Fig. 2. Scheme of standard punch card.
(Note: Positions 11 and 12 are not usually marked by printed numbers or letters.)
The standard IBM punch card of today has 80 columns and 12 positions for punching in each column ([Fig. 2]). A single punched hole in each of the positions known as 0 to 9 stands for each of the digits 0 to 9 respectively. The remaining 2 single punch positions available in any column are usually called the 11 position and 12 position (though sometimes called the numerical X position and Y position). These two positions do not behave arithmetically as 11 and 12. Actually, in the space between one card and the next card as they are fed through the machines, more positions occur. For example, there may be 4 more: a 10 position preceding the 9, and a 13, a 14, and a 15 position following the 12. The 16 positions in total correspond to a full turn, 360°, of the roller under the brush, and to a complete cycle in the machine; and a single position corresponds to ¹/₁₆ of 360°, or 22½°. In some machines, the total number of positions may be 20. A pair of punches stands for each of the letters of the alphabet, according to the scheme shown.
| A | 12-1 | J | 11-1 | Unused | 0-1 |
| B | 12-2 | K | 11-2 | S | 0-2 |
| C | 12-3 | L | 11-3 | T | 0-3 |
| D | 12-4 | M | 11-4 | U | 0-4 |
| E | 12-5 | N | 11-5 | V | 0-5 |
| F | 12-6 | O | 11-6 | W | 0-6 |
| G | 12-7 | P | 11-7 | X | 0-7 |
| H | 12-8 | Q | 11-8 | Y | 0-8 |
| I | 12-9 | R | 11-9 | Z | 0-9 |
For example, the word MASON is shown punched in [Fig. 3].
Fig. 3. Alphabetic punching.
Fig. 4. Single-panel plugboard.
To increase the versatility of the machines and provide them with instructions, many of them have plugboards ([Fig. 4]). These are standard interchangeable boards filled with prongs on one side and holes or terminals called hubs on the other side. The side with the prongs connects to the ends of electrical circuits in the punch-card machine, which are brought together in one place for the purpose. On the other side of the board, using plugwires, we can connect the hubs to each other in different ways to produce different results. The single-panel plugboard is 10 inches long and 5¾ inches wide. It contains 660 hubs in front and 660 corresponding prongs in the back. A double-panel plugboard or a triple-panel plugboard applies to some machines. In less time than it takes to describe it, we can take one wired-up plugboard out of a machine and put in a new wired-up plugboard and thus change completely the instructions under which the machine operates. Many of the machines have a number of different switches that we must also change, when going from one kind of problem to another.