Enigma : The Microprocessor

The Enigma: The Microprocessor

Inside of the mysterious box that perches ominously on your desk is one of the marvels of the modern world. This marvel is also a total enigma to most of the population. This enigma is, of course, the microprocessor. To an average observer a microprocessor is simply a small piece of black plastic that is found inside of almost everything.

In How Microprocessors Work they are defined as a computer's central processing unit, usually contained on a single integrated circuit (Wyant and Hammerstrom, 193). In plain English this simply means that a microprocessor is the brain of a computer and it is only on one chip. Winn L. Rosch compares them to being an electronic equivalent of a knee-joint that when struck with the proper digital stimulus will react in the exact same way each time (Rosch,37). More practically a microprocessor is multitudinous transistors squeezed onto as small a piece of silicon as possible to do math problems as fast as possible.

Microprocessors are made of many smaller components which all work together to make the chip work. A really good analogy for the way the inner workings of a chip operate can be found in How Microprocessors Work. In their book, Wyant and Hammerstrom describe a microprocessor as a factory and all of the inner workings of the chip as the various parts of a factory (Wyant and Hammerstrom, 71-103). Basically a microprocessor can be seen as a factory because like a factory it is sent something and is told what to do with it. The microprocessor factory processes information. This most basic unit of this information is the bit. A bit is simply on or off. It is either a one or a zero. Bits are put into 8 bit groups called bytes. The number 8 is used because it is offers enough combinations to encode our entire language (2^8=256). If only 4 bits are used only (2^4=16) combinations would be possible. This is enough to encode 9 digits and some operations. (The first microprocessors powered calculators) A half byte is called a nibble and consists of 4 bits. In the world of computer graphics the combination of bits is easier seen. In computer graphics bits are used to make color combinations, thus with more bits more colors are possible. Eight bit graphics will display 256 colors, 16 bit will display 65,536, and 24 bit graphics will display 16.7 million colors. The bus unit is described as the shipping dock because it controls data transfers, and functions between the individual pieces of the chip. The part of the chip that performs the role of a purchasing department is called the prefetch unit. It's job is to make certain that enough data is on hand to keep the chip busy. The decode unit performs the role of a receiving department. It breaks done complicated instructions from the rest of the computer into smaller pieces that the chip can manipulate more readily. The control unit is compared to the person who oversees the workings of the entire factory. It is the part of the chip that keeps all the other parts working together and coordinates their actions. The arithmetic logic unit is compared to the assembly line of the factory. It is the part of the microprocessor that performs the math operations. It consists of circuitry that performs the math and the registers which hold the necessary information. The memory management unit is likened to the shipping department of this digital factory. It is responsible for sending data to the bus unit. Together all of the individual pieces support each other to make this digital symbiosis work as fast as possible.

To an outsider, computer nerd vernacular and all other forms of computer people esoteric may or may not be considered frightening. Probably the most confused term in microprocessor performance is Megahertz (MHz). Basically these are millions of cycles per second. This is a measurement of chip speed but is better considered the RPM of the chip (Knorr, 135). For example a 486 100 MHz processor cannot touch the speed of a Pentium running at only 60 MHz. This is because the Pentium packs more power and can do more per clock cycle. The computer bus is the data line that connects the microprocessor the rest of the computer. The width of the bus (how many bits it consists of) controls how much data can be sent to the chip per clock cycle. MIPS or millions of instructions per second is simply how many instructions the chip can perform in one second divided by 1,000,000. RISC is a commonly used term in the computing world also. It is an acronym for Reduced Instruction Set Computer. Chips that incorporate RISC technology basically rely on simplicity to enhance performance. Motorola chips use this technology. The opposite of RISC is CISC which stands for Complex Instruction Set Computer. These chips use more hardwired instructions to speed up the processing process. All Intel PC products fall into this category. Pipelining, superscalar architecture, and branch prediction logic are currently technological buzzwords in the computer community presently. These technologies can be found in newer chips. Pipelining allows the chip to seek out new data while the old data is still being worked on (Wyant and Hammerstrom, 161). Superscalar architecture allows complex instructions to be broken down into smaller ones and then processed simultaneously through separate pipelines (Wyant and Hammerstrom, 161-163). Branch prediction logic uses information about the way a program has behaved in the past to try to predict what the program will do next (Wyant and Hammerstrom, 165). Bus speed is simply the speed in MHz at which the data bus travels. This is relative to how fast the microprocessor can communicate with the rest of the computer. A register is the part of the chip that hold the information that the chip is currently manipulating. The width of the register in bits is relative to how much data the chip can process simultaneously. Using very long instruction words is simply using instructions larger than 16 bits to increase the amount of data the chip can be sent at once. A new tool being used in making chips run faster is to place a cache on the chip. This cache is for holding data that the chip is most likely to need first. Since the data is stored inside the chip the access time is lowered dramatically. In the future more and more of the computer will be integrated on the main processing unit. Line width is also a sign of the technological times. It is simply how small the smallest feature is on a chip. Basically the smaller the lines the more transistors can be squeezed onto the wafer and thus increase performance while cutting manufacturing costs.

Non-technological issues also have a major effect on the microprocessing world. One such issue is heat. This may sound trivial but a Pentium chip can and will burn the skin of a person who touches one that

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