Inventing the Atari 2600 – IEEE Spectrum
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Inventing the Atari 2600 – IEEE Spectrum


In late 1975, gross sales of gadgets that made it doable for shoppers to play Pong on house tv units had been booming. At Atari Inc., which had first launched Pong as an arcade recreation and had manufactured one of the vital fashionable house variations of Pong, engineers started searching for the subsequent arcade recreation to place in client arms, anticipating that folks would develop uninterested in two paddles and a ball.

They noticed Jet Fighter and Tank, however as a substitute of designing a customized chip for every recreation, as was accomplished for Pong, they deliberate a system that will play each video games, four-player Pong if anybody was , and probably a number of different, as but unknown video games. The system was to be primarily based on a microprocessor.

In a number of months, Atari’s designers in Grass Valley, Calif., had made a working prototype, and over the subsequent 12 months, designers from Grass Valley and from Sunnyvale, Calif., refined what was to be the Atari Video Laptop System (VCS). It was launched in 1977, and 6 years later ranks as one of the vital profitable microprocessor-based merchandise ever constructed, with over 12 million bought at about $140 apiece.

Success didn’t come with out issues. Manufacturing issues within the first two years triggered Atari losses estimated close to $25 million. However as soon as these issues had been solved and sufficient software program was developed, the VCS took off.


This text was first printed as “Design case historical past: the Atari Video Laptop System” within the March 1983 concern of IEEE Spectrum. A PDF model of the unique article together with images and technical diagrams is out there on IEEE Xplore.

It’s fashionable at present, not as a result of it does an admirable job of enjoying Jet Fighter and Tank, however as a result of its versatile design additionally permits it to play chess and baseball, in addition to Area Invaders, Pac-Man and most of the different arcade video games which were invented for the reason that VCS got here in the marketplace. Greater than 200 completely different recreation cartridges—the read-only recollections (ROMs) containing VCS software program—at the moment are in the marketplace, manufactured by about 40 firms, and new video games are continually being developed. An estimated 120 million cartridges have been bought at costs from $12 to $35, and the demand is such that, along with shopping for extra 6502 microcomputers than anybody else on this planet, Atari’s purchases of ROMs for its varied divisions is larger than that of all different firms on this planet mixed.

Atari and different video-game firms had been making microprocessor-based arcade video games for a while earlier than the VCS was developed, however the price of then-available processors—$100 or extra every—made the thought of a house client product primarily based on a microprocessor impractical. Then got here Chuck Peddle and the 6502.

Mr. Peddle, who had left Motorola for MOS Expertise after designing the MC6800 microprocessor, appeared at Wescon—the annual West Coast electronics present—in September 1975, providing to promote his new microprocessor by the barrel at $8 apiece. “In fact, nobody knew that he solely had one barrel to his identify,” recollects Steve Mayer, cofounder of Cyan Engineering, Atari’s personal consulting firm in Grass Valley, and now senior vp for R&D at Atari.

Mr. Mayer and Ron Milner, his colleague at Cyan, went to see Mr. Peddle at Wescon and located that the 6502 matched exactly the minimal specs that that they had laid out a while earlier than in a blue-sky design for a programmable online game. The three went into the again of the MOS Expertise suite, Mr. Mayer recollects, and in an hour the deal was struck. It began a revolution in house video video games.

Making an attempt to Survive

Nobody noticed it that method on the time. “We had been simply attempting to outlive,” Mr. Mayer informed Spectrum. Atari had entered the house video market with a one-chip model of its Pong arcade recreation, and it was growing different house video video games, however every was primarily based on a single customized chip that took a 12 months or extra and over $100,000 to develop—by the point an arcade recreation reached the house market, shoppers would have forgotten about it. A programmable house online game appeared a fascinating different.

The important thing to the design was simplicity: making the software program do as a lot of the work as doable, in order that the {hardware} may very well be cheaper—silicon was very costly in these days. The microprocessor was synchronized to the tv scan price and created the show one or two strains at a time. This synchronization reduces reminiscence necessities for the tv interface significantly, however the processor should regularly replace the registers within the interface to get any show in any respect. This system that feeds info to the video chip (known as Stella, after its designer’s bicycle) is named a kernel.

To additional scale back reminiscence necessities, Mr. Mayer and Mr. Milner determined to show the background of the display at comparatively low decision, whereas displaying shifting objects with increased decision—low-resolution playfield, high-resolution gamers. In addition they eradicated any provision for vertical synchronization and gave that job to the programmer. A VCS kernel should rely the variety of strains displayed on the tv display and should end displaying a single body in precisely the identical time—15.24 milliseconds—that it takes the TV set’s electron gun to make a single top-to-bottom sweep.

The important thing to the design was simplicity: making the software program do as a lot of the work as doable, in order that the {hardware} may very well be cheaper.

Two prototypes of the Stella had been constructed: a purposeful prototype constructed by Mr. Milner to check the idea, and a gate-level prototype constructed by Joe Decuir, who was employed by Cyan in late 1975. The gate-level prototype was designed to imitate as intently as doable the meant ultimate chip, utilizing circuit-design strategies particular to MOS built-in circuits.

One crucial MOS-dependent characteristic was using a particular counter—known as a polynomial counter, or pseudorandom shift register—as a substitute of a real binary counter to find out object positions on the display. A polynomial counter occupies one-fourth the silicon space of an equal binary counter, however, not like a binary counter, it doesn’t rely in any easy order. Thus, a programmer can’t calculate a display place for an object and cargo it into the place counter.

The unique Stella prototype had just one sign to the place counter: a reset that will set off the speedy show of an object. Mr. Decuir and Jay Miner, who designed the manufacturing model of the Stella chip, used this identical idea of their design. Because of this, displaying an object in a given place on the display requires that the programmer rely the variety of clock cycles taken by a given set of directions, determine how far throughout the display the electron beam could be after the directions had been executed, and act accordingly. As soon as the place counter for an object is reset on the correct level, it continues to show the item at that spot on succeeding strains.

To maneuver objects, the prototype blocked out 4 clock pulses from the place counters in the course of the vertical blanking interval; a programmer may then add pulses to maneuver an object left or proper—4 pulses needed to be added to maintain the item in the identical place. Mr. Miner added a set of movement registers, which add or subtract pulses robotically when a sign—known as H-move—is distributed by the microprocessor. The H-move might be despatched in the course of the vertical blanking interval, or in the course of the horizontal blanking interval initially of every line.

“This appeared innocuous sufficient,” stated Larry Kaplan, the primary software program designer employed to develop video games for the Stella challenge. “However I found early that it was doable to reposition participant objects throughout a display [a frame of the TV picture], although that was not a consideration of the design.”

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

Joe Decuir drew this circuit diagram of what was to grow to be the Atari Video Laptop System on 8 November 1976.

Joe Decuir

So Mr. Kaplan designed Air-Sea Battle, which has horizontal bands of participant objects, a way utilized in numerous VCS video games, together with Area Invaders, Freeway, Asteroids, and Soccer. “With out that single strobe, H-move, the VCS would have died a fast loss of life 5 years in the past,” stated Mr. Kaplan, now vp of product growth at Atari.

H-move and a characteristic that allowed two or three copies of an object to be positioned on the display let one other VCS programmer, Rick Mauer, design a house model of the arcade hit, Area Invaders. That recreation hit the arcades in 1979, when the VCS was going downhill after dropping cash in 1977 and 1978.

“The VCS was not doing that effectively—there have been just a few million within the subject, and it regarded prefer it was dying—then Area Invaders got here out, and bam! it exploded,” Mr. Kaplan stated. Area Invaders was the most well-liked recreation within the arcades, and the VCS, with rows of six objects throughout the display (two player-objects, copied 3 times every) may recreate it within the house.

One other {hardware} characteristic, one that truly price a good quantity of silicon, was vertical delay, or VDEL. The VCS writes two tv strains at a time, defined Mr. Miner, however shifting objects by two strains between frames results in jerky movement. A method needed to be discovered to shift objects by just one line, and that method was VDEL. Two registers are used to carry the graphics info for every player-object, and VDEL selects which register will likely be displayed on the display.

The sequence of occasions is as follows: info despatched to the show registers for one participant object is loaded into its major register; when info is written to the opposite participant object, the contents of the first register for the primary object are robotically duplicated in its secondary register; if info for every participant object is written each different scan line, the secondary register chosen by VDEL will show the identical form as the first register, however one line later. This method is now getting used to load completely different info into the first and secondary registers of every participant object, thus yielding single-line decision and different unintended bonuses.

Early recreation cartridges held solely 2 kilobytes of ROM. “In 2K, you barely have room to brush your tooth.”

—Joe Decuir

Along with having the ability to decide the form of an object, programmers may decide its coloration and luminance. The choice to go along with each coloration and luminance registers in all probability wouldn’t have been made however for the simplicity of the colour management. Tv coloration is decided by the distinction in part between the colour sign and a reference sign, or coloration burst, that’s transmitted initially of every line. The VCS’s part shifter is nothing greater than a delay line tapped at applicable intervals, and so it occupies pretty little chip area.

An instance of intensive coloration manipulation is a subroutine developed by Mr. Decuir to keep away from burning recreation patterns onto the TV display if the VCS is left unattended. The routine, which cycled by all doable color-luminance combos, used solely a dozen bytes, an important benefit in early recreation cartridges, which held solely 2 kilobytes of ROM. “In 2K, you barely have room to brush your tooth,” Mr. Decuir stated.

The same number of results was produced with a minimal of chip area within the sound generator; it comprises merely a number of dividers and polynomial counters that may be interconnected in a variety of methods beneath program management. A 5-bit polynomial counter, Mr. Decuir famous, produces a low, grumbling sound (utilized in Tank), and a 9-bit counter produces a whooshing sound (utilized in Jet Fighter). The remainder of the sounds that the programmers have made the VCS produce come primarily free, they usually have been in depth—Mr. Mayer stated he has even heard the VCS reproduce the phrases “E.T. telephone house.”

Exploiting the {Hardware}

As a result of the VCS {hardware} does so little by itself, a heavy burden is positioned on the programmer. However although programming is arduous, few partitions maintain again software program creativity.

“Writing the kernels that make up the sport packages,” Mr. Mayer stated, “is like fixing acrostic puzzles with heaps and many potentialities. There is a sure class of programmer that may deal within the microcode like that. If it had been simpler to program, we would not have these programmers, as a result of they’d be bored. The VCS is an absolute problem.”

“One other method of claiming it’s that to take care of a VCS you need to unlearn each good programming observe you have realized,” stated Mr. Mauer, who designed Area Invaders.

Bob Whitehead, senior designer and cofounder of Activision Inc. in Mountain View, Calif., often is the most progressive VCS designer—he’s credited with essentially the most firsts in utilizing a brand new trick. However he’s philosophical about his improvements. “A pc is a pc,” he stated, “and it solely works in a technique. If one thing new comes up, it is cute, however not more than that, as a result of it is one thing the pc has all the time been capable of do; you simply did not uncover it earlier than. It is like discovering a penny beneath the sofa—it is all the time been there, nevertheless it’s cute to find.”

“Writing the kernels that make up the sport packages is like fixing acrostic puzzles with heaps and many potentialities.”

—Steve Mayer

As soon as a trick is found and is applied in a recreation, it turns into apparent to skilled VCS programmers, Mr. Whitehead famous, and shortly the trick is copied in different video games. Much less skilled programmers take a look at a program itemizing or decide up methods by phrase of mouth.

At the moment, nonetheless, designers estimate that the {hardware} has been 70 to 80 % exploited. “Increasingly the lovable issues aren’t displaying up,” Mr. Whitehead stated, “however then each time we uncover one thing new, we predict that it’s the final thing.”

Altering Shows “On the Fly”

The primary trick popped up when Mr. Whitehead designed Blackjack, and it’s now utilized in almost each VCS recreation. It’s the functionality to rewrite participant objects “on the fly.” As a result of the microprocessor should feed info each line to the “Stella” chip to make a show, it will probably change the knowledge even throughout a line to vary the looks of objects. The {hardware} can produce a number of copies of a participant object—a characteristic added in order that teams of biplanes may combat one another—and Mr. Whitehead found that he may change the displayed participant object between copies. As an alternative of placing up three copies of the identical object, the VCS then shows three completely different objects: three completely different playing cards within the case of Blackjack.

Objects can be rewritten as they’re repositioned vertically, so the completely different rows of aliens in Area Invaders look completely different. This functionality was carried to an excessive in Activision’s Freeway, with 10 lanes of site visitors and completely different vehicles and vans all around the display. It was additionally used very efficiently in Asteroids, by which the rocks that look like careening all around the display are in two rows, half shifting up and half shifting down.

A Few Methods

01

“Venetian blinds” are utilized in Atari’s Chess recreation to extend the variety of objects that may be displayed on one line.

02

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

03

A change in participant dimension on the fly extends the boxer’s arm right into a punch in Activision’s Boxing.

However an preliminary limitation of rewriting participant objects on the fly was that the copied objects needed to transfer collectively, as a result of the VCS produces a number of photographs solely at set spacings. A trick developed by Mr. Whitehead to permit many graphically completely different objects to maneuver independently is named flicker.

Flickering shows create the phantasm of additional unbiased participant objects by displaying the objects solely each different body, or each third or fourth body. The issue with this system is that pronounced flicker could make a recreation troublesome and even disagreeable to play. Judiciously used, this tradeoff could make video games doable that the VCS in any other case couldn’t deal with: Starship, by which the celebrities are manufactured from participant objects that sparkle; Journey, by which flicker happens solely when there are greater than two objects on the display; baseball and soccer video games; and Defender, to call a number of.

Sarcastically, flicker has by no means been used at Activision, the software program firm that Mr. Whitehead helped begin when he left Atari in 1979. Mr. Whitehead didn’t say Activision won’t ever use the approach in a recreation, however he famous that the corporate’s programmers will rethink the philosophy of a recreation to keep away from it. “It’s a tradeoff that isn’t acceptable,” he stated.

Flicker might be averted if the movement of objects is restricted to maintain them vertically separated, or by use of newer methods. A type of methods is “venetian blinds,” and it was first utilized in Atari’s Chess recreation.

Doing the “Inconceivable”: Chess

“When the VCS was first manufactured,” Mr. Kaplan recalled, “the field had a chess piece on it. ‘These advertising and marketing guys! Come on,’ we stated. ‘It will by no means do chess.’ Properly, some man in Florida sued as a result of there was a chess piece on the quilt and we did not have a chess recreation.”

A 12 months later Atari’s designers started growing Chess. “The blokes had been enjoying round,” Allan Alcorn, then head of engineering at Atari, recalled, “and one man stated, ‘I may write an algorithm, however I could not get a playfield on the display.’ One other man stated, ‘That is straightforward.’ ” Larry Wagner wrote the algorithm; it took him two years with the assistance of nationwide chess champion Julio Kaplan. Mr. Whitehead did the show in two days, growing the trick now generally known as venetian blinds.

To show eight chess items throughout the display (as a substitute of the utmost six doable with triple copies), Mr. Whitehead displayed every object on each different scan line. On the primary sweep throughout the display, graphics for 4 objects had been displayed; on the subsequent sweep, graphics for the opposite 4 had been proven. The gaps had been apparent, however the chess items had been recognizable.

Whereas primitive as compared with at present’s chess machines, the Wagner-Whitehead chess recreation, utilizing 4 kilobytes of ROM and 138 bytes of random-access reminiscence, was nearly as good because the chess machines then in the marketplace. There was just one downside: the TV display displayed random colours whereas the VCS calculated the subsequent transfer; no processor time was left for the display.

The venetian-blind approach has appeared in lots of video games since Chess. It was used for horses in Polo, a recreation by Carol Shaw that was by no means launched, and in Fundamental Programming to get 12 characters on a line. It was additionally utilized in Stampede, by Mr. Whitehead , to animate the animals’ legs, and most not too long ago, in Sky Jinks, additionally by Mr. Whitehead, the place components of the balloon baskets are displayed on alternate strains. If used subtly, Mr. Whitehead famous, the approach is hardly noticeable.

After that they had exploited variations on participant graphics, programmers turned to different areas of the Stella chip to search for methods. One early discovery was that they might write the playfield—a low decision background 40 bits throughout—on the fly. Al Miller did this in Encompass, the place every block in a 40 by 24 grid might be turned on or off independently. The approach was utilized by Mr. Whitehead in Chopper Command to create an additional participant object—the chopper the participant instructions.

Mr. Kaplan first rewrote coloration on the fly, altering coloration line by line to get a determine in his bowling recreation that has a flesh-colored head, a blue shirt, grey trousers, and black sneakers. That approach was picked up in Superman to make the cartoon hero’s costume crimson and blue, and it’s used extensively to show brightly coloured alien attackers, in addition to surroundings that seems to recede as the colours deepen—together with sunsets and oceans with rolling waves.

Mr. Whitehead indicated that when a recreation is in the marketplace any new methods used are obvious to skilled programmers. This thesis was confirmed by Spectrum‘s discovery that two strategies thought-about commerce secrets and techniques by Activision on the time of writing had been extensively identified and, certainly, utilized by designers at different video-game firms.

Objects That Change Their Dimension

One of many methods designers have identified exploits the potential of the VCS to show an object in regular, double, or quad width relying upon the speed at which the participant register is scanned. The trick is available in altering the dimensions of the participant object on the fly. In Mr. Whitehead’s Boxing, the sport by which it’s believed this system was first used, a change in participant dimension extends the boxer’s arm right into a punch. Mr. Whitehead additionally used the approach in Snowboarding, and Brad Stewart at Imagic has included the trick in his latest recreation, Sky Patrol.

One other trick first appeared within the recreation Dragster. Designer David Crane, identified within the business as “a coding machine,” wrote a whole kernel on the fly. The code, in fact, doesn’t transfer bodily, however somewhat strikes in time, in order that this system is now not in synch with the tv set, and what would in any other case be a static show scrolls horizontally. When Dragster first appeared, the trick was thought-about unimaginable to repeat, however it’s now understood all through the business. One designer utilizing it’s Imagic’s Bob Smith within the recreation Dragonfire.

Maybe the last word trick is being marketed by an organization known as Starpath, in Santa Clara, Calif.: a 6-kilobyte RAM module that matches into the VCS rather than a cartridge and accepts software program from cassette tapes. (This feature had been thought-about for the unique VCS however was discarded.) The prolonged RAM permits programmers to make use of graphics methods that will not match within the VCS’s 128 bytes—persistently finer decision and complicated rewrite-on-the-fly strategies. Including RAM to the VCS is just not straightforward, n or is making cartridges with greater than 4 kilobytes of reminiscence. With a view to get monetary savings, Atari restricted the cartridge connector to 24 pins, omitting read-write and clock strains for RAM, in addition to strains for addresses larger than 4096. Mr. Miner and Mr. Decuir agreed looking back that this resolution was a mistake, since a 30-pin connector would have price solely 50 cents for every VCS and 10 cents a cartridge and would have allowed each RAM and a 64-kilobyte deal with area.

Many firms now use 8-kilobyte cartridges via a way known as financial institution switching, the place a learn from a sure deal with triggers a flip-flop, directing all subsequent addresses to a special part of reminiscence. The primary bank-switched cartridge was a 6-kilobyte chess recreation by Larry Wagner; the sport was “scrunched” to 4 kilobytes by Bob Whitehead, eliminating the necessity for financial institution switching, earlier than it was marketed.

RAM in cartridges is made doable by resynthesizing clock indicators for RAM from these timing strains that do discover their option to the cartridge port. The elevated velocity of directions coping with the primary 256 bytes of reminiscence by the 6502 is all that makes the VCS doable, and so the VCS makes use of comparable strategies internally to preserve deal with area. A learn and a write name to the identical deal with could take care of two utterly separate registers, Mr. Miner famous: the read-write line is definitely getting used as one other deal with line, along with its meant objective.

Making the {Hardware} Work

The VCS design, it typically appears, affords almost limitless potentialities for programmers. However the fundamental design of the machine didn’t come straightforward. The MOS format was accomplished straight on the display of an automatic IC drafting system, and circuit evaluation was carried out with out subtle instruments. Mr. Miner recalled merely counting the utmost variety of gate delays in any line, including the road delays, and multiplying by two for a security issue. The primary go of silicon failed, he famous, as a result of “there was one line that did not go into the flip-flop I assumed it did; it went round it by 12 extra gates. That was twice as many gates as every other line.”

The VCS was additionally a close to nightmare to supply, in keeping with the folks concerned. For instance, the mechanical design specified two sizes of self-tapping screw, and few employees on the manufacturing line may distinguish between the 2. If the incorrect screw was used, it shaved out myriad metallic filings that raised havoc with the inside circuitry. Additional, when unassembled circumstances had been saved for a time, the plastic would warp, and the 2 halves wouldn’t longer match collectively. Manufacturing employees realized the “VCS karate chop” to pop the circumstances collectively.

By making a machine with a chic structure that left all its internal workings accessible to the programmer, [the VCS creators] ended up—as did early producers of phonographs—creating an business.

Market Acceptance

Regardless that Atari was late delivering the VCS to retailers for the 1977 Christmas season, its gross sales quantity went from $60 million to $120 million that 12 months. Nonetheless, the corporate misplaced cash. In 1978 Atari determined to construct 800,000 VCS machines, greater than twice as many because the 12 months earlier than. A complete of 500,000 orders got here in by late summer time, and after fall shipments went out, they disappeared from retailers’ cabinets in a number of weeks. However few extra orders got here, and Atari was left with 300,000 unsold machines; the corporate had doubled its gross sales quantity for the second 12 months in a row, Mr. Decuir recollects, and nonetheless it misplaced cash.

Warner Communications Inc., New York, had purchased Atari for $28 million in 1976, largely on the energy of expectations for the VCS. However “for 2 years,” Mr. Mayer recalled, “Atari managed to single-handedly drag down the return on fairness of Warner inventory by a big quantity.” At the moment, thanks largely to the success of the VCS, Atari is answerable for over half of Warner’s complete revenue.

Messrs. Mayer, Milner, Miner, and Decuir got down to make a easy client product that will promote for 2 or three years—barely longer than a devoted recreation. By making a machine with a chic structure that left all its internal workings accessible to the programmer, they ended up—as did early producers of phonographs—creating an business, one which at present has over 70 firms competing for a share of the video-game software program market, estimated this 12 months at $2.4 billion.

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