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MODERN PROCESSOR DESIGN AND OPERATION
One important concept is that the actual way a modern
processor operates can be quite different from the model of
computation implied by the ISA. The ISA model would seem to
imply sequential instruction execution, where each instruction is
fetched and executed to completion before the next one begins. By
executing different parts of multiple instructions simultaneously, the
processor can achieve higher performance than if it executed just one
instruction at a time. Special mechanisms are used to make sure the
processor computes the same results as it would with sequential
execution. This idea of using clever tricks to improve performance
while maintaining the functionality of a simpler and more abstract
model is well known in computer science.
Chances are you will never design your own processor. This is
a task for experts working at fewer than 100 companies worldwide.
Why, then, should you learn about processor design?
• It is intellectually interesting and important. There is an intrinsic
value in learning how things work.
It is especially interesting to learn the inner workings of a
system that is such a part of the daily lives of computer scientists and
engineers and yet remains a mystery to many. Processor design
embodies many of the principles of good engineering practice. It
requires creating a simple and regular structure to perform a complex
task.
• Understanding how the processor works aids in understanding how
the overall computer system works.
Although few people design processors, many design hardware
systems that contain processors. This has become commonplace as
processors are embedded into real-world systems such as
automobiles and appliances. Embedded-system designers must
understand how processors work, because these systems are

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