Atari’s own programming guide for its console admits that the machine’s memory works on hope. The Video Computer System has 128 bytes of RAM, and the guide tells programmers to put their variables at the bottom and the processor’s stack at the top, “hoping the two never meet”. There is no screen memory at all. A 2600 game draws its picture by feeding the graphics chip one line at a time, in step with the television’s electron beam.
That machine sold in the millions and became what “Atari” meant to a generation of North American players. It went on sale in 1977, sold slowly at first, took off after Atari licensed Space Invaders, and was still in production when Atari finally dropped it at the end of 1991.
Fast facts
- Launch: shown at the summer Consumer Electronics Show in 1977 and shipped for that Christmas.
- Price: $180 in period accounts. Later histories often give $199.
- CPU: MOS 6507, a 6502 in a 28-pin package with 13 address lines, at about 1.19 MHz (the 3.58 MHz colour clock divided by three).
- Graphics and sound: the TIA (Television Interface Adaptor).
- RAM: 128 bytes, inside the 6532 RIOT chip that also handles the controllers, console switches and a timer.
- Cartridges: 2K and 4K at first; 8K from Asteroids on, using bank switching.
- Model number: CX2600, the name it was later known by.
Who built it
“Credit for the VCS usually goes to Nolan Bushnell,” Antic told its readers in 1983. “Actually, it was principally invented by Atari’s Steven T. Mayer.” Video Games had reported in 1982 that the VCS, code-named Stella, was “conceptualized at Atari’s Grass Valley think tank, primarily by Steve Meyer” [Mayer], and developed at Los Gatos “by a group of engineers led by Jay Minor” [Miner]. Doug Neubauer, who designed the Atari 800’s sound chip, said the 800 grew out of the 2600 and was “conceived primarily by Steve Mayer, Joe Decuir and Jay Miner”. Miner designed the VCS’s custom chip, the TIA.
Warner Communications had bought Atari in October 1976, and the first two years of the VCS were hard. After the 1977 debut, Video Games wrote, “sales were soft and stayed that way throughout the following year”. With Warner’s money, Atari built 800,000 consoles in 1978 and was left with about 400,000 in the warehouse. “Clearly we built too many units,” said Joe Keenan, Atari’s president at the time, “$40 million worth of inventory that the company was stuck with.” Alan Miller, who wrote some of the first cartridges, blamed the price: shoppers could buy a dedicated game for $30 to $50 or “slap down $180 for the VCS”.
Racing the beam
The TIA does not hold a picture. It holds one line. Atari’s Stella Programmer’s Guide puts it plainly: “the actual TV picture is drawn one line at time by having the microprocessor enter the data for that line into the Television Interface Adapter”. Because the chip only knows about the line being drawn, the processor “must be ‘one step ahead’ of the electron beam on each line”.
Each line lasts 228 colour clocks: 68 of horizontal blanking and 160 of picture. The processor runs at a third of that rate, so a program gets 76 machine cycles per line to set up the next one. An NTSC frame has 262 lines. The guide gives 192 of them to the picture and leaves 70 for vertical sync, blanking and overscan, which is where a game does its thinking: about 5,320 cycles for movement, scoring and reading the controls.
Programmers could not count every branch exactly, so the TIA offers a way to catch up. A write to its WSYNC register halts the processor until the beam reaches the right edge of the screen. The processor then starts again at the beginning of the next line’s blanking period. The guide notes it was “customary (but not required)” to update the TIA only every two lines, trading vertical detail for time.
Carol Shaw, who wrote River Raid for Activision, compared it with Mattel’s Intellivision in 1983: “On the 2600, every line in your program is deciding what to display.” On the Intellivision you describe the screen and the hardware draws it, she said, “and you can’t go in and change something in the middle of the screen as easily.” Miller told Computer Gaming World in 1986 that because “all the parameters pertaining to display output were specifically under software control”, it was “a vastly more configurable machine than anyone thought it would be”.
What the TIA draws
The guide lists what a programmer has to work with:
- Playfield: a 20-bit pattern covering the left half of the screen. The right half repeats it, either copied or mirrored. It is meant for walls, clouds and barriers, and it “must be completely re-drawn in order to make it ‘move’”.
- Two players: 8-bit-wide graphics, drawn a line at a time. To place one vertically, you leave its register empty until the beam reaches the right line, then write the shape line by line. Each player can be mirrored, stretched to double or quadruple width, or copied up to three times across the line.
- Two missiles and a ball: one bit wide, for bullets and similar small objects.
- Colour: 16 colours at 8 brightness levels, but only four colour registers, shared in pairs, so a line has at most four colours unless the program changes a register while the line is drawn.
- Sound: two channels. Each has a 4-bit control for the type of sound, from pure tones “like a flute” to noise “like a rocket motor or explosion”, a 4-bit volume, and a 5-bit value that divides a 30 kHz reference. Dividing a fixed frequency by a 5-bit number gives each type of sound only 32 pitches, unevenly spaced, so many musical notes are simply not available.
- Collisions: the TIA latches every overlap between objects, and the program reads them afterwards.
128 bytes, and a hope
The machine’s RAM sits inside the 6532 chip. The guide’s full description: “The PIA has 128 bytes of RAM located in the STELLA map from HEX address $80 to $FF. The microprocessor stack is normally located from $FF downward, and variables are normally located from $80 upward (hoping the two never meet).”
Every score, position, timer and return address in a 2600 game fits in that space. There is no memory protection and nothing to warn a program when the stack runs into its variables.
Cartridges and bank switching
The 6507 has 13 address lines, so it can see only 8K of address space, and the cartridge gets 4K of it. Early games were smaller still. Shaw recalled that Activision “started out with 2K carts, then doubled the size to 4K and now we’re at 8K.”
Bigger games needed a trick. Electronic Games explained it to a reader in November 1982: as of Asteroids and Missile Command, the VCS “is capable of up to 8K, using a special bank switch that flip-flops two 4K programs”. The cartridge contains more ROM than the processor can see, and reading or writing particular addresses tells the cartridge’s own logic which 4K bank to show. See bank switching.
Space Invaders and the boom
Atari acquired the home rights to Taito’s Space Invaders in 1980 and showed the VCS cartridge at the New York Toy Fair on 10 February. Electronic Games judged in 1981 that “this one overwhelmingly desirable title sold the entire VCS system in many cases”, and Antic dated the machine’s success from its arrival: “It wasn’t until Bushnell left Atari in January of 1979 that Space Invaders arrived and the VCS took off.”
Some of Atari’s programmers left to sell games of their own. Alan Miller left at the end of 1979 “with a couple of other game designers” to form Activision, because, he said later, Atari “had lost their striving for technical excellence”. Others followed, and by 1982 more than a dozen outside companies were making 2600 cartridges, with no say from Atari over what they released. See Atari vs Activision.
How many consoles Atari sold depends on who was counting. Video Games put the number of owners in the US at “nearly 12 million” in June 1983. ANALOG Computing wrote of “almost 15 million 2600 game machines” in 1984, and by March 1986 it reported “more than 25 million 2600s” sold worldwide. Later figures are higher still, and none of them rests on a published Atari total.
The crash
The boom ended in the 1983 video game crash. Too many consoles and too many cartridges met falling demand. Atari’s rushed 2600 Pac-Man disappointed players who knew the arcade game, and E.T. the Extra-Terrestrial was made in five weeks for Christmas 1982. Atari lost $539 million in 1983, and in July 1984 Warner sold the consumer business to Jack Tramiel.
The 2600 survived the sale. In Britain, where it had been sold since 1978, TV Gamer listed it at £69.95 with two joysticks, two paddles and two cartridges at the end of 1983, “the most widely sold system in the world”. ST Action recalled in 1988 that Tramiel’s first move was “to lower the price of the VCS, improve the product and continue with the business”. According to AtariUser, Atari decided to discontinue it, with the 7800 and the XE Game System, as of Christmas 1991.
From the TIA to the Amiga
The TIA was the first of three display designs by Jay Miner, and each moved more of the work away from the processor. On the 2600 the 6507 builds every line itself. On the Atari 400 and 800, Miner’s team designed ANTIC, a display processor that runs its own program, the display list, every frame. On the Amiga, the copper runs a list of instructions timed to the beam and the blitter moves graphics without the CPU.
Sources
- Steve Wright, Stella Programmer’s Guide (Atari, 1979; updated by Darryl May, 1988): the TV picture and the kernel; TIA sections 3.1–3.3 (timing and WSYNC), 4.0 (colour and luminosity), 5.0 (playfield), 6.0–6.3 (players, missiles and ball), 10.0 (collisions), 11.0–11.3 (sound); PIA section 3.0 (RAM).
- Atari, 2600/2600A VCS Domestic Field Service Manual (1983): theory of operation (6507, TIA and 6532) and address lines AB0–AB12.
- Atari, Video Computer System Owner’s Manual (1980): model CX2600.
- Steve Bloom, “The incredible, incredible story of Atari”, Video Games, vol. 1 no. 3, December 1982, pp. 36–47: Warner’s purchase in October 1976; Stella, Steve Mayer and Jay Miner (pp. 44–45); the summer CES debut, soft sales, the $180 price, 800,000 consoles built in 1978 and 400,000 unsold, Joe Keenan’s “$40 million”.
- Dan Gutman, Antic, vol. 2 no. 2, May 1983, p. 61: 1977 launch, $180 price, Steve Mayer, Space Invaders, the 6507.
- Lee H. Pappas, “An interview with Doug Neubauer”, ANALOG Computing issue 47, October 1986, p. 89: the 800 “conceived primarily by Steve Mayer, Joe Decuir and Jay Miner” as an upgrade of the 2600.
- Amiga Computing, December 1988: Jay Miner “had designed the chips in the Atari 800 and the VCS”.
- Randi Hacker, “Gamemakers: Designing Woman”, Electronic Fun with Computers & Games, September 1983, p. 61: interview with Carol Shaw.
- Computer Gaming World issue 32, November 1986: interview with Alan Miller (programming the 2600, leaving Atari, founding Activision).
- Electronic Games, November 1982, p. 102: Q&A on 8K bank-switched cartridges.
- Compute! issue 3, April 1980: Atari news release on the Space Invaders licence and the Toy Fair of 10 February 1980.
- Electronic Games, vol. 1 no. 1, Winter 1981, pp. 31–32: Atari’s purchase of the home rights to Space Invaders in 1980.
- Video Games, June 1983: “nearly 12 million Atari VCS owners in the U.S.”
- ANALOG Computing issue 21, August 1984: “almost 15 million 2600 game machines”; Arthur Leyenberger, “Winter CES”, ANALOG Computing issue 40, March 1986, p. 24: “more than 25 million 2600s”.
- TV Gamer, December 1983: launched “USA 1977, UK 1978”, price £69.95.
- Retro Gamer issue 100, March 2012, pp. 90–95: outside publishers; Atari’s 1983 loss and the sale to Tramiel.
- ST Action, vol. 1 no. 4, August 1988: Tramiel’s Atari and the VCS.
- AtariUser issue 15, July 1992, “The Game’s the Thing”: the 2600 discontinued as of Christmas 1991.
- The Atari Book (Retro Gamer, 2012): the $199 launch price given by later histories.