Multicarts

NeoGeo multicarts are bootleg compilation cartridges, mostly (all ?) of the arcade type, often containing dozens of games which can be chosen from a video menu.

Many of these contain multiple versions or hacks of a given game, as it can be seen on the usually provided list.

See http://wiki.arcadeotaku.com/w/MVS_Multicart

Brute force method

The first multicarts worked with a complex add-on board which had to be connected to the system's JAMMA connector and the cartridge itself via a ribbon cable.

The board had mechanical relays (on the +5V and +12V lines) to control power to the MVS board, and a large LPC2214 microcontroller to generate the menu display itself.

When a selection is made, the game code is presented to the cartridge as a binary word by the ribbon cable, the MCU stops generating video and the MVS board is powered up.

Changing games requires the user to press a combination of buttons, making the add-on board cut the power and display the menu again.

Software method

A few years later, "real software" menus were made and embedded in the cartridge to run on the MVS board itself, making everything simpler and cheaper.