How to Choose a Microprocessor Lou Frenzel All personal and hobby computers are With this wide variety, is it any wonder Heath Company microprocessor based. That is, they use a that it is a difficult choice? Yet with all of Benton Harbor MI 49022 single processor integrated circuit chip. these available devices, the choice narrows One of the most important decisions you down rather quickly when several important will ever make in purchasing a personal factors are considered. What makes things computer is choosing the type of micro- even more confusing is the fact that many of processor. The semiconductor manufacturers the above microprocessors will undergo have provided computer designers with a changes and improvements. Semiconductor wide range of microprocessing units having manufacturers will also develop and intro- varying degrees of power and sophistication. duce even newer improved microprocessors. As a result, there are at least a half dozen The whole microprocessor business is a different processors available in hobby dynamic one. Changes occur almost daily. computers. This wide variety of products The biggest dilemma is not so much the makes your choice somewhat flexible, or changes themselves but the rapidity with at least it seems that way. In reality, having which they occur. Today you may make a so many processor styles to choose from, decision to use a particular microprocessor your decision becomes much tougher. If only to find that six months later the choice you are a beginner, it may be particularly is apparently incorrect because a newer, difficult to make an intelligent choice. The better, improved device has become avail- purpose of this article is to provide you with able. There is no complete solution to this some guidelines in making this important problem. The rapid changes in this field decision. The emphasis is on how to choose will continue to occur. For that reason, the best microprocessor for you when pur- you must make a choice and stick with it. chasing a personal computer. You must attempt to select a device that has the greatest longevity potential as well What's Available as one that meets the criterion for perform- Below is a list of all of the available ance in your application. You must not let microprocessor architectures and their pri- the rapidly changing technology paralyze mary manufacturers. your decision making process. It is best to choose among the presently available devices Intel 8080, 8085, 8048, 8086 and take your chances with the future. To Motorola 6800 obtain the most value from your personal MOS Technology 6502 computing system, you must select a micro- Zilog Z-80, Z8000 processor that meets your immediate needs Signetics 2650 but offers future potential as well. RCA 1802 Fairchild F8, 9440 Selection Criteria MOSTEK 3870 ntersil 6100 There are many factors that go into the Texas Instruments 9900 process of selecting a microprocessor. You National Semiconductor SC/M P, PACE, 8900 should consider all of these factors even DEC LSI-11 though some of them affect you only in- Data General microNova directly. You should also be influenced by General Instrument 1600 the factors that ordinarily would interest 124 July 1978 © BYTE Publications Inc only the designer. Below are listed some of the key elements in choosing a microprocessor. Cost Cost is always a major consideration in choosing a microprocessor. However, of all the factors involved, this is one that the user should be least concerned about. Cost is primarily the concern of the computer manufacturer. Most microprocessor inte- grated circuits are in the same price range; and the cost of the microprocessor itself is only a fraction of the overall cost of the computer system. The cost of memory and peripherals is far more than the cost of the processor. Thus for purposes of our dis- cussion here, cost is irrelevant. Speed One of the factors considered in the evaluation or comparison of computers is processing speed . This is the rate at which From the machine and assembly instructions are executed . While speed is language programmer's point of view, primarily a function of the clock frequency the Signetics 2650 processor shown here and the upper frequency limit of the micro- is often considered to be a superior processor itself, it is also affected by the machine. But it has never become popular memory speed and the architecture of the in the personal computing field, most processor. Most modern microprocessors are likely because it entered the 8 bit market- not known for their processing speed. After place later than the major contenders. all, most microprocessors are metal oxide This photograph was supplied by Sig- semiconductor (MOS) circuits which are netics. inherently slower than bipolar (TTL) cir- cuits. Over the years great improvements have been made in the speed of MOS cir- cuits. The slow "P channel " circuits have been gradually replaced by smaller and faster " N channel " circuits. Continuing developments in the N channel process promise even further improvements in speed. Speeds approaching bipolar levels are achievable . If processing speed is the most important criterion, then bipolar circuits should be selected over MOS microproc- essors. Speed is of little or no consideration in choosing a microprocessor - based personal computer. Most MOS microprocessors used in personal computers execute an instruction within several microseconds which is fast The Digital Group leaves out no major microprocessor choice. While enough for most applications. their emphasis is on the Z-80 processor, they cover all bases with options While processing speeds can vary as much for 8080, 6800, 6502 and Z-80 processor boards. This photo, supplied by as four to one among MOS microprocessors, Digital Group, shows a board which features the 8080 processor. the difference is almost unnoticeable. For July 1978 0 BYTE Publications Inc 125 Circle 43 on inquiry card. example, most hobbyists use the BASIC language. The speed of the microprocessor will definitely determine the length of time that it takes to execute a program. However, with an interpretive language such as BASIC, an order of magnitude difference in execu- tion speeds is frequently almost unnotice- able to the user. While it may take 200 ps to execute a program on one computer and I 20 /is on another, the user is often totally 1 incapable of recognizing the difference. The real value of speed comes when your application requires it. If your applications 000 involve lengthy, complex mathematical operations or highly complex real time functions, speed may be an important con- 00 * enm.ze < .ss7 sideration. Otherwise, speed is one factor us pp g which you could practically ignore in the ' IN KIT FORM and Handling 1 selection of a personal computer. Few per- • 80 CHARACTERS/LINE • 75-19,200 BAUD 1 sonal computer manufacturers know how to • 24 LINES/SCREEN • FULL & HALF DUPLEX specify it, let alone mention it. • ADDRESSABLE CURSUR • ODD/EVEN/NO PARITY n • 9, 10, or 11 BIT WORDS • RS232 INTERFACE OR 20 ma CURRENT LOOP Computing Power GET COMPLETE DETAILS WITH A DIRECT CALL: Computing power is a rather nebulous 214 2582414 TWX 910.860.5761 TELEX 73-0022 800 527-3248 ' designation that refers to the power of the instruction set and architecture of the com- jv^ capital puter. Computing power also effectively I equipment brokers involves speed as discussed above. Yet 930 N. BELTLINE IRVING, TEXAS 75061 computing power is far more important ----mss ------- than raw speed in determining the capa- bilities of a microprocessor. It is difficult to provide any specific guidelines for determining whether one microprocessor is more powerful than KIMSI another. However, as a general guideline there are several factors to look for in determining which microprocessor has the greatest power. These factors are: number of instructions in the instruction set, number of working registers, and number and type of addressing modes. Those microprocessors with the greatest numbers of instructions, registers, and addressing modes are essentially the more powerful microprocessors. They The KIM to S-100 bus can accomplish more complex operations in less time than other microcomputers with Interface/Motherboard lesser characteristics. • Combines the power of the 6502 with the flexibility of It is the wide variation in architectures the S-100 bus which makes the choice of a microprocessor • Attaches to any unmodified KIM • Complete interface logic and fully buffered motherboard interesting. In some cases, a superior in- in one unit struction set, more flexible register organiza- • On-board regulation of power for KIM tion and more addressing modes can offset • Eight slots of S-100 compatibility for additional RAM, Video and I/O boards, PROM Programmers, Speech the superior computing speed of another processors... microprocessor with a simpler architecture. • Includes all parts, sockets for ICs, one 100 pin connector, There are never any clear cut answers to and full Assembly/Operating documentation the question of which microprocessor is • Kit $125, Assembled $165 the most powerful since usually the answer • All units shipped from stock lies in a specific application. When a partic- ular application can be defined, the choice FORETHOUGHT PRODUCTS of microprocessor can be optimized. How- P.O. Box 386-F ever, when choosing a microprocessor-based Coburg, OR 97401 ui^J general purpose computer which must be 126 July 1978 0 BYTE Publications Inc Circle 140 on inquiry card. Circle 265 on inquiry card. MPI useable in a wide range of applications, the QUALITY CONTROL TEST speed and computing power consideration f'.El'BiO44P0 TEST 26s6 BHtJD PS232 SERIAL PORT becomes fuzzy at best. EtE,: FD TET 3013 E0UD CURP,ENT LOOP i06 _INE ?E'.? ?606 EwUL' P52'2 Rill FORT Second Sources BUFF EF7 WF'i- F' AF'OUND Another way to assess the value of a i ' l 4 _'= "t 45..,F_+t 1 34%rbyN ._r IF.F e.c 1E_r r-w T-TE.t5I1 f--at.