The IBM 1132 printer relies on the 1130 processor rather than internal logic to determine when to fire the print wheels as they rotated. Printers for the Model 4 run more slowly, but the slower processor still can not keep up with it. The hardware manual discloses that when the Model 4 was servicing the two highest-level interrupts (the level 0 card-reader column interrupt or the level 1 printer interrupt), it ran at the faster 3.6 µs cycle time. Some users of the Model 4 would write a phony printer driver that did not dismiss the printer interrupt, in order to benefit from the higher processor speed. However, lower-level interrupts are disabled during this interval, even the end-of-card interrupt (level 4) from the 1442 card reader.