4.9   INSTRUCTION PROCESSING

Now that we have a basic language with which to communicate ideas to our computer, we need to discuss exactly how a specific program is executed. All computers follow a basic machine cycle: the fetch, decode, and execute cycle.

4.9.1   The Fetch–Decode–Execute Cycle

The fetch–decode–execute cycle represents the steps that a computer follows to run a program. The CPU fetches an instruction (transfers it from main memory to the instruction register), decodes it (determines the opcode and fetches any data necessary to carry out the instruction), and executes it (performs the operation[s] indicated by the instruction). Notice that a large part of this cycle is spent copying data from one location to another. When ...

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