RISC, or Reduced Instruction Set Computer. is a type of microprocessor architecture that utilizes a small, highly-optimized set of instructions, rather than a more specialized set of instructions often found in other types of architectures.

The first RISC projects came from IBM, Stanford, and UC-Berkeley in the late 70s and early 80s. The IBM 801, Stanford MIPS, and Berkeley RISC 1 and 2 were all designed with a similar philosophy which has become known as RISC. Certain design features have been characteristic of most RISC processors:

  • one cycle execution time: RISC processors have a CPI (clock per instruction) of one cycle. This is due to the optimization of each instruction on the CPU and a technique called ;

  • pipelining: a techique that allows for simultaneous execution of parts, or stages, of instructions to more efficiently process instructions;

  • large number of registers: the RISC design philosophy generally incorporates a larger number of registers to prevent in large amounts of interactions with memory
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We will first examine MIPS in detail as an example of an early RISC architecture to better understand the features and design of RISC architectures. We will then study pipelining to see the performance benefits of such a technique. Then we will look at the advantages and disadvantages of such a RISC-based architecture as compared to CISC architectures. Finally, we will discuss some of the recent developments and future directions of RISC processor technology in particular, and processor technology as a whole in general.

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