12
Pipelining
This chapter introduces the concept of pipeline architecture and discusses about its related
topics including its advantages and various types of hazards those may arise out of it. After
completion of this chapter, the reader would know about
R Basic concepts of pipeline architecture.
R Different types of hazards encountered during pipeline operations.
R Data paths and other essential features for implementing pipeline architecture.
R Techniques of enhancing pipeline performance, like out-of-order execution, register
renaming, speculative execution and so on.
R Performance of Pentium 4 pipeline.
C HAPTER OBJECTIVES
12.1 INTRODUCTION
Since its introduction, the major guiding factor for computer’s (or its processor’s) improvement and
enhancement was to make it perform faster. Indeed, at its early stage, the processor was an extremely
slow device as compared with the modern processors. Several factors were considered from those intro-
ductory days to enhance its performance by increasing its speed of execution. Some of these factors are:
R Increase of system clock speed.
R Widening the width of data bus, so that more number of bits may be processed at the same time.
R Reducing the number of instructions in the instruction set
R Adopting pipeline architecture.
The rst one, providing a faster system clock, encounters some dif culties related with heat-dissipation
and has to be solved in a different manner, which is beyond the scope of the present work. We have already
discussed about the effect of widening the data bus when discussed about Intel 8086 in Chapter 5. In
the same chapter, we have discussed about the advantage and limitations of RISC processors. However,
although we have introduced the term in Section 5.8.2, we have not explained the details of pipeline archi-
tecture in that chapter, which will be discussed in this chapter. We start the topic with the de nition of
pipeline architecture.
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