Page 70 -

2.3 / THE EVOLUTION OF THE INTEL x86 ARCHITECTURE 45

design effort on complex instruction set computers (CISCs). The x86 incorporates
the sophisticated design principles once found only on mainframes and supercom-
puters and serves as an excellent example of CISC design. An alternative approach
to processor design in the reduced instruction set computer (RISC). The ARM ar-
chitecture is used in a wide variety of embedded systems and is one of the most
powerful and best-designed RISC-based systems on the market.
In this section and the next, we provide a brief overview of these two systems.
In terms of market share, Intel has ranked as the number one maker of micro-
processors for non-embedded systems for decades, a position it seems unlikely to
yield. The evolution of its flagship microprocessor product serves as a good indica-
tor of the evolution of computer technology in general.
Table 2.6 shows that evolution. Interestingly, as microprocessors have grown
faster and much more complex, Intel has actually picked up the pace. Intel used to
develop microprocessors one after another, every four years. But Intel hopes to
keep rivals at bay by trimming a year or two off this development time, and has
done so with the most recent x86 generations.
It is worthwhile to list some of the highlights of the evolution of the Intel prod-
uct line:

• 8080: The world’s first general-purpose microprocessor. This was an 8-bit ma-
chine, with an 8-bit data path to memory. The 8080 was used in the first per-
sonal computer, the Altair.
• 8086: A far more powerful, 16-bit machine. In addition to a wider data path
and larger registers, the 8086 sported an instruction cache, or queue, that
prefetches a few instructions before they are executed. A variant of this
processor, the 8088, was used in IBM’s first personal computer, securing the
success of Intel.The 8086 is the first appearance of the x86 architecture.
• 80286: This extension of the 8086 enabled addressing a 16-MByte memory in-
stead of just 1 MByte.
• 80386: Intel’s first 32-bit machine, and a major overhaul of the product.With a
32-bit architecture, the 80386 rivaled the complexity and power of minicom-
puters and mainframes introduced just a few years earlier. This was the first
Intel processor to support multitasking, meaning it could run multiple pro-
grams at the same time.
• 80486: The 80486 introduced the use of much more sophisticated and powerful
cache technology and sophisticated instruction pipelining. The 80486 also of-
fered a built-in math coprocessor, offloading complex math operations from
the main CPU.
• Pentium: With the Pentium, Intel introduced the use of superscalar tech-
niques, which allow multiple instructions to execute in parallel.
• Pentium Pro: The Pentium Pro continued the move into superscalar organiza-
tion begun with the Pentium, with aggressive use of register renaming, branch
prediction, data flow analysis, and speculative execution.
• Pentium II: The Pentium II incorporated Intel MMX technology, which is de-
signed specifically to process video, audio, and graphics data efficiently.