A NeoGeo multicart is an unofficial compilation cartridge, containing a selection of games. Most of them are of the arcade type but some can be played on the home console by using an MVS to AES adapter. The 161-in-1 Series 1 has been converted to home cart format.
Many of these contain multiple versions or hacks of a given game, as it can be seen on the usually provided list.
Brute force method
Early multicarts worked in pair 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 has 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 via 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 to the MVS board and display the menu again.
A few years later, menus running on the MVS hardware itself were made and embedded in the cartridge's memory, making everything simpler and cheaper.
The game bank is set by the software through custom registers mapped in the second cartridge zone, which are implemented in large CPLDs.