Racing the Beam : the Atari Video Computer System - Index of

A year later, Atari released an adaptation of Ms. Pac-Man that
responded to most of the gripes that players had about VCS Pac-Man. Part
of this work was derivative of Frye’s. Part of it benefi ted from the perfect
hindsight of the original VCS Pac-Man debacle.
For one thing, the game used an 8K ROM instead of the 4K ROM that
Frye was allotted for his project thanks to a technique called bankswitching.
The 6507 microprocessor used in the Atari VCS featured only
thirteen of the sixteen pins available in the 6502. This limitation reduced
the total address space of the machine to 8K, of which 4K is devoted to
RAM, the TIA, and the RIOT registers. This leaves 4K of address space for
cartridge ROM. As Pac-Man demonstrates, limitations in ROM space are
just as signifi cant as limitations in computation time or RAM. A bankswitched
cartridge partly relaxes this constraint, allowing the program to
switch between multiple 4K ROM banks. 11
The Ms. Pac-Man arcade game was itself a variation on Pac-Man, originally
created by General Computing Company as a daughterboard that
attached to the Namco Pac-Man board. The arcade game changed the
appearance and layout of the maze, also adding three new mazes which
appear on successive levels. It also revised the monster AI to make the
behavior of the four opponents less evidently deterministic, changed the
bonus fruit to move and bounce through the maze, and introduced new
cut scenes to go with the fi ction of Pac-Man’s courtship.
The VCS Ms. Pac-Man made considerable use of the additional
ROM space that bank-switching afforded. More ROM made it possible
to have all four mazes in the game. Additional space for sprites
allowed Ms. Pac-Man to face in all four directions, to feature better animation,
and most important, to include game and character logos, bonus
fruits, logos, interstitial screens, and an authentic arcade attract loop
(fi gure 4.3).
Fans and historians sometimes point to Ms. Pac-Man and later VCS
Pac-Man hacks and rebuilds as evidence that Pac-Man could have been a
much better game than it turned out to be. There is, for example, Nukey
Shay’s revision of Frye’s cartridge, which adds credible arcade sounds,
revised colors, better sprite graphics, and colored fruit. 12 Shay also tuned
the speed and control interaction to better match the arcade. The game
includes better renderings of the main eater and of the ghosts, including
animated vertical orientations for Pac-Man. And it replaces the cloying
VCS Pac-Man startup sound with a credible two-voice rendition of Pac-
Man’s characteristic theme music—a remarkable feat, given the lack of
similarity between Atari’s sound registers and the Pac-Man board’s custom
three-channel waveform sound generator.
4 Pac-Man [77]