CPUArchitecture - CPU Architecture 4.1 Chapter Overview...

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Page 234 CPU Ar chitecture Chapter Four 4.1 Chapter Overview This chapter discusses history of the 80x86 CPU family and the major improvements occuring along the line. The historical background will help you better understand the design compromises they made as well as under - stand the legacy issues surrounding the CPU s design. This chapter also discusses the major advances in com - puter architecture that Intel employed while improving the x86 1 . 4.2 The History of the 80x86 CPU Family Intel developed and delivered the first commercially viable microprocessor way back in the early 1970 s: the 4004 and 4040 devices. These four -bit microprocessors, intended for use in calculators, had very little power . Nevertheless, they demonstrated the future potential of the microprocessor — an entire CPU on a single piece of silicon 2 . Intel rapidly followed their four -bit of ferings with their 8008 and 8080 eight-bit CPUs. A small outfit in Santa Fe, New Mexico, incorporated the 8080 CPU into a box they called the Altair 8800. Although this was not the world s first "personal computer" (there were some limited distribution machines built around the 8008 prior to this), the Altair was the device that sparked the imaginations of hobbyists the world over and the personal computer revolution was born. Intel soon had competition from Motorola, MOS T echnology , and an upstart company formed by disgrunt - eled Intel employees, Zilog. T o compete, Intel produced the 8085 microprocessor . T o the software engineer , the 8085 was essentially the same as the 8080. However , the 8085 had lots of hardware improvements that made it easier to design into a circuit. Unfortunately , from a software perspective the other manufacturer s of ferings were better . Motorola s 6800 series was easier to program, MOS T echnologies 65xx family was easier to pro - gram and very inexpensive, and Zilog s Z80 chip was upwards compatible with the 8080 with lots of additional instructions and other features. By 1978 most personal computers were using the 6502 or Z80 chips, not the Intel of ferings. Sometime between 1976 and 1978 Intel decided that they needed to leap-frog the competition and produce a 16-bit microprocessor that of fered substantially more power than their competitor s eight-bit of ferings. This ini - tiative led to the design of the 8086 microprocessor . The 8086 microprocessor was not the world s first 16-bit microprocessor (there were some oddball 16-bit microprocessors prior to this point) but it was certainly the high - est performance single-chip 16-bit microprocessor when it was first introduced. During the design timeframe of the 8086 memory was very expensive. Sixteen Kilobytes of RAM was sell - ing above $200 at the time. One problem with a 16-bit CPU is that programs tend to consume more memory than their counterparts on an eight-bit CPU. Intel, ever cogniscent of the fact that designers would reject their CPU if the total system cost was too high, made a special ef fort to design an instruction set that had a high mem - ory density (that is, packed as many instructions into as little RAM as possible).
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CPUArchitecture - CPU Architecture 4.1 Chapter Overview...

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