We introduced RISC architectures in the context of some example systems in Chapter 4. RISC is not so much an architecture as it is a design philosophy. Recall that RISC machines are so named because they originally offered a smaller instruction set as compared to CISC machines. As RISC machines were being developed, the term “reduced” became somewhat of a misnomer, and is even more so now. The original idea was to provide a set of minimal instructions that could carry out all essential operations: data movement, ALU operations, and branching. Only explicit load and store instructions were permitted access to memory.

Complex instruction set designs were motivated by the high cost of memory. Having more complexity packed ...

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