Day 6: Punch Cards

Punch cards were an IBM invention used in early mainframe computers, banks, instruments, textile looms, etc. for permanent data storage. They are pieces of stiff paper with 80 columns of 12 rows, and they can be read according to the presence or absence of holes. To read a punch card, you must understand that each column represents one figure. Start with the leftmost column and decipher rightward.



Consult the key above for a visual aid:

-If there is only one punch in the column, the data represents the NUMBER that is punched.
-If there are two punches in the column, the data represents a LETTER.
-As you can see on the key, one of the punches will be in the top margin, and another will be
on a number. There are two possible levels for the punches in the top margin, and the
the row with 0s also serves to show letters. Three levels are necessary because there are 9 rows, therefore each level can only stand for 9 letters. The first tier represents A-I. Each of these letters has a numeric value 1-9. (For example, A=1, B=2, C=3...I=9. Therefore, if there is a punch in the top line of the top margin, and a second punch on the number 3, the data is "C".) The second line in the margin stands for letters J through R. Again, each of these letters is assigned a value 1-9. If there is a punch on the second blank line and the number 1, the data is "J". Finally, punches on 0 represent the rest of the alphabet (unless only 0 is punched, in which case the data is 0.)
-If there are three punches in the column, including one in the top three lines (like the alphabet), one number, and one "8", this represents a symbol. The system is the same as the alphabet. Consult the key for how to represent each symbol. (example: a period is top row in the margin, 3, and 8.)