Inventing the Atari 2600

The typical “Heavy Sixer” model of the Atari Video Computer Gadget (VCS) used to be launched in 1977. Therefore renamed the Atari 2600, it used to be the most well-most well-liked home sport machine of its period.

In slack 1975, sales of gadgets that made it seemingly for shoppers to play Pong on home tv sets had been booming. At Atari Inc., which had first launched Pong as an arcade sport and had manufactured one of the vital well-most well-liked home variations of Pong, engineers began seeking to search out the next arcade sport to build in consumer hands, ready for that folk would grow drained of two paddles and a ball.

They noticed Jet Fighter and Tank, however as a change of designing a custom chip for every sport, as used to be performed for Pong, they deliberate a machine that can maybe well play both games, four-participant Pong if somebody used to be involved, and seemingly just a few rather a lot of, as but unknown games. The machine used to be to be basically based mostly on a microprocessor.

In just a few months, Atari’s designers in Grass Valley, Calif., had made a working prototype, and over the next year, designers from Grass Valley and from Sunnyvale, Calif., refined what used to be to be the Atari Video Computer Gadget (VCS). It used to be launched in 1977, and six years later ranks as one of the vital successful microprocessor-basically based mostly merchandise ever constructed, with over 12 million supplied at about $140 apiece.

Success did now not attain with out complications. Production complications within the principle two years brought on Atari losses estimated near $25 million. But as soon as these complications had been solved and ample tool used to be developed, the VCS took off.

This article used to be first published as “Possess case historical previous: the Atari Video Computer Gadget” within the March 1983 area of IEEE Spectrum. A PDF model of the unique article including photos and technical diagrams is on hand on IEEE Xplore.

It’s well-liked today, now not due to it does an admirable job of taking part in Jet Fighter and Tank, however due to its versatile fabricate furthermore permits it to play chess and baseball, as effectively as Location Invaders, Pac-Man and rather a lot of the rather a lot of arcade games that had been invented for the reason that VCS got right here available on the market. Greater than 200 rather a lot of sport cartridges—the read-easiest recollections (ROMs) containing VCS tool—are now available on the market, manufactured by about 40 companies, and original games are constantly being developed. An estimated 120 million cartridges had been supplied at costs from $12 to $35, and the demand is such that, besides to seeking to search out extra 6502 microcomputers than somebody else within the field, Atari’s purchases of ROMs for its rather a lot of divisions is greater than that of all rather a lot of companies within the field mixed.

Atari and rather a lot of video-sport companies had been making microprocessor-basically based mostly arcade games for some time sooner than the VCS used to be developed, however the price of then-on hand processors—$100 or extra every—made the concept that of a dwelling consumer product basically based mostly on a microprocessor impractical. Then got right here Chuck Peddle and the 6502.

Mr. Peddle, who had left Motorola for MOS Abilities after designing the MC6800 microprocessor, seemed at Wescon—the annual West Fly electronics tag—in September 1975, offering to promote his original microprocessor by the barrel at $8 apiece. “Finally, no one knew that he easiest had one barrel to his title,” remembers Steve Mayer, cofounder of Cyan Engineering, Atari’s deepest consulting company in Grass Valley, and now senior vice president for R&D at Atari.

Mr. Mayer and Ron Milner, his colleague at Cyan, went to see Mr. Peddle at Wescon and stumbled on that the 6502 matched precisely the minimum specifications that that they had laid out some time sooner than in a blue-sky fabricate for a programmable video sport. The three went into the abet of the MOS Abilities suite, Mr. Mayer remembers, and in an hour the deal used to be struck. It began a revolution in home video games.

Looking out out for to Dwell on

No person noticed it that means at the time. “We had been actual seeking to live to converse the tale,” Mr. Mayer suggested Spectrum. Atari had entered the dwelling video market with a one-chip model of its Pong arcade sport, and it used to be constructing rather a lot of home video games, however every used to be basically based mostly on a single custom chip that took a year or extra and over $100,000 to invent—by the time an arcade sport reached the dwelling market, shoppers would maintain forgotten about it. A programmable home video sport gave the impact a clear different.

The critical to the fabricate used to be simplicity: making the tool cease as critical of the work as seemingly, so as that the hardware will be more reasonably priced—silicon used to be very expensive in these days. The microprocessor used to be synchronized to the tv scan rate and created the tag one or two traces at a time. This synchronization reduces memory requirements for the tv interface severely, however the processor have to constantly update the registers within the interface to salvage any tag at all. This system that feeds info to the video chip (called Stella, after its vogue designer’s bicycle) is identified as a kernel.

To additional decrease memory requirements, Mr. Mayer and Mr. Milner determined to tag the background of the veil at somewhat low decision, while displaying involving objects with better decision—low-decision playfield, excessive-decision avid gamers. They furthermore eliminated any provision for vertical synchronization and gave that task to the programmer. A VCS kernel have to depend the different of traces displayed on the tv veil and have to enact displaying a single frame in precisely the identical time—15.24 milliseconds—that it takes the TV assign’s electron gun to fabricate a single high-to-bottom sweep.

The critical to the fabricate used to be simplicity: making the tool cease as critical of the work as seemingly, so as that the hardware will be more reasonably priced.

Two prototypes of the Stella had been constructed: a purposeful prototype constructed by Mr. Milner to test the concept that, and a gate-stage prototype constructed by Joe Decuir, who used to be employed by Cyan in slack 1975. The gate-stage prototype used to be designed to mimic as carefully as seemingly the supposed closing chip, using circuit-fabricate tactics particular to MOS constructed-in circuits.

One severe MOS-dependent characteristic used to be using a particular counter—called a polynomial counter, or pseudorandom shift register—as a change of a real binary counter to resolve object positions on the veil. A polynomial counter occupies one-fourth the silicon dwelling of an the same binary counter, however, now not like a binary counter, it does now not depend in any easy converse. Thus, a programmer cannot calculate a veil assign for an object and cargo it into the assign counter.

The typical Stella prototype had easiest one signal to the assign counter: a reset that can maybe well trigger the instantaneous tag of an object. Mr. Decuir and Jay Miner, who designed the manufacturing model of the Stella chip, used this identical concept in their fabricate. In consequence, displaying an object in a given assign on the veil requires that the programmer depend the different of clock cycles taken by a given assign of instructions, determine how a ways across the veil the electron beam would be after the instructions had been carried out, and act accordingly. Once the assign counter for an object is reset at the ethical point, it continues to tag the thing at that space on succeeding traces.

To circulate objects, the prototype blocked out four clock pulses from the assign counters all the map thru the vertical blanking interval; a programmer might maybe well well then add pulses to circulate an object left or ethical—four pulses needed to be added to succor the thing within the identical assign. Mr. Miner added a assign of lunge registers, which add or subtract pulses robotically when a signal—called H-circulate—is distributed by the microprocessor. The H-circulate would be sent all the map thru the vertical blanking interval, or all the map thru the horizontal blanking interval within the starting assign of every line.

“This gave the impact innocuous ample,” acknowledged Larry Kaplan, the principle tool vogue designer employed to invent games for the Stella mission. “But I stumbled on early that it used to be seemingly to reposition participant objects all the map thru a veil [a frame of the TV picture], though that used to be now not a consideration of the fabricate.”

Circuit diagram drawn in pencil labeled Atari Microprocessor Game System, stamped Confidential, signed Decure 8 November 1976

Joe Decuir drew this circuit draw of what used to be to develop into the Atari Video Computer Gadget on 8 November 1976.

Joe Decuir

So Mr. Kaplan designed Air-Sea Conflict, which has horizontal bands of participant objects, a skill utilized in infinite VCS games, including Location Invaders, Freeway, Asteroids, and Football. “Without that single strobe, H-circulate, the VCS would maintain died a transient loss of life five years within the past,” acknowledged Mr. Kaplan, now vice president of product pattern at Atari.

H-circulate and a characteristic that allowed two or three copies of an object to be placed on the veil let one more VCS programmer, Rick Mauer, fabricate a dwelling model of the arcade hit, Location Invaders. That sport hit the arcades in 1979, when the VCS used to be going downhill after shedding money in 1977 and 1978.

“The VCS used to be now not doing that effectively—there had been easiest just a few million within the realm, and it looked admire it used to be dying—then Location Invaders got right here out, and bam! it exploded,” Mr. Kaplan acknowledged. Location Invaders used to be the most well-most well-liked sport within the arcades, and the VCS, with rows of six objects across the veil (two participant-objects, copied three cases every) might maybe well well recreate it within the dwelling.

One other hardware characteristic, one which undoubtedly cost an very excellent quantity of silicon, used to be vertical delay, or VDEL. The VCS writes two tv traces at a time, explained Mr. Miner, however involving objects by two traces between frames results in jerky lunge. A mode needed to be stumbled on to shift objects by easiest one line, and that means used to be VDEL. Two registers are used to bewitch care of the graphics info for every participant-object, and VDEL selects which register will be displayed on the veil.

The sequence of events is as follows: info sent to the tag registers for one participant object is loaded into its foremost register; when info is written to the rather a lot of participant object, the contents of the principle register for the principle object are robotically duplicated in its secondary register; if info for every participant object is written every rather a lot of scan line, the secondary register chosen by VDEL will tag the identical form as the principle register, however one line later. This system is now getting used to load rather a lot of information into the principle and secondary registers of every participant object, thus yielding single-line decision and rather a lot of unintended bonuses.

Early sport cartridges held easiest 2 kilobytes of ROM. “In 2K, you barely maintain room to brush your enamel.”

—Joe Decuir

Moreover being ready to resolve the form of an object, programmers can furthermore resolve its coloration and luminance. The decision to mosey with both coloration and luminance registers seemingly would now not had been made however for the simplicity of the coloration succor an eye on. Television coloration is definite by the variation in portion between the coloration signal and a reference signal, or coloration burst, that is transmitted within the starting assign of every line. The VCS’s portion shifter is nothing extra than a delay line tapped at appropriate intervals, and so it occupies somewhat exiguous chip assign.

An instance of intensive coloration manipulation is a subroutine developed by Mr. Decuir to succor away from burning sport patterns onto the TV veil if the VCS is left unattended. The routine, which cycled thru all seemingly coloration-luminance combos, used easiest a dozen bytes, a gargantuan advantage in early sport cartridges, which held easiest 2 kilobytes of ROM. “In 2K, you barely maintain room to brush your enamel,” Mr. Decuir acknowledged.

A the same form of results used to be produced and not using a much less than chip assign within the sound generator; it contains simply just a few dividers and polynomial counters that would be interconnected in a different of recommendations below program succor an eye on. A 5-bit polynomial counter, Mr. Decuir authorized, produces a low, grumbling sound (utilized in Tank), and a 9-bit counter produces a whooshing sound (utilized in Jet Fighter). The relaxation of the sounds that the programmers maintain made the VCS invent attain in point of fact free, and they also had been intensive—Mr. Mayer acknowledged he has even heard the VCS reproduce the phrases “E.T. phone home.”

Exploiting the Hardware

For the reason that VCS hardware does so exiguous on its have, a heavy burden is placed on the programmer. But though programming is exhausting, few partitions care for abet tool creativity.

“Writing the kernels that fabricate up the sport programs,” Mr. Mayer acknowledged, “is admire fixing acrostic puzzles with tons and tons of possibilities. There’s a obvious class of programmer that can maybe deal within the microcode admire that. If it had been easier to program, we would now not maintain these programmers, due to they’d be bored. The VCS is an absolute area.”

“One other skill of pronouncing it is a ways that to address a VCS you need to unlearn every loyal programming prepare you maintain realized,” acknowledged Mr. Mauer, who designed Location Invaders.

Bob Whitehead, senior vogue designer and cofounder of Activision Inc. in Mountain Learn about, Calif., could be the most revolutionary VCS vogue designer—he’s credited with the most firsts in using a original trick. But he’s philosophical about his improvements. “A laptop is a laptop,” he acknowledged, “and it easiest works in one skill. If one thing original comes up, it is adorable, however no extra than that, due to it is one thing the laptop has continually been ready to complete; you actual didn’t see it sooner than. It’s admire discovering a penny below the couch—it is continually been there, on the opposite hand it is adorable to see.”

“Writing the kernels that fabricate up the sport programs is admire fixing acrostic puzzles with tons and tons of possibilities.”

—Steve Mayer

Once a trick is stumbled on and is implemented in a sport, it turns into obvious to skilled VCS programmers, Mr. Whitehead authorized, and rapidly the trick is copied in rather a lot of games. Much less skilled programmers see at a program listing or bewitch up recommendations by observe of mouth.

This present day, on the opposite hand, designers estimate that the hardware has been 70 to 80 p.c exploited. “An increasing selection of the adorable things are now not showing up,” Mr. Whitehead acknowledged, “however then every time we see one thing original, we mediate that it is the closing thing.”

Altering Displays “On the Flit”

The foremost trick popped up when Mr. Whitehead designed Blackjack, and it is a ways now utilized in almost every VCS sport. It’s the functionality to rewrite participant objects “on the flit.” For the reason that microprocessor have to feed info every line to the “Stella” chip to fabricate a tag, it can swap the records even all the map thru a line to swap the looks of objects. The hardware can invent multiple copies of a participant object—a characteristic added so as that teams of biplanes might maybe well well fight every rather a lot of—and Mr. Whitehead stumbled on that he might maybe well well swap the displayed participant object between copies. In desire to placing up three copies of the identical object, the VCS then displays three rather a lot of objects: three rather a lot of cards within the case of Blackjack.

Objects can furthermore be rewritten as they are repositioned vertically, so the rather a lot of rows of aliens in Location Invaders see rather a lot of. This functionality used to be carried to an indecent in Activision’s Freeway, with 10 lanes of traffic and rather a lot of cars and autos in all places the veil. It used to be furthermore used very efficiently in Asteroids, in which the rocks that seem to be careening in all places the veil are in two rows, half of involving up and half of involving down.

A Few Tricks


“Venetian blinds” are utilized in Atari’s Chess sport to fabricate bigger the different of objects that would be displayed on one line.


The helicopter and laser that it fires in Activision’s Chopper Convey are created by writing playfield on the flit.


A swap in participant measurement on the flit extends the boxer’s arm into a punch in Activision’s Boxing.

But an preliminary limitation of rewriting participant objects on the flit used to be that the copied objects needed to circulate together, for the reason that VCS produces multiple photos easiest at assign spacings. A trick developed by Mr. Whitehead to allow many graphically rather a lot of objects to circulate independently is named flicker.

Flickering displays invent the semblance of extra self sustaining participant objects by showing the objects easiest every rather a lot of frame, or every third or fourth frame. The topic with this plan is that pronounced flicker can fabricate a sport refined or even inappropriate to play. Judiciously used, this tradeoff can fabricate games seemingly that the VCS otherwise might maybe well well now not address: Starship, in which the stars are made of participant objects that sparkle; Adventure, in which flicker occurs easiest when there are extra than two objects on the veil; baseball and football games; and Defender, to title just a few.

Satirically, flicker has on no narrative been used at Activision, the tool company that Mr. Whitehead helped open up when he left Atari in 1979. Mr. Whitehead did now not direct Activision will on no narrative utilize the technique in a sport, however he authorized that the corporate’s programmers will rethink the philosophy of a sport to succor away from it. “It’s miles a tradeoff that is now not acceptable,” he acknowledged.

Flicker would be performed with out if the lunge of objects is limited to succor them vertically separated, or by utilize of extra most up-to-date recommendations. Realistic the kind of recommendations is “venetian blinds,” and it used to be first utilized in Atari’s Chess sport.

Doing the “Impossible”: Chess

“When the VCS used to be first manufactured,” Mr. Kaplan recalled, “the sphere had a chess part on it. ‘Those marketing guys! Attain on,’ we acknowledged. ‘It’ll on no narrative cease chess.’ Well, some man in Florida sued due to there used to be a chess part on the quilt and we didn’t maintain a chess sport.”

A year later Atari’s designers began constructing Chess. “The guys had been taking part in around,” Allan Alcorn, then head of engineering at Atari, recalled, “and one man acknowledged, ‘I could maybe well well write an algorithm, however I could maybe well well now not salvage a playfield on the veil.’ One other man acknowledged, ‘That’s easy.’ ” Larry Wagner wrote the algorithm; it took him two years with the wait on of nationwide chess champion Julio Kaplan. Mr. Whitehead did the tag in two days, constructing the trick now identified as venetian blinds.

To tag eight chess pieces across the veil (as a change of the most six seemingly with triple copies), Mr. Whitehead displayed every object on every rather a lot of scan line. On the principle sweep across the veil, graphics for four objects had been displayed; on the next sweep, graphics for the rather a lot of four had been proven. The gaps had been obvious, however the chess pieces had been recognizable.

Whereas primitive in comparability with today’s chess machines, the Wagner-Whitehead chess sport, using 4 kilobytes of ROM and 138 bytes of random-salvage admission to memory, used to be as loyal as the chess machines then available on the market. There used to be easiest one area: the TV veil displayed random colors while the VCS calculated the next circulate; no processor time used to be left for the veil.

The venetian-blind technique has seemed in plenty of games since Chess. It used to be used for horses in Polo, a sport by Carol Shaw that used to be on no narrative launched, and in Frequent Programming to salvage 12 characters on a line. It used to be furthermore utilized in Stampede, by Mr. Whitehead , to animate the animals’ legs, and most fair recently, in Sky Jinks, furthermore by Mr. Whitehead, the assign parts of the balloon baskets are displayed on alternate traces. If used subtly, Mr. Whitehead authorized, the technique is now and again noticeable.

After that they had exploited adaptations on participant graphics, programmers grew to develop into to rather a lot of areas of the Stella chip to see for recommendations. One early discovery used to be that they would maybe maybe write the playfield—a low decision background 40 bits across—on the flit. Al Miller did this in Surround, the assign every block in a 40 by 24 grid would be grew to develop into on or off independently. The technique used to be utilized by Mr. Whitehead in Chopper Convey to invent an additional participant object—the chopper the participant commands.

Mr. Kaplan first rewrote coloration on the flit, altering coloration line by line to salvage a figure in his bowling sport that has a flesh-colored head, a blue shirt, gray trousers, and shaded sneakers. That technique used to be picked up in Superman to fabricate the frosty spirited film hero’s costume purple and blue, and it is a ways used broadly to tag brightly colored alien attackers, as effectively as scenery that appears to be to go as the colors deepen—including sunsets and oceans with rolling waves.

Mr. Whitehead indicated that after a sport is supplied any original recommendations used are apparent to skilled programmers. This thesis used to be confirmed by Spectrum‘s discovery that two tactics regarded as trade secrets and tactics by Activision at the time of writing had been broadly identified and, indeed, utilized by designers at rather a lot of video-sport companies.

Objects That Exchange Their Size

Realistic one of the most recommendations designers maintain pointed out exploits the functionality of the VCS to tag an object in well-liked, double, or quad width depending upon the rate at which the participant register is scanned. The trick comes in altering the size of the participant object on the flit. In Mr. Whitehead’s Boxing, the sport in which it is a ways believed this plan used to be first used, a swap in participant measurement extends the boxer’s arm into a punch. Mr. Whitehead furthermore used the technique in Skiing, and Brad Stewart at Imagic has integrated the trick in his most up-to-date sport, Sky Patrol.

One other trick first seemed within the sport Dragster. Designer David Crane, identified within the industry as “a coding machine,” wrote a complete kernel on the flit. The code, in spite of the entirety, does now not circulate physically, however somewhat moves in time, so as that the program is never any longer in synch with the tv assign, and what would otherwise be a static tag scrolls horizontally. When Dragster first seemed, the trick used to be regarded as now not doable to repeat, on the opposite hand it is a ways now understood all the map thru the industry. One vogue designer using it is a ways Imagic’s Bob Smith within the sport Dragonfire.

Possibly the final trick is being marketed by a company called Starpath, in Santa Clara, Calif.: a 6-kilobyte RAM module that suits into the VCS in assign of a cartridge and accepts tool from cassette tapes. (This possibility had been regarded as for the unique VCS however used to be discarded.) The prolonged RAM permits programmers to utilize graphics recommendations that can maybe well now not slot within the VCS’s 128 bytes—constantly finer decision and complex rewrite-on-the-flit tactics. Alongside with RAM to the VCS is anxious, n or is making cartridges with extra than 4 kilobytes of memory. In converse to place money, Atari restricted the cartridge connector to 24 pins, omitting read-write and clock traces for RAM, as effectively as traces for addresses better than 4096. Mr. Miner and Mr. Decuir agreed searching back that this decision used to be a mistake, since a 30-pin connector would maintain cost easiest 50 cents for every VCS and 10 cents a cartridge and would maintain allowed both RAM and a 64-kilobyte address assign.

Many companies now utilize 8-kilobyte cartridges by a skill called monetary institution switching, the assign a read from a obvious address triggers a flip-flop, directing all subsequent addresses to a obvious portion of memory. The foremost monetary institution-switched cartridge used to be a 6-kilobyte chess sport by Larry Wagner; the sport used to be “scrunched” to 4 kilobytes by Bob Whitehead, removing the need for monetary institution switching, sooner than it used to be marketed.

RAM in cartridges is made seemingly by resynthesizing clock signals for RAM from these timing traces that cease acquire their skill to the cartridge port. The elevated urge of instructions coping with the principle 256 bytes of memory by the 6502 is all that makes the VCS seemingly, and so the VCS makes utilize of the same tactics internally to preserve address assign. A read and a write name to the identical address might maybe well address two entirely separate registers, Mr. Miner authorized: the read-write line is in actuality getting used as one more address line, besides to its supposed cause.

Making the Hardware Work

The VCS fabricate, it now and again appears to be, affords almost limitless possibilities for programmers. However the basic fabricate of the machine did now not attain easy. The MOS structure used to be performed actual away on the veil of an computerized IC drafting machine, and circuit evaluation used to be performed with out refined instruments. Mr. Miner recalled simply counting the most different of gate delays in any line, adding the line delays, and multiplying by two for a security component. The foremost pass of silicon failed, he authorized, due to “there used to be one line that did now not mosey into the flip-flop I idea it did; it went around it thru 12 extra gates. That used to be twice as many gates as any rather a lot of line.”

The VCS used to be furthermore a near nightmare to invent, in step with the of us tantalizing. To illustrate, the mechanical fabricate specified two sizes of self-tapping screw, and few workers on the manufacturing line might maybe well well distinguish between the 2. If the nasty screw used to be used, it shaved out myriad steel filings that raised havoc with the inner circuitry. Additional, when unassembled cases had been kept for a time, the plastic would warp, and the 2 halves would now not longer fit together. Production workers realized the “VCS karate cut” to pop the cases together.

By constructing a machine with an neat structure that left all its inner workings accessible to the programmer, [the VCS creators] ended up—as did early producers of phonographs—constructing an industry.

Market Acceptance

Even supposing Atari used to be slack handing over the VCS to shops for the 1977 Christmas season, its sales quantity went from $60 million to $120 million that year. Mute, the corporate lost money. In 1978 Atari determined to fabricate 800,000 VCS machines, extra than twice as many as the year sooner than. A complete of 500,000 orders got right here in by slack summer, and after tumble shipments went out, they disappeared from shops’ shelves in just a few weeks. But few additional orders got right here, and Atari used to be left with 300,000 unsold machines; the corporate had doubled its sales quantity for the 2nd year in a row, Mr. Decuir remembers, and straightforward it lost money.

Warner Communications Inc., Contemporary York, had supplied Atari for $28 million in 1976, largely on the strength of expectations for the VCS. But “for two years,” Mr. Mayer recalled, “Atari managed to single-handedly crawl down the return on equity of Warner inventory by a vital quantity.” This present day, thanks largely to the success of the VCS, Atari is to blame for over half of of Warner’s complete profit.

Messrs. Mayer, Milner, Miner, and Decuir assign out to fabricate a easy consumer product that can maybe well promote for two or three years—somewhat longer than a dedicated sport. By constructing a machine with an neat structure that left all its inner workings accessible to the programmer, they ended up—as did early producers of phonographs—constructing an industry, one which today has over 70 companies competing for a part of the video-sport tool market, estimated this year at $2.4 billion.

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