(the level 0 card-reader column interrupt or the level 1 printer interrupt), it ran at the faster 3.6 us 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.

Chronology

*February 11, 1965 - IBM introduces the 1130 (Models 1A, 1B, 2A,

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