Evolution of Microprocessor
It is interesting to note that the microprocessor had existed for only 10 years prior to the creation of the PC! Intel invented the microprocessor in 1971; the PC was created by IBM in 1981. Now more than 20 years later, we are still using systems based more or less on the design of that first PC. The processors powering our PCs today are still backward compatible in many ways with the 8088 that IBM selected for the first PC in 1981. November 15, 2001 marked the 30th anniversary of the microprocessor, and in those 30 years processor speed has increased more than 18,500 times (from 0.108MHz to 2GHz).The 4004 was introduced on November 15, 1971 and originally ran at a clock speed of 108KHz (108,000 cycles per second, or just over one-tenth a megahertz). The 4004 contained 2,300 transistors and was built on a 10-micron process. This means that each line, trace, or transistor could be spaced about 10 microns (millionths of a meter) apart. Data was transferred 4 bits at a time, and the maximum addressable memory was only 640 bytes. The 4004 was designed for use in a calculator but proved to be useful for many other functions because of its inherent programmability. For example, the 4004 was used in traffic light controllers, blood analyzers, and even in the NASA Pioneer 10 deep space probe! In April 1972, Intel released the 8008 processor, which originally ran at a clock speed of 200KHz (0.2MHz). The 8008 processor contained 3,500 transistors and was built on the same 10-micron process as the previous processor. The big change in the 8008 was that it had an 8-bit data bus, which meant it could move data 8 bits at a timetwice as much as the previous chip. It could also address more memory, up to 16KB. This chip was primarily used in dumb terminals and general-purpose calculators. The next chip in the lineup was the 8080, introduced in April 1974, running at a clock rate of 2MHz. Due mostly to the faster clock rate, the 8080 processor had 10 times the performance of the 8008. The 8080 chip contained 6,000 transistors and was built on a 6-micron process. Similar to the previous chip, the 8080 had an 8-bit data bus, so it could transfer 8 bits of data at a time. The 8080 could address up to 64KB of memory, significantly more than the previous chip. It was the 8080 that helped start the PC revolution because this was the processor chip used in what is generally regarded as the first personal computer, the Altair 8800. The CP/M operating system was written for the 8080 chip, and Microsoft was founded and delivered its first product: Microsoft BASIC for the Altair. These initial tools provided the foundation for a revolution in software because thousands of programs were written to run on this platform. In fact, the 8080 became so popular that it was cloned. A company called Zilog formed in late 1975, joined by several ex-Intel 8080 engineers. In July 1976, it released the Z-80 processor, which was a vastly improved version of the 8080. It was not pin compatible but instead combined functions such as the memory interface and RAM refresh circuitry, which enabled cheaper and simpler systems to be designed. The Z-80 also incorporated a superset of 8080 instructions, meaning it could run all 8080 programs. It also included new instructions and new internal registers, so software designed for the Z-80 would not necessarily run on the older 8080. The Z-80 ran initially at 2.5MHz (later versions ran up to 10MHz) and contained 8,500 transistors. The Z-80 could access 64KB of memory. RadioShack selected the Z-80 for the TRS-80 Model 1, its first PC. The chip also was the first to be used by many pioneering systems, including the Osborne and Kaypro machines. Other companies followed, and soon the Z-80 was the standard processor for systems running the CP/M operating system and the popular software of the day. Intel released the 8085, its follow-up to the 8080, in March 1976. Even though it predated the Z-80 by...
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