Essential Guide to Computing: The Story of Information Technology, The

The Internal Operations of the CPU

As noted earlier, the CPU is also called a microprocessor because all of its components—at least all those needed to carry out calculations—are on a single silicon chip (see Chapter 4 for a discussion of how chips are made). We'll begin our overview of the microprocessor with a simple description of its functions. The classical CPU includes a four-sequence operation (see Figure 1.4).

1. Fetch

2. Decode

3. Execute

4. Store

Fetch

First, instructions and data are fetched from outside the chip (usually this means from DRAM). An example of an instruction is one that contains a simple mathematical operation such as "add." In some cases, the data used by an instruction are included with it; in other instances, the instruction references ...