CHAPTER 5
CENTRAL PROCESSING UNITS AND BUSES
INTRODUCTION
Digital computers have three major functional areas: central processing unit
(CPU), memory, and input/output (I/O). This applies whether the computer is
an 8-bit microprocessor or a 32-bit mainframe. Two other areas must be considered:
the system buses and the power supply. They, too, play a major role with the
functional areas of the computer. The buses are the means by which the CPU,
memory, and I/O communicate with each other. The power satisfies the dc voltage
requirements of the computer as you learned in chapter 4. Figure 5-1 shows a
typical block diagram of a computer. To complete the computer system, the
computer uses instructions to perform its operations. Through the man/machine
interfaces, you can control the computer’s operations to perform maintenance.
In this chapter, we discuss the CPU and buses. In chapter 6, we discuss memory.
In chapter 7, we discuss input/output and how the computer interfaces externally
with other computers, peripherals, and subsystems. In chapter 8, we examine
computer instructions and the man/machine interface.
You can find a computer’s functional areas and their operations, functional
descriptions, logic implementation, interpretation of logic, and functional
schematics in your computer’s technical maintenance or owner’s manuals. The
technical manuals and MRC documentation provide you information on the
required and/or recommended tools (standard and specialized), test documentation,
and test equipment to perform preventive maintenance. The technical manual or
owner’s manual documentation provides information to perform all aspects of
corrective maintenance. This includes test documentation and procedures; test
equipment; and tools for disassembly, assembly, and repair. Repair tools include
Figure 5-1.—Example of a typical block diagram of a computer.
5-1
