Historical Notes

Before ending, we include a brief historical note on the origin of some of the fundamental ideas discussed in this chapter. If you are interested in learning more, read Smotherman’s excellent summary“Interrupts” by Mark Smotherman. July ’08. Available: http://people.cs.clemson.edu/ ̃mark/interrupts.html. A treasure trove of information on the history of interrupts, DMA, and related early ideas in computing..

• Interrupts are an ancient idea, existing on the earliest of machines. For example, the UNIVAC in the early 1950s had some form of interrupt vectoring, although it is unclear in exactly which year this feature was available“Interrupts” by Mark Smotherman. July ’08. Available: http://people.cs.clemson.edu/ ̃mark/interrupts.html. A treasure trove of information on the history of interrupts, DMA, and related early ideas in computing.. Sadly, even in its infancy, we are beginning to lose the origins of computing history.

• There is also some debate as to which machine first introduced the idea of DMA. For example, Knuth and others point to the DYSEAC (a “mobile” machine, which at the time meant it could be hauled in a trailer), whereas others think the IBM SAGE may have been the first“Interrupts” by Mark Smotherman. July ’08. Available: http://people.cs.clemson.edu/ ̃mark/interrupts.html. A treasure trove of information on the history of interrupts, DMA, and related early ideas in computing.. Either way, by the mid ’50s, systems with I/O devices that communicated directly with memory and interrupted the CPU when finished existed.

• The history here is difficult to trace because the inventions are tied to real, and sometimes obscure, machines. For example, some think that the Lincoln Labs TX-2 machine was first with vectored interrupts“Interrupts” by Mark Smotherman. July ’08. Available: http://people.cs.clemson.edu/ ̃mark/interrupts.html. A treasure trove of information on the history of interrupts, DMA, and related early ideas in computing., but this is hardly clear.

Because the ideas are relatively obvious — no Einsteinian leap is required to come up with the idea of letting the CPU do something else while a slow I/O is pending — perhaps our focus on “who first?” is misguided. What is certainly clear: as people built these early machines, it became obvious that I/O support was needed. Interrupts, DMA, and related ideas are all direct outcomes of the nature of fast CPUs and slow devices; if you were there at the time, you might have had similar ideas.