Monday, February 04, 2008

THE PUNCHED CARD (HOLLERITH CARD)

Ever seen a punched card? These were used as input media for first, second and third generation computers. I did my first computer programming course in 1980 at the Computer Society of India's Mhow Chapter which was housed in the Computer Wing of the Military College of Telecommunication Engineering Mhow. The computer we used was TDC - 316. The language I learnt was COBOL (Common Business Oriented Language). The programs we wrote were punched onto cards. There was one card per line of the program. Each line on a coding sheet could accomodate eighty characters. We would write our programs on coding sheets using a pencil. These sheets were then given to a punch operator to be converted into a deck of cards, one card per line of code. Each card could also hold eighty characters. If you peer at the fine print in the cards below (just below the first row of zeros) you can see a serial number list from 1 to 80.

When the programs were compiled by the computer they were checked for correct syntax. The error list was printed using the printer. If we found an error on, say, line 20 then that line was rewritten and a fresh card was punched for that line and inserted in the deck at the correct place. This process was repeated till all serious errors were removed and then the output was obtained. As the classes were held on alternate days it would often take upto a week to remove the errors and obtain the outputs.



In 1981 I used such cards again while learning another programming language named FORTRAN (Formula Translation). That was the last I used them. The code used to punch characters onto these cards is known as Hollerith code and I had memorised it. So I could 'read' a card fairly comfortably. In fact it was useful to show off in front of the girls who were doing the course with us.

It is mind boggling when I think of how computers have evolved in these twenty five years. In those days a select few could use these costly machines. Today almost everyone can thanks to the mouse and user friendly software.

I found these cards while sorting out old books. I have a few 'decks' of these cards lying in the garage. COBOL programs were long. So, if there were a hundred and twenty lines in a program the deck of cards which were punched would have an equal number of cards....

Let us see. It is possible that a few decades from today my nieces can sell these cards at some auction site and earn a few million dollars. That is one way of ensuring that they do not forget their crazy uncle...

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