format for Fortran II.  For test runs, the Fortran compiler was loaded into the card reader, followed by a program input card deck.  The first 20 or 30 columns of the input cards were left blank, to leave room for the compiler results.  The output was punched into cards, which then had to be fed into the IBM 407 Accounting Machine to generate a listing.  When you made a mistake in the input coding, the error message(s) showed up instead of your program. 

When your program did compile successfully, the first columns of the output cards contained the (decimal) machine code, which then could be executed by putting them back into the card reader behind a program loader. 

Repeat as necessary.  Program results came out as cards, of course, so they had to be printed before you (finally) got an answer.


At the end of that summer, I had a few chances to try out my programs on another IBM 1620 and, using IBM's Autocoder language, on an IBM 1410.  The same home-town friend who attended the Carnegie program had a summer job as a computer operator at the New York Downstate Medical Center on Long Island, an easy ride from Pelham Manor.  My career adventure had begun.

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Copyright 2016 by David B. Tuttle, Reading MA
This page updated 26-Dec-2015

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