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. [Illustration: FIG. 3. Alphabetic punching.] [Illustration: 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. The numbers that are stored or sorted in punch-card machines may be of any size up to 80 digits, one in each column of the punch card. In doing arithmetic (adding, subtracting, multiplying, and dividing), however, the largest number of digits is usually 10. Beyond 10 digits, we can work out tricks in many cases. TYPES OF PUNCH-CARD MACHINES The chief IBM punch-card machines are: the _key punch_, the _verifier_, the _sorter_, the _interpreter_, the _reproducer_, the _collator_, the _multiplying punch_, the _calculating punch_, and the _tabulator_. Of these 9 machines, the last 6 have plugboards and can do many different operations as a result. There is a flow of punch cards through each of these machines. The machines differ from each other in the number and relation of the paths of flow, or _card channels_, and in the number and relation of the momentary stopping places, or _card stations_, at which cards are read, punched, or otherwise acted on. We can get a good idea of what a machine is from a picture of these card channels. Key Punch