Only once in a lifetime will a new invention come about to touch every aspect ofour lives. Such a device that changes the way we work, live, and play is aspecial one, indeed.
The Microprocessor has been around since 1971 years, but inthe last few years it has changed the American calculators to video games andcomputers (Givone 1). Many microprocessors have been manufactured for all sortsof products; some have succeeded and some have not. This paper will discuss theevolution and history of the most prominent 16 and 32 bit microprocessors in themicrocomputer and how they are similar to and different from each other. Becausemicroprocessors are a subject that most people cannot relate to and do not knowmuch about, this paragraph will introduce some of the terms that will be in-volved in the subsequent paragraphs. Throughout the paper the 16-bit and 32-bitmi- croprocessors are compared and contrasted.
The number 16 in the 16-bitmicroproces- sor refers how many registers there are or how much storage isavailable for the mi- croprocessor (Aumiaux, 3). The microprocessor has a memoryaddress such as A16, and at this address the specific commands to themicroprocessor are stored in the memory of the computer (Aumiaux, 3). So withthe 16-bit microprocessor there are 576 places to store data. With the 32-bitmicroprocessor there are twice as many places to store data making themicroprocessor faster. Another common term which is mentioned frequently in thepaper is the oscil- lator or the time at which the processors “clock” ticks.
The oscillator is the pace maker for the microprocessor which tells whatfrequency the microprocessor can proc- ess information, this value is measuredin Mega-hertz or MHz. A nanosecond is a measurement of time in a processor, or abillionth of a second. This is used to measure the time it takes for thecomputer to execute an instructions, other wise knows as a cy- cle. There aremany different types of companies of which all have their own family ofprocessors. Since the individual processors in the families were developed overa fairly long period of time, it is hard to distinguish which processors wereintroduced in order. This paper will mention the families of processors in noparticular order.
The first microprocessor that will be discussed is the familyof microprocessors called the 9900 series manufactured by Texas Instrumentsduring the mid-70s and was developed from the architecture of the 900minicomputer series (Titus, 178). There were five dif- ferent actualmicroprocessors that were designed in this family, they were the TMS9900,TMS9980A, TMS9981, TMS9985, and the TMS9940. The TMS9900 was the first of thesemicroprocessors so the next four of the microprocessors where simply variationsof the TMS9900 (Titus, 178). The 9900 series microprocessors runs with 64Kmemory and besides the fact that the 9900 is a 16-bit microprocessor, only 15 ofthe address memory circuits are in use (Titus, 179).
The 16th address is usedfor the computer to distinguish between word and data functions (Titus, 179. The9900 series microprocessors runs from 300 nanoseconds to 500 ns from 2MHz to3.3MHz and even some variations of the original microprocessor where made to goup to 4MHz (Avtar, 115). The next microprocessor that will be discussed is theLSI-11 which was pro- duced from the structural plans of the PDP-11 minicomputerfamily. There are three microprocessors in the LSI-11 family they are theLSI-11, LSI-11/2, and the much im- proved over the others is the LSI-11/32(Titus, 131). The big difference between the LSI-11 family of microprocessorsand other similar microprocessors of its kind is they have the instruction codesof a microcomputer but since the LSI-11 microprocessor originated from thePDP-11 family it is a multi-microprocessor (Avtar, 207).
The fact that theLSI-11 microprocessor is a multi-microprocessor means that many other mi-croprocessors 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 and7- 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 are 380nanoseconds, 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 arethe efficient way at which the microprocessor processes and the ability to runminicomputer software which leads to great hardware support (Avtar, 179).Although there are many strengths to the LSI- 11 family there are a couple ofweaknesses, they have limited memory and the slow- ness of speed at which theLSI-11 processes at (Avtar, 179). The next major microprocessors in themicrocomputing industry were the Z8001 and Z8002, however when themicroprocessor entered into the market the term Z8000 was used to mean either orboth of the microprocessors (Titus, 73).
So when describing the features of boththe Z8001 and the Z8002, they will be referred to as the Z8000. Themicroprocessor was designed by the Zilog Corporation and put out on the marketin 1979 (Titus, 73). The Z8000 are a lot like the many other previous micro-processors except for the obvious fact that it is faster and better, but aresimilar be- cause they depend on their registers to function properly (Titus,73). The Z8000 was improved by using 21 16-bit registers, 14 of them are usedfor general purposes opera- tions (Titus, 73).
The difference with the Z8001 andthe Z8002 is the Z8002 can only address 65K bytes of memory, which isfascinating compared to the microprocessors earlier in time but is greatlyinferior to the Z8001 which can address 8M bytes (8000K) of memory (Titus, 73).The addressing memory between the two otherwise very simi- lar microprocessorsis drastically different were as other functions of the microproces- sors seemto be quite the same. An example of this is the cycle time. The cycle time is250 nanoseconds and the average number of cycles that occur per instruction arebe- tween 10 and 14 for both microprocessors (Avtar, 25).
The nextmicroprocessor that will be discussed is the 8086. This microproces- sor is thebest in my opinion, out of all the 16-bit microprocessors. Not only because thespeeds of processing are tremendous, but because it simply paved the way to the32-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 ofthe other processors the 8086 is register oriented with fourteen 16-bitregisters, 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 inaccessing Read Only Memory. The ba- sic clock frequency for the 8086 is between4MHz and 8MHz depending on the type of 8086 microprocessor that is used (Avtar,20). Up until this point in the paper there have been common reoccurring phrasesuch as a microprocessor containing 14 16-bit registers. At this time in theevolution of microprocessors come the 32-bit register, which obviously hasdouble the capacity to hold information for the microprocessor. Because of thissimple increase of the register capacity we have a whole different type ofmicroprocessor.
Although the 16- bit and 32-bit microprocessors are quitedifferent (meaning they have more compo- nents and such), the 32-bitmicroprocessors will be described in the same terms as the 16-bitmicroprocessors were. The remainder of the paper will discuss the 32-bitmicroprocessor series. The external data bus is a term that will be referred toin the remainder of the paper is. The data bus is basically what brings datafrom 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 butare a little bit slower to access (Givone, 123).
The first 32-bit microprocessorin the microprocessor industry that will be dis- cussed is the series 32000family and was originally built for main-frame computers. In the 32000 familyall 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). Inthe 32000 family the microprocessors use only 24 of the potential 32 bitaddressing space, giving the microprocessor a 16 Mbyte address space (Mitchell,225). The 32- bit registers are set up so there are six 32-bit dedicatedregisters and then in combina- tion there are two 16-bit dedicated registers(Mitchell, 231). Each dedicated register has its own type of specificinformation that it holds for processing (Mitchell, 232).
The microprocessorsoscillator (which now comes from an external source) runs at 2.5 MHz, but due toa “divide-by-four prescaler” the clock frequency runs at 10MHz. There havebeen many new ideas put into practice to improve the 32000 series micro-processor generally and thus making it run faster and more efficient. The nextfamily of microprocessor which was fabricated for the microcomputer is theMC68020 32-bit microprocessor which is based on the MC68000 family. The othermicroprocessors that are included in this family are the MC68000, MC68008,MC68010 and the MC68012 (Avtar, 302).
Before going into the types of componentsthat this microprocessor contains, it should first be know that the making ofthe MC68020 has been the product of 60 man-years of designing including themanufac- turing of the High-density Complementary Metal Oxide Semiconductorgiving the mi- croprocessor high speed and low resistance and heat loss (Avtar,302). Because of all the work that was put into the MC68020 and its otherrelated microprocessors, it is an extremely complex microprocessor. The MC68020operates in two modes, these are the user mode(for application programs) or thesupervisor mode (the operating system and other special functions) (Mitchell,155). The user and supervisor modes all have there own specific registers tooperate their functions. The user programming has 17 32-bit address registers,and an 8-bit register (Mitchell, 155). Then the supervisor pro- gramming hasthree 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 intodifferent groups which would hold different information as usual, but this setup of registers gives the microprocessors a 20 32-bit information storingcapacity. The next family of microprocessor is Intel’s 80386 and 80486families. The 80386 and 80486 were mostly over all better then the othermicroprocessors being made by the different companies in the industry at thistime, simply because Intel is now the leading microprocessor producer intoday’s market. The 80386 was a product that evolved from Intel’s very firstmicroprocessor, the 8-bit 8080 (Mitchell, 85).
Then next came the earliermentioned 16-bit 8086. The reason why Intel did so well in the market formicroprocessors was because every microprocessor that they made was compatiblewith the previous and future (Mitchell, 85). This means that if a piece ofsoftware worked on the 8080 then it worked on the future microprocessors andvice-a- versa. Not only did Intel look forward but they looked back. The maindifference between the 80386 and the other 32-bit microprocessors is the addedfeature of a bar- rel shifter (Mitchell, 88).
The barrel shifter allowedinformation to switch places mul- tiple times in the registers within a singlecycle (Mitchell, 88). The microprocessor contains 8 general purpose 32-bitregisters, but with the barrel shifter that is increased to the equivalent of a64-bit microprocessor. For the most common 20MHz 80386 microprocessor the runtime for each cycle is 59 nanoseconds, but for a 33MHz mi- croprocessor thecycle time is reduced to 49 nanoseconds. The next 32-bit microprocessor inmarket are AT&T’s WE32100 and 32200 (Mitchell, 5).
These microprocessorsalso needed six peripheral chips in order to run, these are termed: MemoryManagement Units, floating point arithmetic, Maths Accel- eration Units, DirectMemory Access Control, and Dynamic Rand Access Memory Control (Mitchell, 5).These microprocessors apart from the microprocessors all work an important partof processing the data that comes through the microprocessor. The differencefrom this microprocessor and the others is because the WE32200 addressinformation over the 32-bit range with the help of a disk to work as a slow formof memory (Mitchell, 9). The WE32200 microprocessor runs at a frequency of 24MHz(Mitchell, 9). The 16-bit and 32-bit microprocessors are a mere page in thegreat book of processor history.
There will be many new and extremely differentprocessors in the near future. A tremendous amount of time and money have beenput into the making and improving of the microprocessor. The improving andinvestment of billions of dollars are continually going toward the cause ofelaborating the microprocessors. The evolution of the microprocessor willcontinue to evolve for the better until the time when a much faster and moreefficient electronic device is invented. This is turn will create a whole newand powerful generation of computers. Hopefully this paper has given the readersome insight into the world of microprocessor and how much work has been putinto the manufacturing of the microprocessor over the years.
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