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Chapter Review

In this chapter, we have examined the fundamental structure of computers. A computer, like many digital systems, consists of data-path and control. The data-path contains the storage elements (registers) that hold operands, the functional units (ALUs, shifter registers) that operate on data, and the interconnections (buses) between them.

The computer's control is nothing more than a finite state machine. It cycles through a collection of states that fetch the next instruction from memory, decode this instruction to determine its type, and then execute the instruction. The control executes the instruction by asserting signals to the data-path to cause it to move data from registers to functional units, perform operations, and return the results to the registers.

Register transfer operations provide a notation for describing functional unit operations and the data movements between registers and functional units. The register transfer operations are normally written in a form that is independent of the detailed interconnections supported by the data-path.

Once the data-path interconnections are determined, we replace each register transfer operation by a sequence of microoperations. These correspond to detailed control signals to the data-path that must be asserted to cause a register transfer operation to take place.

Computers are interesting because they are particularly complex digital hardware systems. The data-path is not where this complexity comes from. It comes from the control portion of the machine. In the next chapter, we will look at ways to organize the complex control state machine of a digital computer.

Further Reading

Unfortunately, most textbooks on logic design do not provide much coverage on computer organization. After all, a detailed treatment of computer architectures, instruction sets, and their implementation is a topic for another book. Notable exceptions include Johnson and Karim, Digital Design: A Pragmatic Approach, PWS Engineering, Boston, 1987, and Prosser and Winkel, The Art of Digital Design, 2nd ed., Prentice-Hall, Englewood Cliffs, NJ, 1987. Both of these have several chapters on computer structures and their implementations in hardware.

For a historical perspective on how computer architectures have developed, a wonderful book is D. Patterson and J. Hennessy, Computer Architecture: A Quantitative Approach, Morgan-Kaufmann, Redwood City, CA, 1990.

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This file last updated on 07/16/96 at 04:05:25.
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