Computers as Components, 2nd Edition

92 CHAPTER 3 CPUs

Status

register

Data

register

Device

mechanism

CPU

FIGURE 3.1

Structure of a typical I/O device.

3.1.1 Input and Output Devices

Input and output devices usually have some analog or nonelectronic component—

for instance, a disk drive has a rotating disk and analog read/write electronics. But

the digital logic in the device that is most closely connected to the CPU very strongly

resembles the logic you would expect in any computer system.

Figure 3.1 shows the structure of a typical I/O device and its relationship to the

CPU.The interface between the CPU and the device’s internals (e.g.,the rotating disk

and read/write electronics in a disk