Cromemeo [2] [!!] _/_ Fill your computer needs with the industry's most professional microcomputers

Model Z-2 ^Model Z-20

One or two disks System Two

Dual disk Up lo 512K of RAM/ROM Up to 512K of RAM/ROM

Up to 184K of disk Up to 512K of RAM/ROM Up to 184K of disk

Fill your computer needs with the industry's

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#1 IN RELIABILITY When you choose Cromemco you get not only the industry's finest m icrocomputers but also the indus­

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What's more, you get a computer from the manufacturer that compu­

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Your range of choice i ncludes our advanced System Three with up to four 8" d isk d rives. Or choose from the System Two and _Z-20 with 511 drives. Then for ROM-based work there's the Z2. Each of these com­

puters further offers up to V2 mega­

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We say these are the industry's most professional m icrocomputers because they have outstanding fea­

tures l ike these:

• Z-SOA microprocessor - oper­

ates at 250 nano second cycle time - nearly twice the speed of most others.

*Rated in The 1977 Computer Store Survey by Image Resources, Westlake Village, CA.

Circle ⁸⁰ on inquiry card.

Up to 512 kilobytes of RAM and 1 megabyte of disk storage

_/_ [!!] ^� [2]

lro: ^{o M � � o Q - • -· .., .. T • ... " • H .. • •} 1

System Three Two to four disks Up to 512K of RAM/ROM Up to 1 megabyte of disk

• 30-amp power supply- more than adequate for your most demanding application.

• 21 card slots to allow for un­

paralleled system expansion us­

i n g i n d u stry-standard S - 1 00 cards.

• S-100 bus- don't overlook how important this is. It has the in­

dustry's widest support and Cro­

memco has professionally imple­

mented it in a fu lly-shielded design.

Cromemeo

• Cromemco card support of more than a dozen circuit cards for process control, business sys­

tems, and data acquisition in­

cluding cards for A-D and D-A conversion, for interfacing daisy­

wheel or dot-matrix printers, even a card for programming P ROMs.

• The industry's most professional software s u p port, including COBOL, FORTRAN IV, 16K Disk­

Extended B A S I C, Z-80 Macro Assembl er, Cromemco M ulti­

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inets available.

FOR TODAY AND TOMORROW Cromemco computers will meet your needs now and in the future because of their unquestioned tech­

n ical lead ership, profess ionalism and enormous expandabi l ity.

See them today at your dealer.

There's no substitute for getting the best.

see next _page

r\ Ll'

280 BERNARDO AVE., MOUNTAIN VIEW, CA 94040 • (415) 964-7400

BYTE October 1978

-•.AliSOll COMPUTU lf S IA.IlCH CORP.

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1 51 1 52 1 54 1 66 1 93 222 224 224

In l;he Queue

Foreground

NO POWER FOR YOUR INTERFACES?: Build a 5 W DC to DC Converter Hardware-Ciarcia

A "TINY" PASCAL COM PI LEA, Part 2: The P-Compiler Pascal-Chung- Yuen

T ESTING M EMORY IN BASI C Software-Adams

FIRST STE PS IN COMPUTER CH ESS PROGRAM M ING Software Chess-the Spracklens

L I N E AR CIRCUIT ANA LYS IS Simulation-Anderson

SOLVING T H E E IG H T QUEENS PRO BL E M Software-Smith

A S I M P LER DIG I TA L CASSETTE TAPE INTERFACE Hardware-Burhans

SOUPING UP YOUR SwTPC 6800 Hardware-Hughes A NOV E L BAR CODE R EADER

Hardware-Fame//

A COMPUTER CH ESS TUTOR I A L Computer Chess-Whaland

Background

A M E MORY PATTERN SENSITIV ITY TEST Debugging-Kinzer

PAM/8: A New Approach to Front Panel Design Computer Design-Letwin

ASS E M B L ING T H E H9 V I D EO TERM INAL Product Description-Steeden CR E ATING A CH ESS P LAYER

Chess Tutorial-Frey-A tkin

Nucleus

In This BYTE

On Using a Persona l Computer for a Practical Purpose Letters

Book Reviews Technical Forum Programming Quickies BYTE's Bits

BYTE's Bugs Clubs, Newsletters Event Queue

Product Description: Micro-Scan Corp Bar Code Scanner What's New?

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Reader Service

BYTE is published monthly by BYTE Publications Inc, 70 Main St, Peterborough NH 03458. Address all mail except sub­

scriptions to above address: phone (603) 924-7217. Address all editorial correspondence to the editor at the above address.

Unacceptable manuscripts will be returned if accompanied by sufficient first class postage. Not responsible for lost manu­

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Printed in United States of America. Each separate contribution to this issue and the issue as a collective work copyright ©

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"' IJ�TI

PUBLISHERS Virgini1 Londoner Gordon R Willi1mson EDITOR IN CHIEF C1rl T Helmers Jr

VICE-PRESIDENT, PRODUCTION Judith H1vey

PRODUCTION MANAGER K1ren Gregory ADVERTISING DIRECTOR John H;ayes

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COMMUNICATIONS COORDINATOR J<�mes C Morrissett

SENIOR EDITOR Christopher P Morpn EDITORS R01ymond G A Cote Bl1ise W Liffick Rich01rd Shuford PRODUCTION EDITORS Nancy Salmon David William H.-.ywnd Peter Perin

PRODUCTION ASSISTANT Cheryl A Hurd PRODUCTION ART Stephen Kru5e W<�.i Chiu li Dorothy Shm1onsky Ellen Sh1monsky NEW PRODUCTS EDITOR CLUBS, NEWSLETTERS Laur1 A H1nson

ASSISTANT ADVERTISING DIRECTOR P1trici1 Clark

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Ann Gr1ves Pamela R Heaslip Agnes E Perry DEALER SALES Ginnie F Boudriuu Anne M &ldwin TRAFFIC MANAGER Rick Fuette RECEPTIONIST )Kqueline hrnsh�w DRAFTING T ech�rt Associ�tes DRAWING EDITOR Kent Rich,ud TYPOGRAPHY Goodw�y Gr�phics PHOTOGRAPHY Ed Cr�btree PRINTING

The George B;ant;a Comp;any ASSOCIATE EDITOR O;aniel Fylm;a ASSOCIATES W;alter B�nks Steve Ci;arci;a O;avid Fylstr�

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October 1978 ©BYTE Publications Inc 3

Robert Tinney's painting on the cover this m on th is a fanciful i m age of compu ter chess. A Knight floats above an ancient stone chessboard with the u biquitous fl oppy disk beneath. Four articles in this issue are devoted to the art of computer chess, including the first part of a 4 part series by the creators of Chess 4.6, the worl d championshi p chess pro­

gram.

In This

One cause of seemi ngly u nexplain­

able program errors may be incorrectly operating memory. A Memory Pattern Sensitivity Test discussed by Don Kinzer will help to determine if your memory is operating correctly.

page 7 2

If you need - 12 or +1 5 V for you r latest hardware design, and have only +5 Y, what can you do? Read No Power for Your I nterfaces? Build a

5 W · DC to DC Converter by Steve Ciarcia. Several i nexpensive, practical designs are descri bed, to give you everything from - 1 5 to +1 5 V from

a +5 V source. page 22

In Part 1 of A "Tiny " Pascal Com­

piler, in the Septem ber 1 978 BYTE, Kin-Man Chung and Herbert Yuen described the syntax of a Pascal su bset and described a hypothetical stac k machine, cal led a p-machlne. This month they describe a com piler that generates codes for the p-machi ne.

page 34

Would you l i ke a fast and easy way to test your new memory board?

Author Russell Adams shows you how in Testing Memory in BAS IC. A simple program loads the memory locations with alternati ng 1 s and Os to spot those bad bits. page 58

The H8 computer from Heath fea­

tures a novel fi rmware front panel monitor compri sed of both hardware and software elements. Gordon Let­

win, Heath software designer, de­

scribes the design philosophy and the features of the system i n PAM/8:

A New Approach to Front Panel

Design . ^{page 70}

The winning program at the Second West Coast Computer Faire's Micro­

computer Chess Tournament in March of 1 978 was Sargon, written in Z-80 assem bler language. Sargon's creators, Dan and Kathe Spracklen, describe the move generating portion of their pro­

gram in First Steps in Computer Chess

Programming. ^{page 86}

A computer al lows you to try out a variety of i deas with nothing more than a program to see if they wi ll work. One way to use this potential i s to model electrical circuits in software.

Leonard H Anderson describes how to perform Linear Circuit Analysis on you r computer. page 700

The eight Queens problem is a venerable puzzle in recreational mathe­

matics. Terry Smith descri bes his thought processes in working ou t a solu tion in his article, Solving the E ight Queens Problem. An occasional dose of cleverness is often the key to solving a difficu l t problem, as Terry

demonstrates. page 7 22

For someone who is looking for a good quality video terminal which is easy to work with and wil l be user serviceable, the Heath ki t H9 is the solution . Terry Steeden descri bes his pleasant experiences Assembling the H9 Video Terminal and havi ng it work correctly the first time. page 730

Digital recording of computer pro­

grams and data is an attractive alterna­

tive to standard audio cassette record­

i n g tech niques because of its rel iability.

and simpl icity. Ral ph Burhans de-

scri bes an updated version of earlier digital recording schemes i n A Simpler Digital Cassette Tape Interface.

page 742

If you own a SwTPC 6 800 com­

puter and want to increase the pro­

cessor clock speed with a m i n i m u m of fuss, read Souping Up Your SwTPC 6800 by Steve A Hughes. The article descri bes a simple circu i t that plugs directly i n to a soc ket on the 6 800 processor board. Changing the cloc k speed is then done b y simply plugging in a new crystal oscillator. page 744

Last year we ran a con test in which readers were asked to design their own PAP E R BYTEtm bar code readers and su bmit them to us. One of the winning entries, by Cam p be l l Farne l l and Glen Seeds, is descri bed in their article, A N ovel Bar Code Reader. page 762

For a short in troduction to the world of computer chess, read Norman Whal an d 's A Computer Chess Tutorial.

The basic principles of chess strategy and tactics are covered in d iscussions of game trees, alpha-beta pruning, m i n i m ax strategies and so on. page 768

Creating a Chess Player was written by two people at the forefront of re­

search in computer chess: David Frey, editor of Chess Skill in Man and Ma­

chine, and Larry Atkins, coau thor of Chess 4.6, the world champion chess program that recen tly beat a Grand­

master in a simu ltaneous exhibition.

The article discusses the thin king pro­

cesses in the chessplayer's m i n d and how such processes are transformed into a computer program. page 782

AC/

woJ cow,un! nmMs I ^mo

WE'RE ALTOS COMPUTER SYSTEMS. Our SUN-SERIES ACS8000 business/scientific computer creates a new standard in quality and reliability in high technology computers.

HIGH TECHNOLOGY The ACS8000 is a single board, BUILT-IN RELIABILITY The ACS8000 is a true single Z80® * disk-based computer. It utilizes the ultra-reliable board computer. This makes it inherently reliable and main- Shugart family of 8 inch, IBM compatible, disk drives. A tainable. The board and the two Shugart drives are easily ac-

choice of drives is available: single or double density, single or cessible and can be removed in less than five minutes. All elec- double sided. Select the disk capacity you need, when you tronics are socketed for quick replacement. Altos provides need it: ¥2M, 1M, 2M, or 4M bytes. The ACS8000 features complete diagnostic utility software for drives and memory.

the ultimate in high technology hardware: a fast 4 MHz Z80 CPU, 64 kilobytes of 16K dynamic RAM, 1 kilobyte of 2708 EPROM, an AMD 9511 floating point processor, a Western Digital floppy disk controller, a Z80 direct memory access, Z80 Parallel and Serial I/0 (two serial RS232 ports, 1 parallel port), and a Z80 CTC Programmable Counter/Timer (real time clock). In essence, the best in integrated circuit technology.

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QUALITY SOFTWARE Unlimited versatility. The ACS

8000 supports the widely accepted CP/M®** ^{disk operating}

system and FOUR high level languages: BASIC, COBOL,

PASCAL and FORTRAN IV. All available NOW.

PRICE $3,840. Standard ACS8000 system with 32 Kb RAM and Y2 Mb disk. FPP, DMA and software optional. Dealer/OEM discounts available. Delivery: 3 weeks ARO.

•zso is a tr::tdcmark of Zilog. Inc .

.. CP/M is a trademark of Digital Research. Inc.

Dealer /rep inquiries invited.

Circle 7 on i nquiry card .

COMPU;-rER SYSlTEMS

On Using a Personal Computer for a Practical Purpose

by Carl Helmers

Finally, it had to happen to me. We all know that personal computers are supposed to be a cross between a necessity and a luxury. But the critics tend to harp on our tendency to get carried away by the fun and to ignore the practical uses of our wonderful servants. As if to answer that justified criticism, I finally came up with a genuine practical use for a small computer in the monthly operations of BYTE's editorial office. Now this prac�ical application is by no means the kind of automated editing

Rank Topic

1 Applications to everyday life

2 Household automation with computers 3 Personal data base design and implementation 4 Applications to personal business

5 Voice recognition by computers 6 The art of p rogramming

and type preparation facility I would like to have some day if and when I ever become rich and famous. But this is a genuine, once a month, cyclically run application program.

At BYTE, we have so far purchased two Apple II computers (among others) for use in educating our employees, and in order to have some facilities around the office.

One of these Apple II computers sits in my office, and at the time of this exercise Continued on page 147

Total Standard Deviations Weighted Count Away from Mean

1 2888 2.1 78

1 2886 2. 1 77

1 09 1 1 1 .1 79

1 0683 1 .064

1 0654 1 .049

1 0552 .997

7 Logical games (require much thinking, no dexterity) 1 0277 .858

8 Voice synthesis with computers 1 001 4 .725

9 The art of hardware design 9875 .655

1 0 Computer control of mechanisms 9832 .633

1 1 G raphics software design 9707 .570

1 2 A rtificial intel ligence: general interest in AI 9523 .477

1 3 Action games (require much thinking, no dexterity) 9465 .448

1 4 Educational uses of computers 9439 .435

1 5 Computer system design 931 1 .370

1 6 Text editing and processing 9233 .330

1 7 Graphics hardware design 8876 .150

1 8 Applications of computers to engineering 8766 .092

1 9 Experimentation with designs 8723 .073

20 General robotics: whole systems 8642 .032

2 1 Applications o f computers t o physical science 8593 0.

22 Chess and computers 8553 -.01 3

23 Computer communications networks 8424 -.079

24 Simulations of real or mythical situations 831 5 - . 1 34

25 A I : pattern recognition 8221 -.1 81

26 Design of information structures 8 1 1 1 -.237

27 Use of graphic displays for a rtistic purposes 7556 -.51 7

28 Mathematical analysis and algorithm design 7551 -.520

29 Language design 7534 -.529

30 Compiler or interpreter design 7273 -.669

31 AI: representations of knowledge 6982 -.848

32 A I : Natural language parsing 6531 -1 .035

33 Computers used for musical purpose:

real time performance 6477 - 1 .062

34 Applications of computers to biological sciences 5785 - 1 .41 2

35 Amateur radio and computers 5369 - 1 .623

36 Computers and music: stochastic composition 51 38 -1 .739

37 Application of computers to social sciences 4745 - 1 .938

38 A I: theorem proving 4686 - 1 .968

: �

t'

t?,

Table 7 : Respondents were asked to assign a numerical preference from 0 (no interest) ^{to 7 0}

��

(highest interest) for each of these 38 categories. The column labelled total weighted count con­

tains the sum of counts in each possible response (1 to 7 0) multiplied by the response itself.

Thus if a count of 29 were found in the interest weight ₇ for some category, the contribution to the weighted sum would be ₇ x 29 = 203. The standard deviation and mean were calculated for the data, and the deviation from the mean was expressed in the rightmost column in units of one standard deviation for each category. These data were "output" to a typewriter from the _I•

screen of the Apple II using a manual process, then typeset in the usual method.

North Star Systems Go To Work

I'J •I 5"•\f * C,

,.mr•,

HORIZON

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 S t a r h a r d w a r e h a s the r e l iabil ity 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 BAS I C and DOS have been u sed to develop hundreds of com­

m ercial 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 m icroco m puter i nd ustry! S oftware available i ncludes: word processing, g eneral ledg er, accou nts payable/

receivab le, m a i ling list processi n g , i nv e ntory and i ncome t a x prep ar­

ation. Program development systems s u ch as a s s e m b l e r s , d e b u g g e rs, editors, P I LOT and FORTRAN are also available.

EXPAND YOUR HORIZON

The basic H OR IZON com puter i n­

cludes a Z80 microprocessor, 16K bytes of RAM memory, an 1/0 interface and one Shugart minifloppy disk drive.

The H ORIZON can be expanded to 60K bytes or more of RAM , three disk drives, and three 1/0 inter­

faces. Performance can be enhanced by the addition of the North Star hardware floating point board.

Also, S-1 00 bus pro­

d u c ts f r o m o t h e r manufacturers may be used to expand the H ORIZON.

For more informa­

tio n , co nt act yo u r local computer store.

NoRTH* STAR CoMPUTERS

2547 Ni nth Street

Berkeley, California 94710 (415) 549-0858

Circle 28 5 on i n q u i ry card. BYTE

October

Sol:

The small computer thatwon't

fence you in.

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 .

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 N 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.

Processor Technology

BYTE Occober 1978 9

See Sol®.

at all these fine

computer centers

AL: Birmingham: ICP Computerland,

(205) 979-0707. CA: 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) 457-9311. 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. GA: Atlanta:

Atlanta Computer Mart, (404) 455-0647. IL:

Lombard: Midwest Microcomputer. (312) 495-9889. lA: Davenport: Computer Store of Davenport. (319) 386-3330. KY: Louisville:

Martronix Associates. (502) 459-0500. MD:

Towson. Computers Etc .. (301) 296-0520.

MN: Minneapolis: Computer Depot. (612) 927-5601. MO: Florissant: Computer Country, (314) 921-4434. NH: Nashua:

Computerland of Nashua, (603) 887-5238. 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. Rl: Warwick:

Computer Power. Inc .. (401) 738-44 77.

SC: Columbia: Byte Shop, (803) 771-7824. TN:

Kingsport: Microproducts & Systems, (615) 245-8081. TX: Arlington: Computer Port, (817) 469-1502. Arlington: Micro Store . (817) 461-6081. Houston· Interactive Computers, (713) 772-5257. Houston: Interactive Computers.

(713) 486-0291. Lubbock: Neighborhood Computer Store, (806) 797-1468. Richardson.

Micro Store. (214) 231-1096. UT: Salt Lake City: Home Computer Store, (801 )484-6502 VA: Mclean: The Computer Systems Store.

(703) 821-8333. WA: Bellevue: Byte Shop

Computer Store. (206) 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) 445-4280. 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. 93-1988 or 57-7177. AUSTRALIA:

Sydney· Automation Statham Ply. ltd., 47 Birch St.. (02) 709.4144. Carnegie: Sontron Instruments, 17 Arawatta St., (03) 569.7867.

BELGIUM: Bruxelles: S. P.R. L. Finncontact, Square Larousse, 5, 2/345-98-95. COLOMBIA:

Bogota: Video National, Diagonal 34N 5-62, 326650. GREECE: Athens: Attikos, lnc . .41 Char.

Tricoupi T.T. 145, 3604091. JAPAN: Tokyo:

Japan Personal Computers, Ltd .. Yamamoto Bldg.

No. 11-18. (03) 375-5078.5079. MEXICO:

Plateros: lndustrias Digitales, S.A. de C.V .. (905) 524-5132. PHILIPPINES: San Juan:

Integrated Computer Systems. Inc .. Suite 118, L1 M KET KAI Bldg .. Ortigas Ave. SWEDEN:

Stockholm: Werner Elektronix. Torsvagen 61, Box 72, (0) 8 717-62-88. UNITED KINGDOM:

Huntingdon. England: Comart, ltd, 24A Market Square, St. Neots. Cambridgeshire, (0480) 74356. VENEZUELA: Los Ruices. Caracas:

Componentes Y Circuit as Electronicos.

TILCA 355591.

Processor uogy

TOP-DOWN MO D U LA R P ROG RAM M I N G

enjoyed the article, "Top-Down M o d u l ar Progra m m ing," by A l bert D Hearn i n july 1 9 7 8 B YTE, page 3 2 ; I thought he d i d a good job of ex plaining the s u bject. W h i le I realize that he was p u rposely try i n g to simplify m atters,

I do take excep tion to his com m e n t that a m o d u le should be no more than 5 0 l i n es l ong.

The concepts of structu red pro­

gramming are i n tended as guidel i nes, not as the dogma for a program mer's religio n . All of the better known pro­

ponen ts of the methodology stress this point, along w i th the idea that you m ust ap proach the study of structured pro­

gra m m i n g w i th your eyes open, making y o u r own evaluation. In this l igh t let u s explore the 5 0 l i ne l imit.

One of the bases for breaking a program u p i n to modules is so that a com plex problem can be handled with small, easy-to-understand pieces of code.

One of the though ts about module size is, the refore, that a module ought to be able to fit on the pri n te d page. This is so that all the i n formation about the m o d u le is i n one p l ace and the pro­

gra m m e r doesn't have to t h u m b thro ugh several pages to read the code for a s i ngle m o d u le. (Having experienced "modules"

r u n n i n g as l ong_ as 1 0 to 1 5 pages, I

heartil y agree w i th this p h i l osophy .) In professional programming i nstal­

lations this idea h as frequently been translated i n to a local standard of about 50 l ines of code, since this is the n u m be r o f l ines w h i ch are printe d on an _sy, by 1 1 i nch (21 .25 by 27.5 em) page com ing o u t of a l i ne printer (allowing for headers , footers, e tc). For the personal com p u te r e n th usiast, howeve r, this l i m i t m ig h t b e m o re conveniently set at 2 4 , 3 2 or 40 l i nes - t h e size of the video d isplay.

For many more comp lex problems, i t is possible that a sign ificant m od u l e cannot be constructed in 2 4 l i nes. T h i s i s n o p roblem - just m ake t h e m o d u les longer. The poi n t is to try to restrict the m o d u l e size to a length which en­

h ances the· p rogram me r's abil ity to u nde rsta n d the code.

Th e basics of structured p rogram­

m i ng m ust be stud ied, eval uated, and possibly modified to work in each in dividual situ ation. There are a l o t of great ideas i n c l u d e d in the struc tu re d progra m m i n g lore, b u t t h e y should n o t b e adopted b l i n d ly .

Jim Flem ing 2220 Sims Dr Col umbus I N 47201

Continued on page 156

56 GREAT LOCAT IONS

ComputerLand®

A LABAMA Huntsvi l l e CAL I FORNIA

Dublin El Cerrito Hayward Los Altos Los Angeles Mission V i ej^o San Bernardino San Diego San Francisco San Jose San Mateo Santa Rosa Thousand Oaks Lawndale Tustin Walnut Creek COLOR ADO

Colorado Springs Denver

CONNECTICUT Fairfield DELAWA R E

Newark FLOR I D A

Boca Raton Ft. Lauderdale GEO R G I A

Atl anta HAW A I I

Honol u l u I L LINO I S

Arlington Heights Downers Grove Niles Oak Lawn Peoria I N D I ANA

Ft. Wayne KENTUCKY

Lou isvil l e MAR YLAND

Rockville M I CH I GAN

Grand Rapids Detroit MINNESOTA

Bloom in gton NEW HAMPSH I R E

Nashua NEW JERSEY

Cherry Hill Bergan County Morristown NEW YO RK

Buffalo I thaca NO. CAR O LINA

Charl otte OHIO

Cleveland OREGON

Portland PENNSYLVANIA

Harrisburg TEXAS

Austin Dallas Houston WASHINGTON

Bellevue Federal Way Tacoma

WASHINGTON, D.C.

W I SCONSIN Madi son INTERNATIONAL

(205) 539-1200

(415) 828-8090 (415) 233-5010 (41 5) 538-8080 (415) 94 1 -8 1 54 (2 1 3) 776-8080 (7 1 4) 7 7 0-0131 (714) 886-6838 (71 4) 560-9 9 1 2 (415) 546-1 592 (408) 253-8080 (415) 5 72-8080 (707) 528-1 775 (805) 495-3554 (213) 3 7 1 -7 1 44 (714) 544-0542 (415) 935-8502

Call D irectory Assistance (303) 7 59-4685 (203) 374-2227 (302) 738-9656

Call D i rectory Assistance Call Di rectory Assistance (404) 953-0406 Call Directory Assistance

(312) 255-8488 (3 1 2) 560-Q1 93 (312) 967-1714 (3 1 2) 422-8080 Call Directory Assistance Cal l Directory Assistance (502) 425-8308 (301) 948-7676

(6 1 6) 942-293 1 (313) 356-811 1 (6 1 2) 884- 1 4 74 (603) 889-5238

(609) 795-5900 (20 1) 845-9303 (201 ) 539-4077

(716) 836-6511 (607) 277-4888 (704) 536-8500 (216) 46 1 -1200 (503) 620-8170 (717) 736-11 1 6

(512) 452-5701 Call Directory Assistance ( 7 1 3) 9 77.0909

(206) 746-2070 (206) 838-9363 (206) 581-0388 Call Di rectory Assistance (608) 273-2020 Sydney, NSW Australia 29-3753 Winnipeg, Canada Call Directory Assistance

YIIIIY

I: II

If the truth is that you wont a computer ... then we wont to be your computer store.

We're Computerlond, the #1 computer store chain in the U.S. What"s meaningful about that fact is, that Computerlond 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 Computerlond store.

You'll find a product line that's continually evaluated to provide you with the widest and best selection in quality, brand nome microcomputers anywhere.

You'll find on 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 con get a firsthand experience of running a computer yourself.

CIIPmRS FIR BUSIIIESS

You'll find educational materials to give you a total insight into the world of microcomputers.

You'll find a fully equipped service deportment 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 con shore 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 ore already being used.

In business, the advent of the versatile and compact microcomputer has put the benefits of computing within reach of small companies. With systems starting at less than $6000, the businessman con

CIIPITERS FIR THE HIIE

I

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 con 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 ore in engineering development, process control, and scientific and analytical work.

Users of microcomputers in industry hove found them to be reliable, cost­

effective. tools which provide computing capability to many who would otherwise hove to wait for time on a big computer, or work with no computer at all.

And now we come to you, which leads us right bock 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 Computerlond 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 October 1978 11