Toru Iwatani and Pac-Man

A Pinball Designer Without Pinball

Toru Iwatani was born on January 25, 1955, in Meguro, Tokyo. He had no formal training in programming or design; he taught himself, and joined Namco in 1977 at age 22 hoping to make pinball machines. Namco did not make pinball machines. Iwatani’s compromise was Gee Bee (1978), a video game with pinball physics, followed by the sequels Bomb Bee and Cutie Q (1979). None of them made him a name.

Designing for Dates

By late 1979, Iwatani had a diagnosis for the arcade business: everything was violent, and everything was aimed at men. His stated goal for the next project was a game that women and couples would play. His reasoning ran through food (“women like to eat sweets”), so the design became eating: a maze, dots, a mouth. The name came from the Japanese onomatopoeia paku paku, the sound of munching.

A team of nine, including programmers Shigeo Funaki and Shigeichi Ishimura and composer Toshio Kai, spent one year and five months on the game, reportedly the longest development of any video game to that date. It was test-marketed in Japan on May 22, 1980, as Puck Man. For the October 1980 North American release through Midway, the name became Pac-Man, because a cabinet that says PUCK is one scratched letter away from a word arcade operators did not want on their floor.

Four Ghosts, Four Personalities

Iwatani’s design problem was making four enemies feel dangerous but fair. If all ghosts used the same logic, they would form a single-file conga line behind the player. His solution became a founding example of video game AI: each ghost got its own targeting rule.

• Blinky (red, “chaser”) targets Pac-Man’s tile directly.
• Pinky (pink, “ambusher”) targets the tile four steps ahead of Pac-Man, cutting off escape routes.
• Inky (cyan, “fickle”) draws a vector from Blinky through the tile ahead of Pac-Man and doubles it, so his behavior depends on where Blinky is.
• Clyde (orange) chases like Blinky until he gets close, then retreats to his corner.

The ghosts also periodically switch from chase mode to a “scatter” mode, each heading for its home corner, giving the player breathing room on a schedule. The combination produces pursuit that feels coordinated without any coordination in the code.

The Bug: Ghosts Cannot Look Up

In 2008, the programmer Don Hodges disassembled the original Z80 code and documented a flaw players had half-noticed for decades. Direction vectors are stored as two signed bytes packed into one 16-bit register pair; “up” is (−1, 0). To find the tile four steps ahead, the code doubles the vector twice with 16-bit ADD HL,HL instructions. For up, the low byte’s arithmetic carries into the high byte, corrupting it: instead of “four tiles up,” the result is “four tiles up and four tiles left.” Pinky therefore ambushes a phantom position whenever Pac-Man faces up, and Inky, whose calculation reuses the same routine, inherits the same error. The bug shipped in every cabinet and was faithfully reproduced in ports for decades; players exploited it without knowing why facing upward made ambushes miss. It sits in the same family as every other packed-integer accident in this encyclopedia: a representation chosen for efficiency, betrayed by a carry bit.

Level 256

The level counter is a single byte. On the 256th board, it wraps to zero, and the routine that draws the fruit icons at the bottom of the screen, which expects a small number, instead tries to draw 256 of them, scribbling symbols across the right half of the maze. Half the dots become unreachable, the board cannot be cleared, and the game ends there for everyone, always. The kill screen made Pac-Man finite, which made it perfectable: eat every dot, energizer, fruit, and all four ghosts on every energizer for 255 boards, then squeeze the maximum from the broken board, and the score is exactly 3,333,360. Billy Mitchell recorded the first publicly verified perfect game on July 3, 1999. (Mitchell later became the center of the score-verification scandals around Donkey Kong; Twin Galaxies stripped all his records, including this Pac-Man score, in 2018. The perfect game itself is a real, well-defined feat, independently achieved and speedrun by others since.)

Success Without a Bonus

Pac-Man sold over 100,000 cabinets in its first year and about 400,000 by 1982, passing $1 billion in quarters within a year of launch; Guinness certified 293,822 installed machines as a world record in 2010, and total revenue across all versions passed $12 billion by 2016. It was the first video game character to break into merchandising at scale, the subject of a hit novelty song, and the game that put women in arcades. Iwatani, a salaried employee, received no bonus and no raise. Ms. Pac-Man (1982), the even-better-regarded sequel, was not his or Namco’s design at all: it began as an enhancement kit by General Computer Corporation, a Massachusetts startup, which Midway turned into an official product. The one famous Pac-Man disaster, the degraded Atari 2600 port that helped trigger the 1983 crash, is told in The Video Game Industry.

Iwatani stayed at Namco for thirty years, producing titles including Ridge Racer and Time Crisis, and left in March 2007 to become a professor at Tokyo Polytechnic University, teaching game design. At the 2011 Game Developers Conference he finally gave a postmortem of Pac-Man, thirty-one years late, to a packed room.

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📚 Sources

• Pac-Man — Wikipedia
• Tōru Iwatani — Wikipedia
• Hodges, Don: “Why do Pinky and Inky have different behaviors when Pac-Man is facing up?” — donhodges.com (2008), Z80 disassembly of the targeting bug
• Hodges, Don: “How High Can You Get?” — donhodges.com, disassembly of the level 256 kill screen