The idea to bring back Ms Pac-Man came from Ed Pellegrini who owns half of Atlas Distributing, a major coin-op distributor. He noticed that almost 20 years later operators still wanted Ms Pac-Man games. So, why not make new ones? Namco, the company that created and owns Ms Pac-Man, is one of Atlas' many lines, so Ed worked his way up the chain to get the necessary approvals. Namco liked the idea so much that they wanted to sell it themselves.
The engineering challenge was straight-forward: design an inexpensive new circuit board using currently available components to run Ms Pac-Man exactly as it ran in 1981. About two months into the project we were asked if it could run Galaga as well. Galaga has three Z80 processors where Ms Pac-Man has one, Galaga has 64 sprites where Ms Pac-Man has six, Galaga's stamps are in front of the sprites while Ms Pac-Man's are behind, not to mention the additional complexity of switching between games in the attract mode and selecting which game to play. At least the sound hardware is pretty much the same. Suddenly it wasn't such a simple design task.
To make matters worse we would need to make some minor tweaks to the game code to enable the games to live together on the same hardware and Namco was unable to come up with the source code. So, we wound up disassembling and reverse-engineering pretty much all of both games.
The final hardware is something of a cross between the two. It has 64 sprites, so Ms. Pac-Man simply skips 58 of them. It has a 20 MHz Z180 which is more or less code compatible with the Z80; it emulates the three processors on Galaga by calling their main loops in sequence. It can turn on or off the starfield (so it's possible to have a starfield running behind Ms Pac-Man, which is sort of interesting) and it can put the sprites either in front of or behind the stamps.
Very near the end of the development cycle Namco asked if we could tuck Pac-Man in, also. If at the game select screen you move the joystick up three times, then down three times, then left-right-left-right-left you'll hear the Pac-Man 1UP sound and the ghost will turn from red to pink. If you then press Ms Pac-Man start the game will play Pac-Man instead.
The "Classic Reunion" name was Don Marshall's idea. Don's company created the cabinet art and all the flyers. Don is also our landlord and downstairs neighbor. The first flyer was like a class reunion with Ms Pac-Man voted "Most Likely to Succeed" and Galaga voted "Class Space Case". The beat-up original games on the flyer are from Cosmodog's classic arcade game collection (most of our other games are in better shape).
Namco's Ms Pac-Man / Galaga page: http://www.namcoarcade.com/nai_gamedisplay.asp?gam=mspcglga