CHAPTER 8 - The 80486 and Pentium

Abstract

In 1989, Intel announced the 80486 processor. There were no significant changes to the instruction set. The popularity of the Intel architecture had dictated the future for the 80×86 instruction set and the rules were clear: (1) no major instruction set changes were needed; (2) even if changes were made, no one would use them for fear of being incompatible with the installed base; and (3) performance gains would come mostly from hardware changes, not software. However, the internal architecture of the 486 is vastly different from that of prior processors. Reduced instruction set computing (RISC) design techniques were employed, including the use of a five-stage instruction pipeline and on-chip cache memory. The floating-point processor, a separate chip on the 8088 through 80386, is on the same chip, allowing for faster operation. The six new instructions are primarily for use in operating-system software. This chapter discusses the first three of these instructions that any application program can use them. In 1993, Intel announced the Pentium processor. There are several major changes that make the Pentium significantly faster than the 486. The primary change is that there are two integer pipelines that can be used to simultaneously execute two instructions.