Animation of the print train on the IBM 1403 N1 printer

In 1959, IBM introduced the 1401 computer, connected to the high-speed 1403 line printer. In the 1960s, IBM produced a faster version of the 1403 printer, known as the N1. This printer used a "train" of type slugs rather than a rotating chain, allowing it to print 1100 lines per minute instead of 600. The printer had 132 print columns, with a hammer at each position. The train had type elements corresponding to the 48 printable characters. As the appropriate type element passed a hammer, the hammer could fire to drive the type element against the ribbon and paper, printing the character.

The animation below shows how the hammers (green) interact with the train (blue) as the train slowly moves to the left. When a hammer is aligned with a train element and can print the character, the elements turn red. The numbers above the hammers show the hammer number from 1 to 132. The numbers below the train show the train element number. Below that is the character printed by each train element.

Each step of the animation corresponds to 5.0 microseconds of real time during which the train moves 0.001 inches. The slow setting is 100,000 times slower than real life, while the fast setting is 3000 times slower than real life. Printing a line requires 48 scans in total.

(Click Slow to slow down the animation.)

The timing between the hammers and the rotating train is tricky to understand. The spacing between the train and the hammers is very slightly (0.001 inches) more than a 3:2 ratio, so a tiny movement of the train changes the aligned elements. One hammer at a time is aligned with a type element, giving it the option to fire and print a character. As the train moves, a new hammer and type element are aligned. Due to the spacing, every third hammer will line up with every second type element in sequence. After 44 (one third) of the hammers have lined up, one print subscan is completed. Three print subscans give each hammer a chance to print a character, forming a print scan. Since there are 48 characters, 48 print scans are required to print a full line. The train moves very fast (206 inches per second) and a full line requires just 32 milliseconds to print (details).