The principles of computer hardware

The faculty of each university selects its own set of topics for inclusion in an introductory course on computer architecture and digital systems. Some courses emphasize digital design and Boolean algebra. Some emphasize computer architecture (the assembly language programmer's view of a computer), and some emphasize the other elements of a computer (memory, peripherals, and computer communications). A prior knowledge of computer science is not required for entry to many courses in universities, and this book is therefore written for those with no previous knowledge of computer science. Because students following a course in computer science or computer technology will also be studying programming in a high-level language, no attempt is made to teach programming in a highlevel language, and we assume that the reader is familiar with the concepts underlying a high-level language.

I've also broadened the range of topics normally found in first-level courses in computer hardware and provided sections introducing operating systems and local area networks, as these two topics are so intimately related to the hardware of the computer. Like most introductory books on computer architecture, I have chosen a specific microprocessor as a model. The ideal computer architecture is both powerful (rich in features) and yet easy to understand without exposing the student to a steep learning curve. Some microprocessors have very complicated architectures that confront students with too much fine detail early in their course. I would emphasize that this book isn't designed to provide a practical course in assembly language programming on the 68000. By the way, you will see the words computer, CPU, processor, microprocessor, and microcomputer in this and other texts. The part of a computer that actually executes a program is called a CPU (central processing unit) or more simply a processor. A computer that is constructed around a microprocessor can be called a microcomputer.

We've already said that this book provides a traditional introductory course in computer architecture plus additional material to broaden its scope and fill in some of the gaps left in such courses. Because students following an introductory course might find it difficult to distinguish between foreground and background material, the following guide might help to indicate the more fundamental components of the course.

• Chapter 2
  The vast majority of Chapter 2 deals with essential topics such as gates, Boolean algebra, and Karnaugh maps. Therefore this chapter is essential reading.
• Chapter 3
  In this chapter we demonstrate how to design the sequential circuits required to construct a computer. We first introduce the bistable (flip-flop) used to construct sequential circuits, which requires a quantum jump in understanding over earlier sections on gates and similar logic elements. Introductory texts on computer organization often cover only the basic idea of the flip-flop and its application as a storage element in registers and counters. Students are expected to be able to design moderately complex circuits built from gates, but are expected only to appreciate the role of sequential circuits.
• Chapter 4
  This chapter deals with the way in which numbers are represented inside a computer and the way in which they are manipulated in simple arithmetic operations. Apart from some of die coding theory and details of multiplication and division, almost all of this chapter is essential reading. Section 4.8 on floating point arithmetic goes into more detail than some other texts because a few students have difficulty in understanding how floating point numbers are represented and manipulated. The final part of Chapter 4 introduces multiplication and division and describes how these operations are actually carried out inside computers. Multiplication and division can be omitted if the student is not interested in how these operations are implemented.
• Chapter 5
  This is the heart of the book and is concerned with the structure and operation of the computer itself. The section dealing with the operation of the computer's control unit that decodes and executes instructions may be omitted on a first reading. The control unit is normally encountered in a second- or third-level course, but has been included here for the purpose of completeness and to provide an insight into how the computer actually turns a binary-coded instruction into a sequence of events that carry out the instruction.
• Chapter 6
  Having introduced the architecture of a CPU we include an overview of assembly language programming and the design of simple 68000 assembly language programs. This chapter relies heavily on the 68000 cross-assembler and simulator provided with the book. You can use this software to investigate the behavior of the 68000 on a PC. Readers interested only in the structure of the CPU may omit this chapter.
• Chapter 7
  The previous two chapters have concentrated on a popular CISC (complex instruction set computer). In this chapter we look at the trend in computer architecture towards greater simplicity and introduce the RISC or reduced instruction set computer architecture, which achieves a high level of performance by overlapping the various stages in the execution of an instruction. We look at the ARM family of processors and introduce the software package that enables you to write programs for an ARM and to run them. on a PC.
• Chapter 8
  This chapter deals with input/output techniques and peripherals such as printers and CRT terminals that enable the computer to communicate with the external world. We are interested in two aspects of an interface: the way in which information is transferred between a computer and peripherals, and the peripherals themselves. We also take a look at some of the interface chips that facilitate the connection of the computer to its peripherals. The final part of this chapter describes sortie of the peripherals that you would find in a typical PC (keyboard, display, printer, and mouse). We also look at some of the more unusual peripherals that, for example, can measure how fast a body is rotating. Input/output techniques are essential reading and should not be left out, although the details of the serial and parallel interfaces may be omitted.
• Chapter 9
  Information isn't stored in a computer in just one type of storage device. It's stored in DRAM, on disk, on CDROM, and on tape. This chapter examines the operating principles and characteristics of some of the storage devices found in a computer. There's a lot of detail in this chapter. Some readers may wish to omit the design of memory systems (for example, address decoding and interfacing) and just concentrate on the reasons why computers have so many different types of memory.
• Chapter 10
  Some topics in computer architecture can be placed under more than one heading. In this chapter we deal with hardware topics that are closely related to the computer's operating system. The two most important elements of a computer's hardware that concern the operating system are multiprogramming and memory management. These topics are intimately connected with interrupt handling and data storage techniques and serve as practical examples of the use of the hardware described in Chapters 8 and 9. We also look at one of the more sophisticated memory topics: the use of cache memory to enhance a computer's performance. Those who require a basic introduction to computer hardware may omit this chapter, although it best illustrates how hardware and software come together in the operating system.
• Chapter 11
  The techniques used to link computers to create computer networks are not normally covered by first-level texts on computer architecture. However, the growth of both local area networks and the Internet have propelled computer communications to the forefront of computing. For this reason we would expect students to read this chapter even if some of it falls outside the scope of their syllabus.
• Chapter 12
  The final chapter looks at several of the more advanced topics that we omitted from earlier chapters. The first topic concerns the electrical behavior of practical gates - real gates consume power and delay signals and we have to take account of these effects. The second topic deals with die reliability of systems-the designer needs to be able to predict how reliable his or her system is likely to be. Moreover, the designer sometimes needs to enhance the reliability of a system when it is used in an important application. The final topic concerns the way in which analog signals are converted into digital form and vice versa. We also demonstrate how a computer can process digital signals to perform control functions and signal processing.