The Programming Model and the ISA

Back in the bad old days, programmers had to enter programs into the computer directly in machine language (after having walked five miles in the snow uphill to work). In the very early stages of computing, this was done by flipping switches. The programmer toggled strings of 1s and 0s into the computer’s very limited memory, ran the program, and then pored over the resulting strings of 1s and 0s to decode the answer.

Once memory sizes and processing power increased to the point where programmer time and effort were valuable enough relative to computing time and memory space, computer scientists devised ways of allowing the computer to use a portion of its power and memory to take on some of the burden of making ...

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