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Unformatted text preview: ic task, over and over and over: It reads the instruction from memory pointed at by the program counter (PC), interprets the bits in the instruction, performs some simple operation dictated by the instruction, and then updates the PC to point to the next instruction, which may or may not be contiguous in memory to the instruction that was just executed. There are only a few of these simple operations, and they revolve around main memory, the register ﬁle, and the arithmetic/logic unit (ALU). The register ﬁle is a small storage device that consists of a collection of word-sized registers, each with its own unique name. The ALU computes new data and address values. Here are some examples of the simple operations that the CPU might carry out at the request of an instruction: ¯ ¯ ¯ ¯
1 Load: Copy a byte or a word from main memory into a register, overwriting the previous contents of the register. Store: Copy the a byte or a word from a register to a location in main memory, overwriting the previous contents of that location. Update: Copy...
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- Spring '10
- The American