197811 Byte Magazine Vol 03 11 OSCAR amateur radio satellites

NOVEMBER 1978 = VOLUME 3, Number 11 $2 00 in USA VIE @ the small systems journal Someday all terminals will be smart....... @ 128 Functions—software controlled @ 82 x 16 or 92 x 22 format—plus graphics @ 7x 12 matrix, upper/lower case letters @ Printer output port 50 to 38,400 baud—selectable @ “CHERRY” keyboard CT-82 Intelligent Terminal, assembled and tested. $795.00 ppd in Cont. U.S. SOUTHWEST TECHNICAL PROD ‘S CORPORATION 219 W. RHAPSODY Yt SAN ANTONIO, TEXAS 78216 Circle 350 on inquiry card. Paraliel 1/0 Port #1 Parallel 1/0 Port #2 Parallel 1/0 Port #3 8K ROM 1K RAM RS-232 or Current Loop 1/0 Port #4 Programmable Baud Rate UART with Interval Timers. 4,MHz Z-80A Completely Buttered Bus Intertace Standard Bus tor System Expandabiiity The single card computer with the features that help you in real life COMPLETE COMPUTER In this advanced card you get a pro- fessional quality computer that meets today’s engineering needs. And it’s one that’s complete. It lets you be up and running fast. All you need is a power supply and your ROM software. The computer itself is super. Fast 4 MHz operation. Capacity for 8K bytes of ROM (uses 2716 PROMs which can be programmed by our new 32K BYTE- SAVER® PROM card). There’s also 1K of on-board static RAM. Further, you get straightforward interfacing through an RS-232 serial interface with ultra-fast speed of up to 76,800 baud — software programmable. Other features include 24 bits of bi- directional parallel 1/O and five on- board programmable timers. Add to that vectored interrupts. Circle 80 on inquiry card. ENORMOUS EXPANDABILITY Besides all these features the Cro- memco single card computer gives you enormous expandability if you ever need it, And it’s easy to expand. First, you can expand with the new Cromemco 32K BYTESAVER PROM card mentioned above. Then there’s Cromemco’s broad line of $100-bus-compatible memory and 1/O interface cards. Cards with fea- tures such as relay interface, analog interface, graphics interface, opto- isolator input, and A/D and D/A con- version. RAM and ROM cards, too. Card Cage Cromemco 7S 626 oF pee € On 7 ee Specialists in computers and peripherals 32K BYTESAVER PROM card EASY TO USE nal Another convenience that makes the Model SCC computer easy to use is our Z-80 monitor and 3K Control BASIC (in two ROMs). With this optional software you're ready to go. The monitor gives you 12 commands. The BASIC, with 36 — commands/functions, will directly ac- cess 1/O ports and memory locations — and call machine language subroutines. Finally, to simplify things to the ulti- mate, we even have convenient card cages. Rugged card cages. They hold cards firmly. No jiggling out of sockets. AVAILABLE NOW/LOW PRICE The Cromemco Model SCC is avail- able now at a low price of only $450 factory assembled ($395 kit). So act today. Get this high-capability computer working for you right away. 280 BERNARDO AVE., MOUNTAIN VIEW, CA 94040 (415) 964-7400 BYTE November 1978 1 SEE YOUR LOCAL CROMEMCO DEALER eee 22a oman ee = == oe Eom. a ae = se~ 2S peas opis Scores = = aS —— ss ag ko aap ee = SS =— en = a = = =. ae eS ee fore ee San lo secrete See ome = - ee cuyesee ae ee pee pec * eee as Rc aes == al coal — = poe sans =~ al es Sener — =a =" eee a oem SSeS ae lanai Rees =~ i3e-~ = pan cS mer [aoe a =e Soe Fee none Bier ee, ae = ps Precsn seas, ‘maar eae Samia =e aims Toman. sa + pecime seer ae ESE Sire coer Ree Ser. ‘ee =< on SAEZ aroun = =a” |e = a a Seer sax ‘saa Sees Sa = See = Benen * pemteen aie = Poe boi SS vee ee ig ee ae i ieee ae a i We --6, “eipl ot tro an te old! Specialists in computers and peripherals 2 BYTE November 1978 280 BERNARDO AVE., MOUNTAIN VIEW, CA 94040 © (415) 964-7400 Circle 80 on inquiry card. In the Queue BUTE November 1978 Volume 3 Number 11 AN EXCHANGE EVALUATOR FOR COMPUTER CHESS Software Chess—the Spracklens THE SKY‘S THE LIMIT: Ham Radio for Intercomputer Communication Personal Computing Networks—Kasser I'VE GOT YOU IN MY SCANNER! Applications—Ciarcia DEFINING A LANGUAGE: PL/B Languages Forum—Wilson A CLASSROOM DEMONSTRATION Control Systems—Hill A MULTIUSER DATA NETWORK: Communicating Over VHF Radio Networking—Bruninga A CASSETTE INTERFACE SWITCHING BOX FOR THE TRS-80 Hardware—Anderton CREATING A CHESS PLAYER, Part 2: Chess 0.5 Computer Chess Software—Frey-Atkin A “TINY” PASCAL COMPILER, Part 3: P-Code to 8080 Conversion Pascal~Chung-Yuen FUNCTIONAL APPROXIMATIONS Numbers—Ruckdeschel DISTRIBUTED NETWORK Networking—Horton COMPUTER ASSISTED INSTRUCTION ON A MICROCOMPUTER Applications—Gerhold HOBBYIST COMPUTERIZED BULLETIN BOARD Personal Computing Networks—Christensen-Suess HEATH MICROPROCESSOR TRAINING SYSTEM Product Review—Hubin In This BYTE On the Virtues of Writing Editors Letters Programming Quickie: Checkbook Balancer Machine Language Puzzler: TIMOUT Event Queue Book Reviews Puzzle: Hextext Technical Forum: Transmission of Digital Data BYTE's Bits BYTE’s Bugs Clubs, Newsletters What's New? Unclassified Ads BOMB NEY é Reader Service fut BYTE is published monthly by BYTE Publications Inc, 70 Main St, Peterborough NH 03468. Address all mail except sub- ‘address: phone (603) 924-7217. Address all editorial correspondence to the editor at the above address. Unacceptable manuscripts will be returned if eccompanied by sufficient first class postage. Not retpontible for lost manu- scripts or photos. Opinions expressed by the authors are not necessarily those of BYTE. Address all subscriptions, changa of ‘address, Form 3579, and fulfillment to BYTE Subscriptions, PO Box 690, NJ 08836. Second class Postape paid at Peterborough NH C468 and at sddtional mailing officer USPS Publication No. 102410, Canadian vecond class registration No. 9321. Subscriptions are $15 for one year, $27 for two years, and $39 for three yeors in the USA and its Possessions. In Cenade and Mexico, $17.50 for one yaer, $32 for two yeers, and $46.50 for three years. $25 for 2 one your subscription by mai Air to areas at ‘rates available upon request. $25 for a one: ‘year subscription by sir delivery to Europe. Single copy price is $2.00 in the USA and its possessions, $2.40 in Caneda and ‘Mexico, $3.50 in Europe, and $4.00 elsewhere. Foreign subscriptions and sales Printed in United States of America. Each separate contribution to this istue and the issue es a collective work copyright 1978 by BYTE Publication Inc. All rights reserved. Subscription WATS Line: (800) 258-5485 shauid be remicind in United Stes funds, PUBLISHERS Helmers Je VICE-PRESIDENT, PRODUCTION Judith Havey PRODUCTION MANAGER Karen Gregory ADVERTISING DIRECTOR John Hayes CIRCULATION MANAGER 72 A Hanson ASSISTANT ADVERTISING DIRECTOR Patricia Clark ADVERTISING PRODUCTION COORDINATOR ‘Thomas Harvey [ADVERTISING ASSISTANTS, Noreen Bar 10 Callan ‘COMPTROLLER Kevin Maguire ASSISTANT TO COMPTROLLER Mary Steiner ASSISTANT TO PUBLISHERS. Ruth M Walsh EDITORIAL ASSISTANT Gale Britton CIRCULATION ASSISTANTS, Christine Dixon ADVERTISING SALES REPRESENTATIVES, Hajar Associates toe 17 Durant St West Roxbury MA 02132 (617) 325-5380 100 W Chicago Av About the Cover This month's cover by artist Ken Lodding emphasizes the personal com- puting potential of the OSCAR amateur radio satellites described in Joe Kasser’s article on page 48. When Ken isn’t doing technology-related art work, he helps design and implement experimental systems for Digital Equipment Corp in Merrimack NH. In This BUTE One of the basic building blocks of any computer chess playing program is the exchange evaluator. Authors Dan and Kathe Spracklen describe the exchange evaluator used in their Sargon program in An Exchange Evaluator for Computer Chess. page 16 Taylor series expansions are not necessarily the best polynomial ap- proximations for many functions. Fred R Ruckdeschel describes several minimax and = rational polynomial approximations for some common functions in Functional Approxi- mations. A method for creating poly- nomial approximations for micro- computers using mathematical tables and large system statistical routines is also discussed. page 34 One method of connecting com- puters into a communications net- work is by VHF radio stations. To ease some of the physical difficulties encountered with this arrangement, a satellite can be introduced into the system, and then, as Joe Kasser says, The Sky’s the Limit for personal computer users. page 48 One theme of this issue is VHF communication among computers to produce a network. There are other types of networks which are available to computer users. One of these uses a Distributed Network, which is de- scribed by Glen R Horton. page 62 Ciarcia’s Circuit Cellar turns to 4 November 1978.© BYTE Publications Inc {——~) sumeer -001, TO PROCESSORS E ALLOCATE | Jrooness oer Ae: Ct. 100 si coe SHARED SLOT AND ATTACHED. MEMORY OR INTERFACE page 62 melodrama this month as Steve and Lloyd are confronted by a mysteri- ous stranger. All ends happily, how- ever, with the aid of a computer controlled stepper motor driven infra- red and visible light scanner, Read I’ve Got You in My Scanner! page 76 One of the more fascinating uses of a computer, teaching courses, is frequently known as computer assisted instruction. George A Gerhold de- scribes one group of people that is actively involved in implementing Computer Assisted Instruction on a Microcomputer. page 90 As part of the never ending struggle for truth, beauty and the ultimate in high level languages, David Wilson provides readers with a Languages Forum proposal, Defining a Language: PL/B, a combination of some of the features of a high level language like BASIC with access to assembly lan- guage details when necessary. page 100 Controlling a physical system is a natural for the microprocessor: parameters can often be changed in a matter of seconds in software without any mechanical changes to the system. A simple airflow control system is described in Garnet L Hill’s article, A Classroom Demon- stration: Controlling a System with a Microcomputer. page 112 The VHF communication network already in existence provides a readily available communication network for the computer experimenter. R E Brun- inga describes one system which is up and running in his article A Multiuser Data Network. page 120 A home computer system can be used for communication among many people. This month Ward Christensen and Randy Suess describe their imple- mentation of a Hobbyist Computer- ized Bulletin Board. page 150 For people who are just being intro- duced to the world of micropro- cessors, the first steps can seem con- fusing. For a description of one device which can aid the introduction read WN Hubin’s review of the Heath Microprocessor Training System. page 158 Craig Anderton’s simple circuit described in A Cassette Interface Switching Box for the TRS-80 shows you how to operate the cassette re- corder manually and monitor tapes while they are being read in without having to unplug any cables. page 160 This month we continue the series Creating a Chess Player by Peter W Frey and Larry R Atkin with the first half of Chess 0.5, a program written in Pascal by Larry Atkin, who is co- author with David Slate of the world championship computer chess pro- gram, Chess 4.6. page 162 In this issue, Kin-Man Chung and Herbert Yuen conclude their series of articles on A “Tiny” Pascal Compiler with a discussion of a p-code (pseudo- code) to 8080 code conversion pro- gram and the needed runtime routines. Page 182 DEAR BOSS JUST THOUGHT I'D LET YOU KNOW THAT I'M BACK FROM THE COMPUTER SHOW. THE TERMINAL WE WANT 1S THE IQI20 __ FROM SOROC (SEE ___ SNAP SHOT). THIS UNIT 1S —™ NOT ONLY SMART LOOKING, BUT HAS ALL THE FEATURES WE NEED IN THE BASIC PRICE. _ FOR EXAMPLE: THE IQ 120 INCLUDES NUMERIC KEYPADS AND PROTECT FIELDS AS STANDARD. ‘I LOOKED AT THE OTHER TERMINALS AS You SUGGESTED, BUT FOUND THEM TO BE EITHER PAPER - TIGERS”, oR TOO “pumB” FoR OUR CONSIDERATION. ANYWAY, YOU ASKED ME TO DECIDE AND AT $995 * ror THE TQ 120, IT WAS THE EASIEST ASSIGNMENT I’VE HAD. REGARDS Ci Bag 'S® EREEDOM a1 aE: eae DOM.AVE, ANAHEIM, CA. 9280) 6 Ecitoria By Carl Helmers Editors. This is a word of multiple de- finitions. One definition is implicit in the job description of myself and my associates at BYTE. Another definition is that applied to a class of utility programs which every BYTE reader’s computer system has in some form or another. It is this latter definition which provides the subject for this editorial. What is often ignored is the fact that editor programs make an excellent form of software project, less complex than an interpreter or a compiler, but of sufficient magnitude to be interesting and educational. The problems and characteristics of editors are analogous to those of compilers and interpreters, especially when viewed as tools of software development. Just as compilers beget better compilers, editors can be used to edit better editors. On the Virtues of Writing Editors November 1978 © BYTE Publications Inc Software projects are some of the most exciting avocational applications of personal computers, applications which emphasize computing as an art form and means of expression of personal tastes. This editorial on the philosophy of software projects in general and text editing in particular was inspired by recent completion of a text editor begun as a spare time project in March of this year. Five months and many evening and weekend hours later it is now mid August and the editor program is working sufficiently well to serve as the primary monitor program and software tool of my homebrew computer system. Why Write an Editor Program? There are alternatives to do-it-yourself. In the usual case of purchasing a commercial system from a computer store, an editor program is built into the systems software of the computer. The present day tech- nology of self-contained desktop computers with read only memory systems software (BASIC interpreters) invariably includes primitive line oriented editors built into the computer. On computers which have assemblers plus high level language facilities like Pascal, C, FORTRAN or COBOL or brand X, one or more forms of more useful text editing pro- grams may be available in order to prepare source language files. This is the configu- ration found in the typical $3000+ personal microcomputer or $10,000+ commerical minicomputer system. Even hardware homebrewers do not necessarily have to start completely from scratch with editor software. Often a micro- processor chosen for a homebrew system has a software package which can be purchased from one of a number of software vendors. And in the newer processor designs like the Motorola 6809, complete dynamic relocat- ability of code allows systems software to be sold in address space position independent read only memory chip sets which home- brewers can expect to have access to over the next few years. But to do-it-yourself is one of the princi- ple reasons why people get involved in intricate avocational pursuits. Why does the amateur wine maker inject yeast into juice and wait for the results when Napa Valley and its industries exist? Why does the ama- teur pilot learn to fly when professional transportation options are available from the largest airline to the smallest air taxi service? Why make your own astronomical telescope when there exists such a perfec- tion as Questar? And similarly in computers, why make your own text editor, compiler or computer when so many options exist in the marketplace? On a practical or short term basis there is no visible advantage to engaging in such pursuits. But on a long- term scale of personal development, ac- tively applying one’s mind and energy is always rewarding. What Was Needed? With this spirit .nd a secondary purpose of improved systems software in mind, I proceeded to think about writing an editor program. What is required in a personal computer system to engage in a project of this complexity? The requirements are essentially identical to the requirements for programming any arbitrary application of the personal computer, from electronic music systems to sophisticated information storage and retrieval systems: tools. Soft- ware tools are needed in order to create more software, and software tools pre- suppose a certain hardware basis. The hardware components needed for a useful system are available right now from a Continued on page 68 Specifications: S-100 compatible. MFM encoding, 35 tracks with ten 512-byte sectors per track. 179,200 bytes or double density SA-400 and North Star BASIC, DOS, and Monitor included. For further information, write for full color catalog or contact your local computer store. New from North Star Double Density Performance at Single Density Prices The new HORIZON computer and Micro Disk System now record in dou- ble density! That means each new Shugart SA-400 minifloppy disk drive accesses 180K bytes of on-line infor- mation. All double density HORIZON computers and Micro Disk Systems have a redesigned controller which allows the use of quadruple capacity disk drives as they become available in early 1979. A three-drive North Star System with quadruple capacity disk drives will access over a megabyte of on-line information. But, best of all there’s no price increase for double density models. North Star BASIC and DOS have been upgraded to accommodate the in- creased capacity and yet run existing programs with little or no change. The new disk system also supports single density, so existing single density disk- ettes can still be used. Single density SA-400 drives previously purchased with North Star systems can also be used. Pricing HORIZON with one double density SA-400 minifloppy (180K bytes), 16K RAM, Z80A processor and serial 1/O port: $1599 kit, $1899 assembled. MICRO DISK SYSTEM with one double density SA-400 minifloppy, controller board and power regulation: $699 kit, $799 assembled. (Cabinet and power supply $39 extra each.) NoatH Star %& Coweuters 2547 Ninth Street Berkeley, California 94710 (415) 549-0858 Circle 285 on inquiry card. BYTE November 1978 7 Sol. The small computer that won't fence A lot of semantic nonsense is being tossed around by some of the makers of so-called “personal” computers. To hear them tell it, an investment of a few hundred dollars will give you a computer to run your small business, do a great amount of financial planning, analyze a host of data in the engineering or scientific lab and when day is done play games by the hour. Well, the games part is true. The rest of the claims should be taken with a grain of salt. All of the personal computers will help you learn about computers and how they work in general and the kinds of things they can do for you. Only a few have the capacity to grow and handle meaningful work in a very real sense. And they don't come for peanuts. Remember, there's no free lunch. So before you buy any personal computer, consider Sol* the small computer. Consider it because it costs more at the start so in the end it costs less. Consider it because it can grow with the complexity of the tasks you ask it to perform and grow with your ability to use it. No, it’s not cheap. But it’s not a delusion either. From the very beginning, Sol small computer systems were designed to be at the very top of the microcomputer spectrum. We designed them so you wouldn't have to add costly extras to do many Jobs. We designed them so you could add quality peripherals and more memory to take care of more complex tasks. We designed them Circle 305 on inquiry card @ OU In. to use the best fully supported disk operating system on the market today, PTDOS, which we also designed. We designed them to use our Helios II mass memory. And for Sol small computer systems we designed new and adapted existing software to give you the choice of the best on the market today. Build computer power with our software. No system is complete without software, and at Processor Technology we have tailored a group of high level languages, and assembler and other packages to suit the wide capabilities of our hardware. Take a look at our exclusive Extended BASIC as an example. In cassette form, this BASIC features string and advanced file handling, special screen commands, timed input, complete matrix, logarithmic and trigonometric functions, 8 digit precision and square root. The language handles serial access files, provides tape rewind and offers cursor control for graphics capability. The disk version has all the number crunching talents of the cassette BASIC plus instant access to data and programs on floppy disks. It includes random as well as sequential files and a unique ability to update sequential data in place. Processor Technology FORTRAN is similar to FORTRAN IV and has a full set of extensions designed for the “stand alone” computer environment. Thousands of special application programs available through books and periodicals have already been written in this well established language. Processor Technology PILOT is an excellent language for teachers. It is a string-oriented language designed expressly for interactive applications such as programmed. instruction, drill and testing. No wonder we call it the serious solution to the small computer question. It’s the small computer system to do the general ledger and the payroll. Solve engineering and scientific problems. Use it for word processing. Program it for computer aided instruction. Use it anywhere you want versatile computer power! Sold and serviced only by the best dealers. Sol Systems are sold and serviced by an outstanding group of conveniently located computer stores throughout the United States and Canada. They are also available in Australia, Europe, the United Kingdom, Central America, South America, Japan and Singapore. For more information contact your nearest dealer listed on the following page. Or write Depart- ment B, Processor Technology Corporation, 7100 Johnson Industrial Drive, Pleasanton, CA 94566. Phone (415) 829-2600. In sum, all small computers are not created equal and Sol users know it to their everlasting satisfaction. ProcessorTechnology BYTE November 1978 9 See Sol’ at all these fine computer centers ‘AL: Birmingham: ICP Computerland, (205) 979-0707. GA: Berkeley: The Byte Shop. (415) 845-6366 Citrus Heights: Byte Shop. (916) 961-2983. Costa Mesa. Orange County Computer Center. (714) 646-0221. Hayward Computerland of Hayward, (415) 538-8080 Lawndale: The Byte Shop. (213) 371-2421 Modesto: Computer Magic, (209) 527-5156 Mountain View: Digital Deli, (415) 961-2670 San Francisco: Computer Center. Inc., (415) 387-2513, San Rafael: The Byte Shop, (415) 457-911. Walnut Creek: The Byte Shop. (415) 933-6252 _ CO: Boulder: Byte Shop. (303) 444-6550. Denver: Byte Shop, (303) 399-8995, CT: Bethel: Technology Systems, (203) 748-6856. FL: Ft. Lauderdale: Byte Shop of Ft. Lauderdale, (305) 561-2983. Miami: Byte Shop of Miami, (305) 264-2983, Tampa: Microcomputer Systems, Inc., (813) 879-4301. IL: Lombard: Midwest Microcomputer, (312) 495-9889. 1A: Davenport: Gomputer Store of Davenport. (319) 386-3330. KY: Louisville: Martronix Associates, (02) 459-0500. MD: Towson: Computers Ete. {301} 296-0520._MN: Minneapolis: Computer Depot. (612) 927-5601. MO: Florissant Computer Country. (314) 921-4434 NH: Nashua: Computeriand of Nashua, (603) 889-5238. NJ: Cherry Hill: Computer Emporium. (609) 667-7555, Iselin. Computer Mart of New Jersey, (201) 283-0600. NY: Endwell: The Computer Tree. (607) 748-1223. New York Computer Mart of New York. (212) 686-7923. White Plains: The Computer Corner, (914) 949-3282. NC: Raleigh: Roms 'N’ Rams, (919) 781-0003. OH: Akron: The Basic Computer Shop. (216) 867-0808. Columbus: Byte Shop. (614) 486-7761, Dayton: Computer Mart of Dayton, (513) 296-1248. “OR: Beaverton: Byte Shop Computer Store. (503) 644-2686 Portland. Byte Shop Computer Store. (503) 223-3496 Salem: Computer Pathways, (503) 399-0534. PA: King of Prussia: Computer Mart of Pennsylvania, (215) 265-2580. Ri: Warwick. Computer Power, Inc., (401) 738-4477 SC: Columbia’ Byte Shop, (803) 771-7624 TN: Kingsport: Microproducts & Systems, (615) 245-8081 TX: Arlington: Computer Port. (817) 469-1502 Ariington: Micro Store, (817) 461-6081. Houston: Interactive Computers, (713) 772-5257. Houston: Interactive Computers, (713) 486-0291. Lubbock: Neighborhood Computer Store, (606) 797-1468. Richardson Micro Store, (214) 231-1096. UT: Salt Lake City: Home Computer Store. (801) 484-6502 WA: Bellevue: Byte Shop Computer Store. (208) 746-0651. Seattle: Byte Shop of Seattle. (206) 622-7196.” WI: Madison: The Madison Computer Store, (608) 255-5552, Milwaukee: The Milwaukee Computer Store, (414) 445-4260. DC: Washington: Georgetown Computer Emporium, (202) 337-6545. CANADA: London, Ontario: Computer Circuit Ltd. 737 Richmond St, (519) 672-9370 Toronto: Computer Mart Ltd 1543 Bayview St., {416) 484-9708. Vancouver Basic Computer Group Ltd . 1548 West 8th Ave. (604) 736-7474. ARGENTINA: Buenos ‘Aires: Basis Sistemas Digitales. Colombres 849-1-A, 93-1986 or 57-7177, AUSTRALIA: ‘Sydney: Automation Statham Pty. Lta., 47 Birch St., (02) 709.4144, Carnegie. Sontron Instruments, 17 Arawatta St, (03) 569 7867. BELGIUM: Bruxelles. SP B.C. Finncontact Sauare Larousse. 5. 2/345-98-95. COLUMBIA: Bogota: Video National, Diagonal No. 5-62.32 66 35-36-37. DENMARK: Copenhagen. Peter W. Holm Trading ApS. Sankt Annae Gade 34, Christianshavn, (01)543466._ GREECE: Athens Attikos, Inc., 41 Char Tricoupi TT. 145, 9604091 JAPAN: Tokyo: Japan Personal Computers, Ltd Yamamoto Bidg No. 11-18, (03) 375-5078 5079 MEXICO: Mexico City: Industrias Digitales. S.A de CV, Plateros 7-116, (905) 524-5132 PHILIPPINES: San Juan’ Integrated Computer Systems, Inc, LIMKETKA\ Bldg. Suite 118, Ortigas Ave., Metro Manila, 3113, 78-40-71.72 SWEDEN: Stockholm: Wernor Elektronik. Torsvagen 61, Box 72, (0)8717-62-88. UNITED KINGDOM: Huntingdon, England Comart, Ltd 24A Market Square. St. Neots. Cambridgeshire. (0480) 74356. VENEZUELA: Caracas Componentes ¥ Circuitos Electronicos TTLCA CA. Av Fco de Miranda. Los Ruices, Apartado 3223, 355591 10 BYTE November 1978. etters SCHEMATIC ENCOUNTER | had a close encounter of the third kind while trying to read and understand the schematics to a Teletype ASR33 — it was just awful. The engineers had their hands on it for some time when it was decided to change it over to a 20 mA loop, and | was the victim elected to do it. Do any BYTE readers know if there is a book that explains the ASR33 Teletype schematics in understandable terms? | know it took many years to make the simple hard to understand, but maybe someone out there said that enough is enough to this madness. Yes, I finally got the show on the road, but for awhile | was thinking: why me? Craig Mueller 10130 Sepulveda Blvd Mission Hills CA 91345 INTERPRETER INFORMATION WANTED | have just finished reading Osborne and Associates’ 8080A/8085 Assembly Language Programming book. Now | want to find something that shows how a BASIC interpreter is put together in assembly language. Ail the software supplied here does not even attempt to explain in anything but vague terms. The question is, where can I find literature like this? | would like some- thing that would actually run and some- thing not theoretical. | hope you can help. Hugh Shedd #8 3419 Portland Av S Minneapolis MN 55407 Contact Dr. Dobb's Journal of Calis- thenics & Orthodontia for information on what they have published in the past with respect to BASIC interpreters. Their address is POB E, Menlo Park CA 94025. PRAISE FOR BITS 1 do not write letters to editors often but this is one pleasant exception. About a week ago my daughter ordered a book for my birthday from BITS. The birth- day was only a week off and she asked for fast service. Not only did the book arrive exactly one week from the date that she sent her letter, but it was also wrapped in birthday paper with a bow. It arrived the day before my birthday. Both my daughter and 1 were quite delighted at such a personal touch. believe that the name of the person Continued on page 141 Circle 305 on inquiry card. 56 GREAT LOCATIONS Computerland’ NOW OPEN: ALABAMA Huntsville CALIFORNIA Dublin El Cerrito. Hayward Los Altos Los Angeles Mission Viejo San Bernardino San Diego San Francisco San Jose San Mateo Santa Rosa Thousand Oaks Lawndale Tustin Walnut Creek COLORADO Colorado Springs Denver CONNECTICUT Fairfield DELAWARE Newark FLORIDA Boca Raton Ft. Lauderdale GEORGIA Atlanta Hawall Honolulu ILLINOIS ‘Arlington Heights Downers Grove Niles Oak Lawn Peoria INDIANA Indianapolis KENTUCKY Louisville MARYLAND Rockville MICHIGAN Grand Rapids Southfield MINNESOTA Bloomington NEW HAMPSHIRE Nashua NEW JERSEY Cherry Hill Bergen County Morristown NEW YORK Buffalo Ithaca NO. CAROLINA Charlotte OHIO Cleveland OREGON Portland PENNSYLVANIA Harrisburg TEXAS Austin Datias Houston WASHINGTON Bellevue Federal Way Tacoma WASHINGTON, D.C. 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BEFORE YOU BUY COMPUTER’ I, WisiT’1 COMPUTERLAND « j If the truth is that you want a computer . . . then we want to be your computer store. We're ComputerLand, the #1 computer store chain in the U.S. What's meaningful about that fact is, that ComputerLand has been chosen by more people as having what they've been looking for. And, since you're looking, let us tell you what you'll find, when you visit a ComputerLand store. You'll find a product line that's continually evaluated to provide you with the widest and best selection in quality, brand name microcomputers anywhere. You'll find an enthusiastic and knowledgeable staff able to interpret all the equipment specifications, in terms of how they apply to you, and in a way you'll understand. You'll find demonstration areas where you can get a firsthand experience of running a computer yourself. You'll find educational materials to give you a total insight into the world of microcomputers. You'll find a fully equipped service department to provide whatever assistance is required to keep your computer running in top-notch condition. You'll find computer user's clubs to join, where you can share ideas with people as enthusiastic as yourself. And, with each new visit, you'll find excitement—from the people you deal with, the equipment they offer, and from your own ever-growing personal involvement. Enough about us. How about what computers do. To attempt to describe all the things your computer might do, would be to describe your imagination. So instead, we'll briefly list some of the many things for which small computers are already being used. In business, the advent of the versotile and compact microcomputer has put the benefits of computing within reach of small companies. With systems starting at less than $6000, the businessman can computerize things like accounting, inventory control, record keeping, word processing and more. The net result is the reduction of administrative overhead and the improvement of efficiency which allows the business to be managed more effectively. In the home, a computer can be used for personal budgeting, tracking the stock market, evaluating investment opportunities, controlling heating to conserve energy, running security alarm systems, automating the garden's watering, storing recipes, designing challenging games, tutoring the children . . . and the list goes on. In industry, the basic applications are in engineering development, process control, and scientific ond analytical work Users of microcomputers in. industry have found them to be reliable, cost- effective tools which provide computing capability to many who would otherwise have to wait for time on a big computer, ‘or work with no computer at all COMPUTERS FOR INDUSTRY ‘And now we come to you, which leads us right back to where we started: If you want a computer, then we want to be your computer store. Whether you want a computer for the home, business or industry, come to ComputerLand first. We'll make it easy for you to own your first computer. Because, simply put, we really wont your business. When you come right down to it, that’s what makes us #1. Computerland’ WE KNOW SMALL COMPUTERS 14400 Catalina St., San Leandro, CA 94577 (415) 895-9363 + Franchise Opportunities Available BYTE November 1978-11 W.. personal computer will be most enjoyable and rewarding for you? Since we delivered our first Apple® IT in April, 1977, more people have chosen our computer than all other personal computers combined. Here are the reasons Apple has become such an overwhelming favorite. Apple is a fully tested and assembled mainframe computer. You won't need to spend weeks and months in assembly. Just take an Apple home, plug it in, hook up your color TV* and any cassette tape deck —and the fun begins. To ensure that the fun never stops, and to keep Apple working hard, we've spent the last year expanding the Apple system. There are new peripherals, new software, and the Apple II Basic Programming Manual. And wait till you see the Apple magazine to keep owners on top of what's new. Apple is so powerful and easy to use that you'll find dozens of applications. There are Apples in major universities, helping teach computer skills. There are Apples in the office, where they’re being programmed to control inven- tories, chart stocks and balance the books. And there are Apples at home, where they can help manage the family budget, control your home’s environ- ment, teach arithmetic and foreign languages and, of course, enable you to create hundreds of sound and action video games. When you buy an Apple II you're investing in the leading edge of tech- nology. Apple was the first computer to come with BASIC in ROM, for example. And the first computer with up to 48K bytes RAM on one board, using advanced, high density 16K devices. We’re working to keep Apple the most up-to-date personal computer money can buy. Apple II delivers the features you need to enjoy the real satisfaction a personal computer can bring, today and in the future. s & hi-resofution graphics, too. Don’t settle for a black and white display! Connect your Apple to a color TV and BASIC gives you instant command of three display modes: Text, 40h x 48v Color-graphics in 15 colors, and a 280h x 192v High Resolution array that lets you plot graphs and compose 3-D images. Apple gives you the added capability of combining text and graphics, too. Back to basics, and assembly language too. Apple speaks three languages: fast integer BASIC, floating point BASIC for scientific and financial applications, and 6502 assembly language. That’s maximum programming flexibility. And, to preserve user’s space, both integer BASIC and monitor are permanently stored in 8K bytes of ROM, so you have an easy-to-use, universal language instantly available. BASIC gives you graphic commands: COLOR=, VLIN, HLIN, PLOT and SCRN. And direct memory access, with PEEK, POKE and CALL commands. Software: Ours and yours. There's a growing selection of pre- programmed software from the Apple Software Bank — Basic Finance, Checkbook, High Resolution Graphics and more. Now there’s a User Section in our bank, to make | it easy for you to obtain programs developed by other Apple owners. Our Software Bank is your link to Apple owners all over the world. Alive with the sound of music. Apple’s ex- clusive built-in speaker delivers the added dimension of sound to your programs. Sound to compose electronic music. Sound to liven up games and educational programs. Sound, so that any program can “talk” back to you. That’s an example of Apple’s “people compatible” design. Another is its light, durable injection-molded case, so you can take Apple with you. And the professional quality, typewriter-style keyboard has n-key rollover, for fast, error-free operator interaction. Apple is the proven computer. Apple is a state-of-the-art single board computer, with advanced LSI design to keep component count to a minimum. That makes it more reliable. If glitches do occur, the fully socketed board and built-in diagnostics sim- plify troubleshooting. In fact, on our assembly line, we use Apples to test new Apples. Apple Il plugs into any standard TV using an inexpensive modulator (not included). n California, call 408/996-1010. Apple peripherals are smart Watch the far right column of this ad each month for the latest in our grow- ing family of peripherals. We call them “intelligent interfaces.” They’re smart peripherals, so you can plug them in and run them from BASIC without having to develop custom software. Noother personal computer comes close to Apple’s expandability. In addi- tion to the built-in video interface, cas- sette I/O, and four A/D inputs with two continuously variable game paddles, Apple has eight peripheral slots, three TTL inputs and four TTL outputs. Plus apowerful, state-of-the-art switching power supply that can drive all your Apple peripherals. Available now. Apple is in stock and ready for delivery at a store near you. Call us for the dealer nearest you. Or, for more details and a copy of our “Consumer's Guide to Personal Computers,” call 800/538-9696** or write Apple Computer, Inc., 10260 Bandley Drive, Cuper- / \ tino, CA 95014. liry card. woppic computer’ Programming is a snap! I'm halfway through Apple’s BASIC nanual and already I've programmed M4 my own space wars game. Those math programs | wrote last week-—I just rewrote them using Apple's mini-assembler and got them to run a hundred times faster. New from Apple. Valuable new series of software packages for investors Now private investors can generate their own stock market reports and per- form critical investment analysis instantly with Apple II. Just log your Apple II computer on to Dames central data bank with powerful Apple software: the Dow Jones Series. The first two of these highly practical programs are available now. ple’s Stock porter ~~ program, a local tele- ror phone call links you to Dow Jones’ continuously updated stock quotes for more 6000 com- ma : panies listed on six major U.S. exchanges. Current activity for stocks in the investors portfolio is delivered automatically: ask/open, bid/close, high, low and last prices, and volume traded. Our Portfolio Evaluator enables you to analyze current value of your portfolio, and short- and long-term gain/ loss for each stock—or for your entire folio. Cost of Apple’s Dow Jones service is a one time contract fee of $25, which includes the Stock Quote Reporter pro- . An additional $3 cl is made for the first three minutes of any transac- tion and 50g per minute thereafter. To take advantage of Apple’s new financial services, Apple II users need only a etreerelery Gur modem and an ordinary telephone. This equip- ment, the Dow Jones Series, and a broad selection of other Apple software are now in stock at your local Apple dealer. Circle 15 on inquiry card. Apple's smart peripherals make expansion easy. Just plug ‘em in and they're ready to run. I've already added two disks, a printer and the communications card. DYNABYTE COMPUTERS ARE ALL BUSINESS INSIDE AND OUT. When we designed our new small business computers, we meant busi- ness. As basic as that seems, it is unique. Just about every other microcomputer being sold as a small business system today was originally designed as a kit for hobbyists. Every design decision was made with quality and reliability in mind. The result is dependable performance and a solid appearance for business, profes- sional and scientific applications. FIRST SMALL SYSTEM WITH BIG SYSTEM STORAGE Many applications handle large quantities of information, so the DB8/2 uses two quad density S-inch disk drives with our exclusive Dual Density Disk Controller for up to 1.2 megabytes of formatted storage. That's more capacity than two single density 8-inch drives. If you need more storage, our DB8/4 has two 8-inch drives with up to 2 megabytes capacity, more than any other dual floppy disk system on the market. OUR SOFTWARE BIG ON BUSINESS Dynabyte helps you get down to business immediately. The DB8/2 is the first microcomputer to offer enough storage capacity on S-inch drives to fully utilize CP/M,* the most widely accepted disk operating system. We also supply and support BASIC, FOR- * CPIM isa trademark of Digital Research TRAN and COBOL programming lan- guages. Our applications packages in- clude general ledger, accounts receiv- able, word processing and many other CP/M compatible programs. Reliability is a big consideration in buying a business computer, so we built it in. Our edge connectors meet military specifications, the toughest electronics manufacturing standard. Our regulated power supply is designed to meet U.L. standards, which means the entire sys- tem muns cool and dependable. And our cast aluminum enclosures are rugged as well as attractive. AND THE BIGGEST THING OF ALL Customer support. Our support starts at the factory with testing and bum-in programs that assure the entire integrated system is reliable prior to shipment. Our completely modular de- sign allows continuing support in the field. We maintain a bonded inventory of all sub-system modules which means we can deliver replacement sub- assemblies overnight nearly anywhere in the continental U.S. Dynabyte built in little things, too. Like a fully-populated 12-slot backplane, switched AC outlets for ac- cessories, an option for European power, quiet whisper fans with long-life metal construction, lighted indicator switches for Power On and Halt, a shielded enclosure to protect disk drives from electro-mechanical interference, and a fully enclosed power supply for operator safety. Since we didn’t cut comers in de- sign, the price/performance ratios of our systems make good business sense. THE INSIDE FACTS The DB8/2 Computer System in- cludes two 5-inch disk drives either single or double sided for up to 1.2 megabytes of mass storage, a 4MHz Z-80 processing module with one parallel and two serial ports, an EPROM programmer and up to 4k ROM; 32k of RAM, a 12-slot fully- populated backplane; our exclusive Dual Density Disk Controller, and CP/M. The DB8/1 Computer includes a 4MHz Z-80 processor with one parallel and two serial I/O ports, an EPROM programmer and up to 4k of ROM; 32k RAM, and a 12-slot fully-populated backplane. The DB8/4 Disk System, designed to be the mass storage companion to the DB8/1, includes two 8-inch floppy disk drives in either single or double sided configuration for up to 2 megabytes of mass storage, our Dual Density Disk Controller, and CP/M. All three units will be available in rack mount models. For a descriptive brochure and price list, call or write Dynabyte, 1005 Elwell Court, Palo Alto, CA 94303. Phone (415) 965-1010. Or better yet, see your local dealer. DINABYTE YOU CAN DEPEND ON IT. Circle 110 on inquiry card BYTE November 1978 15. An Exchange Evaluator for Computer Chess Dan and Kathe Spracklen 10832 Macouba PI San Diego CA 92124 Three main tasks are basic to computer chess: generation of moves, evaluation of positions and selection between alternatives. Of these three, the central determining factor in the strength of the program relative to the capacity of the host machine is the eva/ua- tion segment. The reason for this is that any program must come to grips with the task of move generation, and various tech- niques of “pruning” decision trees are by now widely known. Furthermore, the smaller and slower the host machine, the more importance must be assigned to the evalua- tion facility. If a search can be carried to a great depth of p/y, inaccuracies can generally be corrected long before the machine has been committed to a costly line of play. (A ply is a move by one player, ie: half of a complete move involving both players.) On the other hand, if processing limitations White Black Byte Byte Count Cx 1 8 Pawns ag " 2 9 Knights | 3 10 Bishops | 4 1" Rooks 5 12 Queen 6 13 King 7 14 Bt 76543210 Bt 76543210 Table 1; Format of the attacker’s array, a 14 byte array divided into two sec- tions, seven bytes for White and seven bytes for Black. The first byte of each section contains the number of attackers (or defenders) in the array. The other six bytes contain the values of the pieces participating in the attack un- der analysis. Since no more than four bits are required per piece, two pieces are stored per byte and the array has a fixed format. The routine that fills the array assigns the first attacker of a given type to the low order four bits of the byte. A subsequent attacker of the same type is added by shifting up the low order four bits and inserting the new attacker. 16 November 1978 © BYTE Publications Inc. prevent a critical exchange from being examined to its conclusion, then not just accuracy but clairvoyance is demanded. Thus an attack evaluator assumes tremendous importance in a microcomputer chess pro- gram, much more so than in a large scale machine. But the limitations placed on the programmer of an 8 bit machine make it correspondingly more difficult to achieve this type of predictive power. The ability of Sargon (a chess playing program we wrote in Z-80 assembler language) to accu- rately forecast the outcome of an exchange has been the greatest single factor in its success. Some Tactical Considerations First, consider the capabilities desired of the routine. Assume that the computer is faced with evaluating the board position in figure 1. Black possesses a dangerous passed pawn that White has blockaded with a Knight. White is piling up attackers on the pawn and presently assaults it with King, Queen, and from behind the Queen, a Bishop: a total of three attackers. Black defends with Queen, Rook, and Knight; but the Black Knight is pinned against the Black King by White’s Bishop, so Black really only has two usable defenders. Does this mean the pawn is lost? No, consider the order in which the exchange would occur. The King cannot legally capture first and the Bishop is behind the Queen, so the Queen must be the first taker. When Black responds with Rook takes Queen, Black has gained considerable material and is under no obliga- tion to go any further with the exchange. To summarize the subtleties involved, the program must recognize transparent attacks through its own pieces which move in the same direction. It must recognize pins (and partial pins such as a Rook pinned along a rank or file). It must understand the relative values of attacking and defending pieces, and, finally, it must realize that the exchange may be terminated at any point by either side. Pins are a whole topic in themselves, and Sargon’s pinned piece routines will not be discussed in any detail. Instead, we shall concentrate on the exchange routine itself, which weighs the relative merits of the battles engaged on the board. The Data Structures The basic data structure used by the ex- change evaluator is the attackers array. It is a 14 byte area divided into two sections, seven bytes for White and seven for Black. The first byte of each section contains the number of attackers (or defenders) con- tained in the array. The other six bytes in each section store the piece values of the pieces participating in the attack. Since no more than four bits are required, two pieces are stored per byte, and the array has a fixed format. Table 1 illustrates the arrangement within a section. The routine which fills the array assigns the first attacker of a given type to the low order four bits of the byte. A subsequent attacker of the same type is added by shifting up the low order four bits and inserting the new attacker in its place. The instruction used to implement this is the rotate left digit (RLD) (see figure 2). If a piece attacks from behind the Queen, such as the Bishop in figure 1, it is placed in the high order four bits of the Queen byte. From that position it will not come into play in the attack until after the Queen has captured. It is possible for two Rooks to attack through the Queen. In this situa- tion one Rook is stored behind the Queen and the other in the King byte, pushing him up behind the Rook if he is involved in the attack. (By the rules of chess, the King can- not capture unless all defenders are ex- hausted, so he is properly placed behind the Rook.) A note about overflows: the table is nec- essarily limited in size and is adequate for all the pieces originally on the board. If pawn promotions result in multiple pieces and a table overflow occurs, the excess pieces are ignored in evaluating the exchange. An Overview of the Exchange Evaluator The exchange evaluator (XCHNG) oper- ates on a prefilled attacker’s array. The array itself is filled by the attack save (ATKSAV) routine as attackers are dis- covered by the attacker's routine (ATTACK). The latter two routines are important, and recent changes to them have resulted in a significant improvement in the performance of Sargon, but they are not discussed in this but bat Y “Yip article. The attacker's array describes a specific battle over a given occupied square. The player who occupies the square is the defender and the player with the opposite color is the attacker. The attacker’s section is examined for the lowest valued attacker. That piece is compared in value to the piece on the occupied square. If the attacker is lower in value than the defended piece, we know at once that we can win material by capturing that piece. We don't yet know how much, because the piece may have been totally undefended, or it may be that our lower value piece will be captured in return. For example if our Bishop attacks an enemy Rook, we can be sure at least of “winning the exchange” (a phrase chess buffs use to describe trading a Rook for a minor piece, ie: for a Bishop or Knight). But to find out whether the whole Rook is ours for free or if we must give up our Bishop in return, we must toggle the attacker/defender roles, since our Bishop now occupies the square, and run through the analysis again. Of course back when the Bishop was retrieved from the attacker's array, it was also re- moved, the attack count decremented, and its position filled with zeroes. The evaluation is not so obvious when the attacker is of higher value than the piece ‘on the occupied square. In this case there are only two situations in which you would want to capture. One occurs when the at- tacked piece is totally undefended, and the AccumULATOR | _ als Si (REGISTER A) MEMORY ? lis ° LOCATION Figure 1: Sample board position. White’s Bishop is indirectly attacking the pawn, so the value of the Bishop is stored in the high order four bits of the Queen byte (which is directly attacking the pawn) in the attacker's array. See table 1. Figure 2: The Rotating Left Digit (RLD) instruc- tion, used to add attackers to the attacker's array. November 1978 © BYTE Publications Inc 17 Figure 3: Summary of the flow of exchange evalu- ation. If the attacker is of the same value as the piece under potential attack, material cannot be lost by swapping, and the piece may in fact be taken for free. To determine the potential for winning material, assume the cap- ture takes place, switch (or “toggle”) the roles of defender and attacker and run through the analysis again. FETCH ATTACKER AND COMPARE TO PIECE CHALK UP POINTS GAINED CHECK VALUE F DEFENDER OF LOWER VALUE THAN ATTACKER AND TOGGLE The use of computers for industrial automation is sky- rocketing, and engineers are needed to design them. If you're stalled in your present position, we have the opportunities to challenge you. If you are a degreed engineer with hardware or software design experience, call or write Dick Conklin, (216) 943-5500. Babcock & Wilcox Bailey Controls Company 29801 Euclid Ave. Wickliffe, Ohio 44092 An Equal Opportunity Employer M/F Circle 27 on inquiry card. other occurs when the attacked piece is defended by a piece of the same or higher value, and we can back up the attack with yet another attacker. Suppose, for example, our Queen attacks an enemy pawn. If the pawn is completely unguarded, we can, of course, take it for free. We might also want to take it if it is defended by the opponent’s Queen and we can recapture with, say, a Bishop which attacks from behind our Queen. But any time the attacked piece is defended by a piece of lower value than the attacker, we can terminate the exchange right there, since it would not be to the advantage of the attacker to continue. For example, if our Queen attacked a pawn that was defended by an enemy pawn, we wouldn’t consider making the capture. If the attacker is of the same value as the piece on the occupied square, we know we can’t lose material by swapping, and the piece might be ours for free. So to find out what we stand to gain, we assume the cap- ture takes place, switch (or ‘‘toggle’”’) the attacker/defender roles, and run through the analysis again (see the summary in figure 3). Quantizing the Evaluation We now have a general plan for the flow of the evaluator. What is needed is a means of quantizing the results and coming up with a points total, the exchange residue, which accurately describes that particular battle. The exchange residue is zero at the onset of the analysis and will be adjusted up or down as the evaluation proceeds. At each iteration the number of points at stake is the value of the piece which cur- rently occupies the square in question. If the analysis calls for a capture on the first iteration, the points at stake are added to the exchange residue. Thus the exchange residue will contain the number of points lost by the initial defender (or, conversely, won by the initial attacker). We will main- tain this frame of reference throughout the evaluation. If the analysis requires that attacker/defender roles be toggled, and a capture occurs on the second ‘iteration, the points at stake would be subtracted from the exchange residue. Suppose we again have a situation where our Bishop attacks an enemy Rook. The points at stake are the assumed value of the Rook, and let’s suppose we value the Rook at five points. We know the analysis will call _ for Bishop takes Rook, so at that time the five points for the Rook will be added to the initially zero exchange residue. Then And it’s all yours for $995. We ‘even offer CP/M for just $70, Micro-Soft Extended Disk Basic for just $199 and Micro- ‘Soft Fortran for just $349 as nice options to add to your library. No wonder it's an overnight success! See DISCUS 1™ today at your local computer shop. Or if unavailable locally, send your check or money order direct to Thinker Toys™ {add $7 for handling; California residents add tax.) 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BYTE Ssomermber 19% 19 BLACK Attackers Array: > 7 Count 3 2 7 7e] = th Awe (ar —— Bishops 3 pts YY oe a Yi) Queen 9 pts A Y King “id White Black 2 Yh; & Yl Points | Attacker's | Defender’s | Exchange Yi At Stake Value Value Residue Onset - - - 0 3 3 1 3 First (Black (White (Black Black WHITE Iteration Knight) Knight) Pawn) Defends (SARGON) 3 1 3 0 Second (White {Black (White White White to play. Iteration Knight) Pawn) Knight) Defends 1 3 9 1 Third (Black (white (Black Black Values used are based on the scale: Iteration Pawn) Knight) Queen) Defends Queen 9 points 3 9 3 No Change* Rook — 5 points Fourth (White (Black (White White Bishop 3 points Iteration Knight) Queen) Bishop) Defends Knight 3 points Pawn 1 point *Black will not continue at the cost of his Queen. Figure 4: Analysis of a typical chess battle, in this case at the K4 square, ta- ken from the game of Keres versus Najdorf, International Tournament at Margate, 1939. The associated chart shows how the points at stake, attacker's value, defender’s value and exchange residue are altered at each successive iteration. 20 November 1978 © BYTE Publications Inc the attacker/defender roles are toggled, and if our Bishop, worth say three points, is recaptured, those three points would be subtracted from the exchange residue leaving a current residue of two points. If the battle continues, on the third iteration the points are again added, and on the fourth sub- tracted, etc. Figure 4 gives a typical battle and the associated chart shows how the points at stake, attacker’s value, defender’s value and exchange residue are altered at each successive iteration. A note on the bounds of the exchange residue is pertinent here. The exchange res- idue will always be a positive number. This is clearly so, since for it to go negative the attacker would have to engage in an unsound exchange, such as the Queen capturing a pawn defended by another pawn as in a pre- vious example, Such an exchange would be a blunder. We will assume that this won’t occur on the part of our opponent, and we will eliminate it from our moves. The ex- change residue will also have as a maximum the number of points at stake initially, since the defender will not make a move that will cost more than has already been lost. Thus, 0 < exchange residue < value of attacked piece. Programming the Evaluator Great care is necessary in coding the routine, since it must be executed once for every attacked piece on the board. If we assume that an average of five pieces will be under attack at a time, this means the routine will be executed five times for every board evaluated. Since typically 5,000 to 12,000 board positions will be evaluated by the most recent version of Sargon using a 4 ply search, this means the exchange evaluator may be executed up to 60,000 times in determining a single move. So an inefficiency in execution time as sl needlessly pushing and popping four registers would be magnified to a total cost of three seconds (assuming a 2 MHz clock) in the time required to process a single move. For this reason chess programmers must quickly become familiar with the relative execution times of their machine’s instructions. If the exchange evaluator seems obscure, the Micromation has done for the 5-100 bus what IBM did for the floppy disk. TOE Wt ALU LWW KR AE L lise doubled Scapecity: Double Capacity The DOUBLER — Micromation’s latest advance in floppy disk technology — doubles the capacity of floppy disk systems. Over 500 KBytes are recorded on each side of an 8" disk. This means bigger files for more powerful systems. Double Speed Data transfer with the DOUBLER is twice as fast — 500 Kbits per second. And since there is twice as much data on each track, your drive steps only half as much — so your system runs faster than it ever has before! Increased Reliability That's right — even better reliability. Why? Because we did it the IBM way. IBM designed 2D formatting — so it has to be reliable. Micromation's innovative, state-of-the-art de- sign incorporates write precompensation electronics and a phase lock oscillator on a single, all digital, 5-400 circuit board. So we guarantee the DOUBLER will be more de- pendable than your present single density controller — and ‘we warantee the DOUBLER for a full year. Unbeatable Convenience It couldn't be easier to step up to double density. The DOUBLER operates automatically in either single or double density. Just insert a diskette and you're running properly. You can transfer files between single or double density diskettes without any software or hardware changes — or even oper- ate with one single and one double density diskette. Installation is a snap. There’s a hardware UART on board and the software is all ready to go. An onboard 2708 EPROM contains the bootstrap. There's even jump-on-reset circuitry so you can operate without a front panel. And, of course, we include utilities to format diskettes Universally Versatile The DOUBLER will operate with all industry-standard mini and full-sized drives. And it will work in any 8080 or Z-80 5-400 computer operating at 2 to 4 MHz. The DOUBLER will support up to four double or single headed drives. Fully Compatibie The DOUBLER is compatible with CP/M* version 1.4. If you have a CP/M* 1.4 system, just add our CBIOS — or you can buy our ready-to-boot version. Install the new controller, connect any terminal to the RS-232 interface, and boot off your new double-sized, double-speed system. You still can use all your old software without any changes Completely Affordable All Micromation products are fully assembled, thoroughly tested, include complete documentation, and are priced for value: DOUBLER double density controller $ 495. MEGABOX dual drive double density system 2,295. ZEPHER — Per Sci double density system 2,595. Z-PLUS — MEGABOX 32 KZ-80 computer 4,295. Available The DOUBLER is available NOW at your local computer store. Micromation Inc. 524 Union Street San Francisco California 94133 / 445 398-0289 Where there’s always more in store. Circle 223 on inquiry card. *CP/Mis 0 trademark of Digital Research. BYTE November 1978 21 blame lies in just such considerations. Since nearly every register in the Z-80 RE “f | Program Status’ processor is utilized in the routine, a map {Various Uses) Flags is provided for reference in the discussion Be Defender awoke (see table 2), Although Sargon is coded in Count Count. Z-80 assembler language using TDL mne- : am monics, no prior knowledge of the specific E ‘ttacker Section Address e ee B _ “a pes instructions is assumed. However, it is HL Defender Section Address assumed that the reader is familiar with i some microprocessor assembly language. Ix Index to Value Arra a . = a Two routines are described: XCHNG, which Vv rforms the actual evaluation, and Table 2: Map of the re- pe B gisters used vy the ex- NEXTAD, which searches the attacker’s change evaluator. _ . array for the next attacker or defender. AF’ < Program Status . . Defender Flags. Using the Exchange Residue Bc’ Attacked " Flag to 2 Piece Value Defender Side The exchange evaluator has completed its "Each work once it has returned the outcome of De’ ‘Residue the battle. But the evaluation segment is by: —— no means complete. Information gleaned HU ‘ Attacker by analyzing attacks must be blended with = data concerning piece mobility, develop- ment, total material and any other heuristics included in the program. The total picture is Table 3: Map of the BC. the responsibility of a routine called DE and HL raglan used BC Levers Defender POINTS, which is not discussed here. But it by the attacker|defender - is useful to see how POINTS makes use of Joutines DE ” Befender Section Aadrew, the information returned by XCHNG. . : : The exchange evaluator must be called HL . i d Acker Seorion Adaress to examine every potential battle on the Label OpCode Operand Commentary XCHNG: LDA PL Hes the attacked piece into register A. e piece includes a color Age in bit 7 ce “tor White, 1 for Black) and the piece a type in bits 2-0. Listing 1: The Sargon ex- LXI HUWACT Load into the HL and DE register pairs. change evaluator, written LXL D,BACT The pees oe the White and in Z-80 assembler language BIT 7A Test the color flag bit of the plece and with TDL mnemonics. SRZ XCS skip the XCHG if the piece is White. XCHG Otherwise swap the contents of the HL and DE registers. The result is to produce a pointer to the defender’s section of the attackers array in the HL register pair and a pointer to the attacker's prey ar in the XC5: MOV BM Fetches the byte pointed to by the HL pair LDAX D into the B register. Fetches the byte pointed MOV CA to by the DE pair into the A register, then moves it into the C register. the first byte if each section of the attacker's array is the count (see table 1), we now have the total number of defenders in register B and attackers in C, EXX Swap registers BC, DE, and HL for registers Note: A documented source a0 Bee ae ey samp listing of the entire Sargon an eee program is available for $15 MVI c,0 Register C contains a flag which tells ae from Dan and Kathe Sprack- the attacker/defender roles have len, 10832 Macouba PI, San Soe time ti roles cep Ceres Diego CA'92128.. bit 0 of C, we can tell which side is being examined. A value of 0 indicates the at- tacker’s side is under consideration, and a value of 1 the defender's side. MVI EO Initialize the exchange residue. LIXD TS. 3 is an index by piece type into an array, MOV B,PVALUE(X) called PVALUE, which contains 22 November 1978 © BYTE Publications Inc ia y 1 lee? a) aa Learning by doing is still the best method of education. And when it comes to learning about the world of microcomputers, you won't find a better method than the Instructor 50. It’s the fast, ready-to-use learning device that immediately provides “hands on” experience for gaining microprocessor knowledge—in your home, office, or in the classroom. Superior to other microprocessor learning aids, the Instructor 50 is a COM- PLETE package—including a Palen spares, supply (50/60 Hz), an LED prompting display, and both functional and heckaeriinal keyboards, You also get S-100 compatibility for adding memory and other peripherals. This lets ou expand the machine's capability—and your microprocessing applications Cnuwietge. Moreover, you van eeuily bali a progr Grin Byeenn ied yacromn audio cassettes. ‘ The Instructor 50 comes complete with a Users’ Guide, along with step-by-step instructions for those with no previous microprocessor experience. Signetics offers one of the broadest choices of microprocessors in the industry. This knowledge stands behind the Instructor 50. When you need to learn about microprocessors, start with Signetics. Start with the Instructor 50, Send for your descriptive brochure today. We can help you understand microprocessors. Circle 317 on inquiry card. BYTE November 497) 2 Modern as Your Compiter A Solid Stét Solid state beer . has moved the ene F quchy ton the business world into personal uses. Meanwhile, comp ds have hardly moved at all. Now TASA introdu Bice as modern xed ie plac Don’t confuse it with ordinary flex switches. It is fully solid state -contained, ig in and use. Since it has no mechanical moving parts, it responds quickly to your touch. And it pi be set coding in TASA's exclusive color-keyed layout that makes it easier to say what you want to say to your computer. This is the TASA Micro Proximity Keyboard, and it sells for only $49.95. Despite the price, CMOS/LSI integrated circuits make it totally reliable inside. With the sensors behind a shield of polycarbonate —the most rugged plastic ever developed—it is also durable and reliable outside. The TASA Keyboard contains all the features you would expect in a professional keyboard—shift, shift lock, control functions, and a normal typewriter format. If you're tired of costly mechanical keyboards and kits you have to assemble, bring your computer up to date the easy way. Plug in a TASA Keyboard. It will never come between you and your computer. ae i a — | Micro Proximity Keyboard 7 (acs | | oc | (ac) {cca | sj | occ || | |e | om | a | amc} {econ || ecm} | com || cm | | tc | | cee | | comm) | mm | \ ceca ' U \\ bi} WH Hae The TASA Keyboard Features: 51 Keys, with entire 128 posi- tion ASCII code output. All keys identified as to Un- shift, Shift and Control outputs. Full 8-bit ASCII output with selectable positive or nega- tive parity. Single power supply, 12.5 - 20V unregulated. Output TTL, DTL and CMOS- compatible. Full solid state design with no moving parts. Standard PC edge connect- er. Use on any flat surface, or with Optional plastic support stand (as shown) a bo 0060070 =| Touch Activated Switch Arrays, Inc. 2346 Walsh Avenue, Santa Clara California 95050 (408) 247-2301 NAME. ADORESS: 1 a eee STATE zp Enclosed is my check for $ to cover: _—— TASA Keyboards @se— § _—_— Optional stands @si20— § Shipping and handling charge at $5.00 per keyboard— $ SUBTOTAL—$ _ Sales Tax, 6%—$ (California residents only) TOTALENCLOSED $ 9/78 Price subject to change without notice Circle 363 on inquiry card. XC10: ‘XC15: XC18: XC19: XC20: NEXTAD: NXS5: NX6: RZ MOV CALL EXAF MOV CMP JRNC EXAF RC CALL MOV MOV MOV XCHG IRZ DCR INX CMP IRZ RRD pcx EXX NEXTAD LA NEXTAD XC18 AB L XC19 NEXTAD LA NEXTAD XC15 AB 0c xc20 NXS The index is loaded into the IX index register and then the value of the piece un- der attack is loaded into the B register. So register B contains the number of points at stake in this attack, Getting the value of the next attacker in register A. NEXTAD also sets the zero flag if there are no more attackers, Return if no more attackers. Save the attackers value in the L register. Getting the value of the next defender in register A, fad setting the sero flag if no more def iho datecaler ‘the piece is lost. Go chalk up ts gained. the defender by swapping AF and AF’ Move the value of the attacked piece into the A register to then compare its value to that of the attacker. Branch to XC19 if the value of the attacker is not greater than the value of the piece, to chalk up points gained and toggle. To reach this point, the attacker must be it is necessary to consider the value of the defender. This instruction swaps A and A’ again to restore the value. Com} the value of the defender to the . If the defender is worth less, return. It will not be to the attacker's advantage to continue the exchange. Otherwise get the value of the next attacker. Returm if none. If the defender is worth the same or more than the attacker, the ex- change should continue, provided there is another attacker available to recapture. Save the new attacker's value in the L register. ‘Then find out if there are any more de- fenders to contend with. If so, jump back to XC15 and eae the process. ‘The exchange is terminated. There are no more defenders. The zero flag is set, so save it by swapping AF and AF’, Get the value of the attacked piece. Test for attacker's or fender’s side. Skip if on the attacker's side. Otherwise negate the value of the attacked piece. (On successive iterations the value is alternately added and subtracted.) ‘Add the previous residue to the new points won or lost and store the result as the new exchange residue. Restore the last defender and the zero flag. Return if there are no more defenders. The last attacker becomes the new defender, Move his value into the B register and return to XC10 for another iteration. Increment side flag. ‘Swap registers BC, DE, HL for BC’, DE’, HL’, getting the set that contains the at- tacker and defender counts. ‘Swap attacker and defender counts. ‘Swap attacker's array pointers. The register map is now as in table 3. Zero the A register and compare it to the attacker count. Go return if there are none, Otherwise decrement the count, since one will be removed from the array. Check the next byte of the attacker's array, looking for an attacker. If not in this byte, go check the next. register. "The rota i digit (RRB) is te e rotate it it ie reverse of the rotate left digit illustrated in figure 2. Decrement HL to back up the pointer. With two attackers stored per byte, the routine will return to the same byte to look for the next one. Swap registers BC, DE, HL and BC’, DE’ and HL’ back again. Return. November 1978 © BYTE Publications Inc 25, Figure 5: Potential problem arising from the author's evaluation scheme: White’s Knight is attacking the Black King and Rook, for which White gains 3/4 of the Rook's value. The Knight is doomed to be captured by Black's Queen, but subtracting the Knight’s value from this number still gives White an illusion of material gain. The authors avoided this problem by having the program check to see if the piece that has just moved is subject to capture. board for a given position. In some of the attacks, the side which has completed a move will have lost points. In others the side about to move will be in danger of losing material. As battles are evaluated one by one, the highest points lost for the side having moved is maintained. This value represents the amount of material this side stands to lose, and it is subtracted directly from the material score. Two scores are maintained for the side about to move: the highest points lost, and the second highest points lost. Both values are saved, because it is assumed that this side will always use its move to rescue its highest value piece. Then only 3/4 of the value is deducted for the loss of the second highest piece, since deducting the entire value would make attacks look as good as cap- tures (see the text box for an example of this procedure). Bonus points are given to each side for additional battles won, but this is still experimental and may not be needed. One problem that arose with this eval- uation scheme was the Knight's tendency to engage in useless forks. In figure 5 we see White’s Knight attacking the enemy King and Rook, for which White gains 3/4 of the Rook’s value. The Knight is of course doomed to be captured by the Queen and The Quiet Printer Telpar's 48-Column PS-48E... $350.00" KEY FEATURES INCLUDE: @ Microprocessor controlled © Versatile interface (no added charge) | Serial: AS-232C, 20 mil loop, or TTL Parallel: TTL interactive © Upper/lower case, 96 ASCII characters @ Throughput rate — 24 characters per second ™ Signalling rates Serial mode: 110 or 300 Baud Parallel mode: up to 960 cps | ® Automatic carriage return and line feed @ Thermal printing, no ribbons or ink In quantities of 100 ....... $350.00 Single quantity ........... $450.00 For more information contact Telpar, (214) 233-6631, 4132 Billy Mitchell Road, Box 796, Addison, Texas 75001. telpear, tno © Telex: 73-7561 (Teleserve) DAL. 26 November 1978 © BYTE Publications Inc Circle 372 on inquiry card. COSMAC VP $2.49 gets the entire family into creating video games, graphics and control functions. For starters. COSMAC VIP, the completely assembled, ready-to-operate RCA Video Interface Processor, opens up a whole new world of computer excitement. New challenges in graphics, games and control functions. Yet it’s just $249.00. Easy to buy. And easy to program, thanks to its unique, easy-to-use interpretive language. You get a complete how-to book including programs for 20 games: fun, challenging, and ready to load and record on your cassette. Simple but powerful. Built around an RCA COSMAC micropro- cessor, the VIP is a complete computer system that can grow with you. It has 2K of RAM, ex- pandable on-board to 4K. Plus a ROM monitor, audio tone output to a built-in speaker, power supply, and 8-bit input and output ports for control of relays, sensors, or other peripherals. Circle 322 on inquiry card. Soon RCA will offer options for color graphics and 256 tone sound generation. An optional auxiliary keyboard Hp an exciting world of two-player will ope games. Take the first step now. Check your local computer store or elec- tronics distributor for the VIP. Or contact RCA VIP Marketing, New Holland Avenue, Lancaster, PA 17604. Phone (717) 291-5848. “Suggested retail price. Does not include video monitor or cassette recorder. BYTE November 1978 27 The fun way into computers. Table 4: Second order at- tacks. This type of attack, including pinned pieces, overworked pieces, dis- covered attacks, and so on, is not considered in the exchange evaluator de- scribed in this article. BLACK Zz 7 i. yim jj, WY ‘My WHITE (SARGON) Making an Immediate Capture More Attractive Than an Attack In the diagram, the program (White) has two attractive moves: capture the Bishop, or move the Knight so that it simultaneously attacks the Black Rook and the second Bishop. The program assumes that in the latter case Black will protect the Rook (the more valuable of the two pieces) by moving it away. The decision then reduces to one of capturing the first Bishop or simply attacking the second Bishop. In order to insure that the capture takes place, the program assigns 3/4 the normal value to the second Bishop so that the capture looks more attractive. The drawback to this technique is that it precludes the possibility of intentionally avoiding an immediate capture for strategic purposes; this would require a much more complicated program, of course. can never carry out its threat, but sub- tracting the Knight’s value still gives White an illusion of material gain. Sargon avoids this problem by checking to see if the piece that has just moved is subject to capture. If so, we assume that the side about to move can escape both attacks. The attack with the highest points lost is ignored completely and the attack with the second highest points lost is moved up in its place, Current Limitations and Future Developments The problem of the Knight fork as just discussed is only one of a whole set of diffi- culties. Pinned pieces, the overworked piece, discovered attacks and other motifs can all occur dynamically during play of a board position, but are difficult to evaluate stati- cally. Attacks of this nature are second order attacks and are not considered in the ex- change evaluator we described. There are eight possible second order attacks (see table 4). The first group are the discovered attacks and the second group are the trans- parent attacks. If all of the second order attacks could be taken into account, the evaluation would be much improved. Cur- rently work is being done to accomplish this. Ultimately, of course, the entire board should be considered as a single complex battle. How close to this ideal can static evaluation progress? At what point does static evaluation begin to take more time than the look-ahead itself? Where will com- promises in the evaluation be least harmful? Currently in the field of computer chess there is a tendency to downplay the impor- tance of look-ahead in future developments. Has look-ahead reached a dead end? Will it be replaced by a Sargon-like exchange analysis? These are open questions.# Group Type Description ——s Wt > B1 w2 W1 attacks B1. If B1 moves, W1 defends W2. wi w2 w3 W1 defends W2. If W2 moves, W1 defends W3. Discovered << Attacks wi 61 ez Wi attacks BY. If 81 moves, W1 attacks 82, (PIN: wi w2 "Bt W1 defends W2. If W2 moves, W1 attacks B1. wi B1 > W2 W1 attacks B1. B1 attacks W2. W1 defends W2 through Bi. wi > w2 wa Wi defends W2. W2 defends W3. W1 defends Transparencies W3 through W2. Wi — B1 + B2 W1 attacks B1. B1 defends B2. W1 attacks B2 through B1. (PIN) wi > w2 > Bt W1 defends W2. W2 attacks B1. W1 attacks B1 through W2. 28 November 1978 © BYTE Publications Inc More and more, you see the North Star HORIZON computer at work: in busi- ness, research, and education. Its high performance qualifies the HORIZON for demanding professional applica- tions. Over 10,000 users during the past two years have proven that North Star hardware has the reliability for day-in, day-out computing. The HORIZON is now a serious candidate for any small system installation. SOFTWARE IS THE KEY TO HORIZON MATURITY North Star BASIC and DOS have been used to develop hundreds of com- mercial program packages. These packages establish that North Star software has the completeness and convenience necessary for serious program development. Because of the many independent vendors offering software using North Star BASIC and DOS, the HORIZON owner now has the widest selection of software in the microcomputer industry! Software available includes: word processing, general ledger, accounts payable/ receivable, mailing list processing, inventory and income tax prepar- ation. Program development systems such as assemblers, debuggers, editors, PILOT and FORTRAN are also available. EXPAND YOUR HORIZON The basic HORIZON computer in- cludes a Z80 microprocessor, 16K bytes of RAM memory, an I/O interface and one Shugart minifloppy disk drive. The HORIZON can be expanded to 60K bytes or more of RAM, three disk drives, and three 1/O inter- faces. Performance can be enhanced by the addition of the North Star hardware floating point board. Also, S-100 bus pro- ducts from other manufacturers may be used to expand the HORIZON. For more informa- tion, contact your local computer store. NoatH *® Star Computers 2547 Ninth Street Berkeley, California 94710 (415) 549-0858 Circle 285 on inquiry card. BYTE November 1978 29 i} a a Considering a Microcomputer? Be Sure to Check Out the Product Offerings of the World’s Largest Full Line Microcomputer Company. All Ohio Scientific machines come with microcomputing’s fastest full feature BASIC-in-ROM or on-Disk for instant use. Challenger | Sarie configuration Economical computer systems that talk in BASIC. Ideal for hobbyists, students, education and the home. Superboard II — World's first complete system on aboard 4K RAM including keyboard, video display, audio cassette, BASIC-in-ROM and up to 8K RAM Challenger IP — Fully packaged Superboard !! with 4K RAM power supply Challenger IP Disk — Complete mini-floppy system 16K RAM expandable to 32K RAM. Challenger |IP Sarie Ultra high performance BUS oriented microcomputers for personal, educational, research and small business use. (C2-4P — The professional portable 4K RAM C2-8P — The world’s most expandable personal machine 4K RAM for business or research applications C2-4P Disk — The ultimate portable 16K RAM C2-8P Single Disk — Ideal for education, advanced 16K RAM personal users, etc. C2-8P Dual Disk — Most cost effective small 32K RAM business system Challencer -. inter Same great features as Challenger IiP Series for those who have serial terminals: small business, education, industry. C2-0—Great starter for users with a terminal 4K RAM C2-1 — Great timeshare user accessory; cuts costs 4K RAM by running simple BASIC programs locally C2-8S — Highly expandable serial machine, can 4K RAM add disks, etc hallanger |!) Th i ‘pul The unique three processor system for demanding business, education, research and industrial development applications. C3-S1 — World's most popular 8” floppy based 32K RAM microcomputer dual floppys C3-OEM — Single package high volume user version 32K RAM of C3-S1 dual floppys C3-A — Rack mounted multi-user business system 48K RAM directly expandabe to C3-B dual floppys C3-B — 74 million byte Winchester disk based system. 48K RAM World's most powerful microcomputer dual floppys OHIO SCIENTIFIC also offers you the broadest line of expansion accessories and the largest selection of affordable software! Compare the closest Ohio Scientific Model to any other unit you are con- sidering. Compare the performance, real expansion ability, software and price, and you will see why we have become the world’s largest full line microcomputer company. ')'m interested in OSI Computers. Send me information on: 'D Personal Computers 1 Educational Systems 1D I'm enclosing $1.00 for your 64-page small computer buyer’s guide. t 1 ' OIRO SSIENTIFC | I I [ Ohio residents add 4% tax 1 Name | Address icity 'state 30 BYTE November 1978 O Small Business Computers C Industrial Development Systems Base Price $ 279 $ 349 $1190 $ 598 $ 799 $1464 $1738 $2597 $ 298 $ 498 $ 545 $3590 $3590 $5090 $11,090 1333 S. Chillicothe Road Aurora, Ohio 44202 (216) 562-3101 Seas feo: : if i Hl ! iH fi Circle 290 on inquiry card. The Age of Affordable Personal Computing Has Ohio Scientific has made a major breakthrough in small com- puter technology which dramatically reduces the cost of per- sonal computers. By use of custom LSI micro circuits, we have managed to put a complete ultra high performance computer and all necessary interfaces, including the keyboard and power supply, on a single printed circuit board. This new computer actually has more features and higher performance than some home or persona! computers that are selling today for up to $2000 It is more powerful than computer systems which cost over $20,000 in the early 1970's. This new machine can entertain your whole family with spec- tacular video games and cartoons, made possible by its ultra high resolution graphics and super fast BASIC. It can help you with your personal finances and budget planning, made possible by its decimal arithmetic ability and cassette data storage capa- bilities. It can assist you in school or industry as an ultra powerful scientific calculator, made possible by its advanced scientific Baye 0 1 Challenger 1P $349 Fully packaged with power supply. Just plug in a video monitor or TV through an RF con- verter to be up and running. Superboard II $279 For electronic buffs Fully assembled and tested. Re- quires +5V. at 3 Amps and a video monitor or TV with RF converter to be up and running. —Standard Features. Uses the ultra powerful 6502 microprocessor 8K Microsoft BASIC-in-ROM Full feature BASIC runs faster than currently available personal camputers and all 8080-based business com- puters 4K static RAM on board expandable to 8K Full 53-key keyboard with upper/lower case and user programmability Kansas City standard audio cassette interface for high reliability Full machine code monitor and I/O utilities in ROM Direct access video display has 1K of dedicated memory (besides 4K user memory), features upper case, lower case, graphics and gaming characters for an effective screen resolution of up to 256 by 256 points. Normal TV's with overscan display about 24 rows of 24 characters, without overscan up to 30 X 30 characters. Extras ® Available expander board features 24K static RAM (addi- tional), dual mini-floppy interface. port adapter for printer and modem and an OSI 48 line expansion interface. . Assembler/editor and extended machine code monitor available. interested in a bigger system? Ohio Scientific offers 15 other models of microcomputer systems ranging from single board units to 74 million byte hard disk systems. Circle 290 on inquiry card. Finally Arrived. math functions and built-in ‘timmediate'’ mode which allows complex problem solving without programming! This computer can actually entertain your children while it educates them in topics ranging from naming the Presidents of the United States to tutoring trigonometry all possible by its fast extended BASIC, graphics and data storage ability. The machine can be economically expanded to assist in your business, remotely control your home, communicate with other computers and perform many other tasks via the broadest line of expansion accessories in the microcomputer industry. This machine is super easy to use because it communicates naturally in BASIC, an English-like programming language. So you can easily instruct it or program it to do whatever you want, but you don't have to. You don’t because it comes with a com- plete software library on cassette including programs for each application stated above. Ohio Scientific also offers you hundreds of inexpensive programs on ready-to-run cassettes, Program it yourself or just enjoy it; the choice is yours. Ohio Scientific offers you this remarkable new computer two ways. 7) 01s | Nr cer amend Order direct or from your local Ohio Scientific dealer. 1 I'm interested. Send me information on your 7 Personal Computers [) Business Systems Send me a Superboard I! $279 enclosed 2 Send me a Challenger 1P $349 enclosed Include 4 more K of RAM (8K Total) $69 more enclosed Name - Address = ¢ | | ee {| » Seana Payment by: BAC (VISA) MasterCharge ___MoneyOrder ___ Credit Card Account # Expires __ Interbank #Master Charge) — (Ohio Residents add 4% Sales Tax TOTALCHARGEDORENCLOSED ____ All orders shipped insured UPS unless otherwise requested FOB Aurora, OH America's Largest Full Line Microcomputer Company 1333 S. Chillicothe Road © Aurora, Ohio 44202 (216) 562-3101 BYTE November 1978 31 The C3-S] by Ohio Scientific Possibly the world’s most popular floppy disk based microcomputer. Since its introduction in August, 1977, the Challenger I!l has gained tremendous acceptance in small business, educational and industrial development applications. Thousands of C3-S1's have been delivered and today hundreds of C3-S1 demonstrator units are set up at computer retailers around the country. Why has the Challenger III become so successful in the fiercely competitive microcomputer industry? Here are just a few of the possible reasons. The Challenger III is the fastest microcomputer in BASIC (see ‘BASIC Timing Comparisons," Kilobaud, October, 1977, where Ohio Scientific out benchmarks all competitors). The Challenger Ili is the only computer system with a 6502A, 6800 and Z-80 offering the programmer all popular micros for maximum versatility. The C3 is backed by the largest base of systems level software for any microcomputer system including: For the 6502A: Microsoft 6 and 9 Digit BASIC Assembler Editor Word Processor OS-65D Development DOS OS-65U End User DOS with Extended BASIC For Floppys Winchester Hard Disks Muiti-users (Level 2) Distributed Processing (Level 3) For the 6800: Floppy DOS Assembler Editor For the Z-80: Floppy DOS Microsoft Disk Extended BASIC Microsoft FORTRAN Microsoft COBOL Macro Assembler and Editor And Much More The C3 supports OS-65U, the ultra high performance “virtual data memory" DOS for floppys and hard disks which makes complex file structures like multi-key ISAM easy to use. @ The C3 is backed by a large library of applications programs 32 BYTE November 1978 | CHALLENGER III and can make use of the tremendous amount of BASIC programs offered by independent suppliers and publishers because it uses Microsoft BASIC, the standard of the industry. Complete turnkey and custom business packages are available for the C3 from most OHIO SCIENTIFIC DEALERS. The C3 electronics and software are available in alternate mechanical configurations for special applications including the C3-OEM for volume users and the C3 letter series (C3-A, C3-B) which are optimized for use with hard disks. C3 systems are always delivered ready to use with 32K static RAM, dual floppys for 500K bytes of on-line storage and an RS-232 port strappable from 75 to 19,200 baud all standard in the minimum configuration. C3 systems offer the greatest expansion capability in the microcomputer industry. The C3 series supports OHIO SCIENTIFIC’S full line of over 40 expansion accessories. The maximum configuration is 768K bytes RAM, four 74 million byte Winchester hard disks (CD-74), 16 communications ports, real time clock, line printer, Word Processing printer and numerous control interfaces. C3 systems have phenomenal performance-to-cost ratios. The C3-S1 base price with 32K RAM, dual floppys, RS-232 port complete with 8K BASIC and DOS is under $3600 and expan- sion accessories are comparably priced. For example, the CD-74, 74 million byte Winchester disk complete with interface and OS-65U operating system at about $6000. The C3 series is quite possibly so successful because it offers the highest hardware performance, best software support, most versatility and greatest expandability in the micro- computer systems market at nearly the lowest price in the industry. For more information, contact your local OHIO SCIENTIFIC DEALER or the factory at (216) 562-3101. 1333 S. Chillicothe Road e Aurora, Ohio 44202 Circle 290 on inquiry card. The C3-B by Ohio Scientific STANDARD FEATURES: © 74 million byte Winchester tech- nology disk drive yields mainframe class file access speeds and capacity. » High level data file software makes high performance file struc- tures like multikey ISAM easy to use. \ Triple processor CPU with 6502A, 6800 and Z-80 gives the pro- grammer the best of all worlds in performance and versatility. » The included 6502A based ex- tended disk BASIC by Microsoft out-benchmarks every micro available, including 4 MHz Z-80 and LSI-11 with extended arithmetic. © 48K of high reliability static RAM is standard. © High density 8” floppys provide program and data mobility from machine to machine. » Completely integrated mechani- cal system with UL-recognized power supplies; continuous duty cycle cooling; modular construc- tion and rack slide mounted subassemblies. » Based on a 16 slot Bus-oriented architecture with only 7 slots used in the base machine. Directly expandable to 300 megabytes of disk, 768K of RAM in 16 partitions, 16 communication ports, plus console and three printers. » C3-B’s have been in production since February, 1978, and are available now on very reasonable delivery schedules. The C3-B was designed by Ohio Scientific as the state of art in Circle 290 on inquiry card. small business computing. The system places its power where it’s needed in the smal! business environment; in the data files. The C3-B’s advanced Winchester tech- nology disk, coupled with its smart controller and dedicated high speed memory channel, gives the C3-B data file performance com- parable with today’s most powerful maxi-computers. Yet, the C3-B costs only slightly more than many floppy only com- puters but offers at least a thou- sand times performance improve- ment over such machines (50 times storage capacity multiplied by 20 times access speed improvement). But what if your business client cannot justify starting with a C3-B? Then start with Ohio Scientific’s in- expensive C3-S1 floppy disk based system running OS-65U. When he is ready, add the CD-74 big disk and directly transfer programs and files from floppy to big disk with NO modifications. That’s upward expandability! *Rack as shown above complete with 74 megabyte disk, dual floppys, 48K of static RAM, OS-65U operating system and one CRT ter- minal under $13,000. Multiple terminal systems with printers and applications software are priced in the mid-20's. se SESS 1333 S. Chillicothe Road * Aurora, Ohio 44202 (216) 562-3101 BYTE November 1978 33 Functional Approximations Fred Ruckdeschel 773 John Glenn Blvd Webster NY 14580 Many BASIC interpreters presently in use have limited function calculation capability. Almost all interpreters larger than 4 K bytes have built-in routines for determining square roots, logarithms and exponentials, as well as some trigonometric functions like sine and cosine. Several interpreters also provide inverse trigonometric functions via the arctangent function. However, many minicomputer and micro- computer systems do not have such software. Also, some of the newer microprocessors presently do not have much support soft- ware, | have recently been developing soft- ware for use with the North Star Micro-Disk system; specifically, working with North Star BASIC, version 6, release 2. The North Star software contains sine and cosine func- tions but no inverse trigonometric routines. This deficiency led to a cursory investigation of series approximations which very quickly showed that Taylor series expansions are not generally optimum for computer use. Taylor Series Expansion In general, any real, continuous function f(x) having defined derivatives may be ex- pressed as a polynomial expansion about a reference point x, with the longhand representation: ‘O F(x) = fxg) + £) (xg) (x= XQ) + £0) (x6) (x Xp)? /2E +... (1a) Observe that fl") (x,) is defined to be the nth order derivative of f(x) evaluated at x equal to x,. The shorthand equivalent of equation (1a) is: f(x) = Sf) (xg) (xx 9) Mn! n=0 f(x) = lim fy, (x) (1b) noe falx) = D> £™) (x5) (x—x9)™/m! m=0 Equation (1b) is in a form which is con- venient in terms of BASIC’s FOR-NEXT loop evaluation, which may account for its popularity with computer programmers. Many programmers who are faced with approximating a function use a Taylor series expansion along with a convergence test such as: If,O) fy @)I<e (2) Presumably when the difference between the approximation using n terms and that using n- 1 terms is less than e, the accuracy of f,(x) in approximating f(x) is better than ¢. This assumption can be grossly in error depending on the function being evaluated. Slowly converging series often present problems in this respect The reasons for not indiscriminately using equations (1) or (2) may be demon- strated by considering the sine and arctan- gent functions. The Taylor series expansion around the zero reference point (known as the MacLaurin series) for the sine func- tion is: sin(x)=x 3/3! +x5/5!—... (3a) or: sin(x) =D (= 1)" x20*1)/(2n+1)h n=0 (3b) If we apply equation (2) as the test for accuracy, we have x (2n41) tome <& (4) If x is one radian (approximately 57°) and the required accuracy is 10-8, then equa- tion (4) indicates that seven terms are re- quired in the series for the specified ac- curacy. The test for residual may be done more correctly in principle by noting that the series is uniformly convergent, having terms alternating in sign. Thus the absolute error of the approximation is less than the absolute value of the last term included. Therefore we again conclude that seven terms are needed for 1078 accuracy in approximately calculating the sine of one radian. In the case of alternating series having terms which monotonically decrease in absolute value, equation (2) is applicable. If, instead, we are interested in the sine of —1, the accuracy test would again call for seven terms. However, this time, because the signs of the terms do not alternate, a ratio test would have to be applied to cor- rectly examine the residual, yielding the same result for the required number of terms. In general, if the series is rapidly converging, equation (2) is an adequate test for accuracy. So far we have assumed that the com- puter is perfect in terms of roundoff error. In some eight decimal place accuracy inter- preters and compilers, the computer rounds off to the eighth decimal place by consis- tently rounding down or up. Quite often the direction is down, since this corresponds to simple truncation. In those cases the en- suing error in calcul