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    The Evolution Of The Microprocessor (2131 words) Essay

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    The Evolution of the Microprocessor

    Only once in a lifetime will a new invention come about to touch every aspect of our lives. Such a device that changes the way we work, live, and play is special indeed. The microprocessor has been around since 1971, but in the last few years, it has changed American calculators to video games and computers (Givone 1). Many microprocessors have been manufactured for all sorts of products; some have succeeded, and some have not.

    This paper will discuss the evolution and history of the most prominent 16- and 32-bit microprocessors in the microcomputer and how they are similar to and different from each other. Because microprocessors are a subject that most people cannot relate to and do not know much about, this paragraph will introduce some of the terms that will be involved in the subsequent paragraphs. Throughout the paper, the 16-bit and 32-bit microprocessors are compared and contrasted. The number 16 in the 16-bit microprocessor refers to how many registers there are or how much storage is available for the microprocessor (Aumiaux 3). The microprocessor has a memory address such as A16, and at this address, the specific commands to the microprocessor are stored in the memory of the computer (Aumiaux 3).

    So with the 16-bit microprocessor, there are 576 places to store data. With the 32-bit microprocessor, there are twice as many places to store data, making the microprocessor faster. Another common term mentioned frequently in the paper is the oscillator or the time at which the processor’s “clock” ticks. The oscillator is the pacemaker for the microprocessor, which tells what frequency the microprocessor can process information; this value is measured in megahertz or MHz.

    A nanosecond is a measurement of time in a processor, or a billionth of a second. This is used to measure the time it takes for the computer to execute instructions, otherwise known as a cycle. There are many different types of companies, all of which have their own family of processors. Since the individual processors in the families were developed over a fairly long period of time, it is hard to distinguish which processors were introduced in order. This paper will mention the families of processors in no particular order. The first microprocessor that will be discussed is the family of microprocessors called the 9900 series, manufactured by Texas Instruments during the mid-70s and developed from the architecture of the 900 minicomputer series (Titus 178).

    There were five different actual microprocessors that were designed in this family: the TMS9900, TMS9980A, TMS9981, TMS9985, and the TMS9940. The TMS9900 was the first of these microprocessors, so the next four of the microprocessors were simply variations of the TMS9900 (Titus 178). The 9900 series microprocessors run with 64K memory, and besides the fact that the 9900 is a 16-bit microprocessor, only 15 of the address memory circuits are in use (Titus 179). The 16th address is used for the computer to distinguish between word and data functions (Titus 179). The 9900 series microprocessors run from 300 nanoseconds to 500 ns from 2MHz to 3.3MHz, and even some variations of the original microprocessor were made to go up to 4MHz (Avtar 115).

    The next microprocessor that will be discussed is the LSI-11, which was produced from the structural plans of the PDP-11 minicomputer family. There are three microprocessors in the LSI-11 family: they are the LSI-11, LSI-11/2, and the much-improved LSI-11/32 (Titus, 131). The big difference between the LSI-11 family of microprocessors and other similar microprocessors of its kind is that they have the instruction codes of a microcomputer, but since the LSI-11 microprocessor originated from the PDP-11 family, it is a multi-microprocessor (Avtar, 207). The fact that the LSI-11 microprocessor is a multi-microprocessor means that many other microprocessors are used in conjunction with the LSI-11 to function properly (Avtar, 207). The LSI-11 microprocessor has a direct processing speed of 16-bit word and 7-bit data; however, the improved LSI-11/22 can directly process 64-bit data (Titus, 131).

    The average time that the LSI-11 and LSI-11/2 process at is 380 nanoseconds, while the LSI-11/23 is clocked at 300 nanoseconds (Titus, 132). There are some great strengths that lie in the LSI-11 family, some of which are the efficient way at which the microprocessor processes and the ability to run minicomputer software, which leads to great hardware support (Avtar, 179). Although there are many strengths to the LSI-11 family, there are a couple of weaknesses: they have limited memory and the slowness of speed at which the LSI-11 processes (Avtar, 179).

    The next major microprocessors in the microcomputing industry were the Z8001 and Z8002. However, when the microprocessor entered into the market, the term Z8000 was used to mean either or both of the microprocessors (Titus, 73). So when describing the features of both the Z8001 and the Z8002, they will be referred to as the Z8000. The microprocessor was designed by the Zilog Corporation and put out on the market in 1979 (Titus, 73).

    The Z8000 is a lot like the many other previous microprocessors, except for the obvious fact that it is faster and better, but are similar because they depend on their registers to function properly (Titus, 73). The Z8000 was improved by using 21 16-bit registers, 14 of them are used for general purpose operations (Titus, 73). The difference with the Z8001 and the Z8002 is that the Z8002 can only address 65K bytes of memory, which is fascinating compared to the microprocessors earlier in time but is greatly inferior to the Z8001, which can address 8M bytes (8000K) of memory (Titus, 73). The addressing memory between the two otherwise very similar microprocessors is drastically different, whereas other functions of the microprocessors seem to be quite the same. An example of this is the cycle time. The cycle time is 250 nanoseconds, and the average number of cycles that occur per instruction is between 10 and 14 for both microprocessors (Avtar, 25).

    The next microprocessor that will be discussed is the 8086. This microprocessor is the best, in my opinion, out of all the 16-bit microprocessors. Not only because the processing speeds are tremendous, but because it paved the way to the 32-bit microprocessors using various techniques that will be discussed later. The 8086 was the second Intel microprocessor, being preceded by the 8080 (Avtar, 19). The 8086 was introduced in early 1978 by Intel (Avtar, 19). Like so many other processors, the 8086 is register-oriented with fourteen 16-bit registers, eight of which are used for general processing purposes (Avtar, 19).

    The 8086 can directly address 1MB (1,048,576 bytes), which is used only in accessing Read-Only Memory. The basic clock frequency for the 8086 is between 4MHz and 8MHz, depending on the type of 8086 microprocessor used (Avtar, 20). Up until this point in the paper, there have been common reoccurring phrases such as a microprocessor containing 14 16-bit registers. At this point in the evolution of microprocessors, the 32-bit register comes, which obviously has double the capacity to hold information for the microprocessor.

    Because of this simple increase in register capacity, we have a whole different type of microprocessor. Although 16-bit and 32-bit microprocessors are quite different, meaning they have more components and such, the 32-bit microprocessors will be described in the same terms as the 16-bit microprocessors. The remainder of the paper will discuss the 32-bit microprocessor series. The external data bus is a term that will be referred to in the remainder of the paper.

    The data bus is basically what brings data from the memory to the processor and from the processor to the memory (Givone, 123). The data bus is similar to the registers located on the microprocessor but is a little bit slower to access (Givone, 123). The first 32-bit microprocessor in the microprocessor industry that will be discussed is the series 32000 family and was originally built for mainframe computers. In the 32000 family, all of the different microprocessors have the same 32-bit internal structure, but may have external bus values such as 8, 16, or 32 bits (Mitchell, 225). In the 32000 family, the microprocessors use only 24 of the potential 32-bit addressing space, giving the microprocessor a 16Mbyte address space (Mitchell, 225).

    The 32-bit registers are set up so there are six 32-bit dedicated registers and then, in combination, there are two 16-bit dedicated registers (Mitchell, 231). Each dedicated register has its specific information that it holds for processing (Mitchell, 232). The microprocessor’s oscillator (which now comes from an external source) runs at 2.5MHz, but due to a “divide-by-four prescaler”, the clock frequency runs at 10MHz. Many new ideas have been put into practice to improve the 32000 series microprocessor generally and thus making it run faster and more efficiently. The next family of microprocessor, which was fabricated for the microcomputer, is the MC68020 32-bit microprocessor, which is based on the MC68000 family.

    The other microprocessors that are included in this family are the MC68000, MC68008, MC68010, and the MC68012 (Avtar, 302). Before going into the types of components that this microprocessor contains, it should first be known that the making of the MC68020 has been the product of 60 man-years of designing, including the manufacturing of the High-density Complementary Metal Oxide Semiconductor, giving the microprocessor high speed and low resistance and heat loss (Avtar, 302). Because of all the work that was put into the MC68020 and its other related microprocessors, it is an extremely complex microprocessor. The MC68020 operates in two modes: the user mode (for application programs) or the supervisor mode (the operating system and other special functions) (Mitchell, 155). The user and supervisor modes all have their own specific registers to operate their functions.

    The user programming has 17 32-bit address registers and an 8-bit register (Mitchell, 155). Then the supervisor programming has three 32-bit, an 8-bit, and two 3-bit registers for small miscellaneous functions (Mitchell, 155). All of these registers within the two modes are split up into different groups, which would hold different information as usual, but this setup of registers gives the microprocessors a 20 32-bit information storing capacity. The next family of microprocessors is Intel’s 80386 and 80486 families.

    The 80386 and 80486 were mostly overall better than the other microprocessors being made by the different companies in the industry at this time, simply because Intel is now the leading microprocessor producer in today’s market. The 80386 was a product that evolved from Intel’s very first microprocessor, the 8-bit 8080 (Mitchell, 85). Then next came the earlier mentioned 16-bit 8086. The reason why Intel did so well in the market for microprocessors was that every microprocessor that they made was compatible with the previous and future (Mitchell, 85). This means that if a piece of software worked on the 8080, then it worked on the future microprocessors and vice versa.

    Not only did Intel look forward, but they also looked back. The main difference between the 80386 and the other 32-bit microprocessors is the added feature of a barrel shifter (Mitchell, 88). The barrel shifter allowed information to switch places multiple times in the registers within a single cycle (Mitchell, 88). The microprocessor contains 8 general-purpose 32-bit registers, but with the barrel shifter, that is increased to the equivalent of a 64-bit microprocessor. For the most common 20MHz 80386 microprocessor, the run time for each cycle is 59 nanoseconds, but for a 33MHz microprocessor, the cycle time is reduced to 49 nanoseconds.

    The next 32-bit microprocessors in the market are AT&T’s WE32100 and 32200 (Mitchell, 5). These microprocessors also require six peripheral chips to run, which are called Memory Management Units, floating point arithmetic, Maths Acceleration Units, Direct Memory Access Control, and Dynamic Random Access Memory Control (Mitchell, 5). These microprocessors, apart from the microprocessors themselves, work as an important part of processing the data that comes through the microprocessor. The difference from this microprocessor and the others is that the WE32200 addresses information over the 32-bit range with the help of a disk to work as a slow form of memory (Mitchell, 9). The WE32200 microprocessor runs at a frequency of 24MHz (Mitchell, 9). The 16-bit and 32-bit microprocessors are mere pages in the great book of processor history.

    There will be many new and extremely different processors in the near future. A tremendous amount of time and money has been put into the making and improving of the microprocessor. The improvement and investment of billions of dollars are continually going toward the cause of elaborating the microprocessors. The evolution of the microprocessor will continue to evolve for the better until the time when a much faster and more efficient electronic device is invented. This in turn will create a whole new and powerful generation of computers.

    Hopefully, this paper has given the reader some insight into the world of microprocessors and how much work has been put into the manufacturing of the microprocessor over the years.


    1. Mitchell, H. J. 32-bit Microprocessors. Boston: CRC Press, 1986, 1991.
    2. Titus, Christopher A. 16-Bit Microprocessors. Indiana: Howard W. Sams & Co., Inc., 1981.
    3. Aumiaux, M. Microprocessor Systems. New York: John Wiley & Sons, 1982.
    4. Givone, Donald D.; Rosser, Robert P. Microprocessors/Microcomputers. New York: McGraw-Hill Book Company, 1980.
    5. Avtar, Singh. 16-Bit and 32-Bit Microprocessors: Architecture, Software, and Interfacing Techniques. New Jersey: Englewood Cliffs, 1991.

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