Saturn

Sega made sure to retain compatibility with most Saturn accessories. There are a few notable differences though, such as-

-The “Cartridge slot” is utilized for SCSI communication with the rest of the Prologue. This means save cartridges, 1M/4M RAM carts, ROM carts, and cheat cartridges are not compatible with the Prologue 21 as there is no slot present to use them.

-The VCD connector is either inaccessible or not populated depending on model, VCD cards cannot be installed in the system for the couple games that utilize the function.

-The serial port is not present to use for the Link Cable, FDD, Printer, or MIDI hardware that makes use of it.

-Most Prologues do not have a CR2032 battery or holder populated on the motherboard. As such, games will not save through a power off cycle. Some very early units do have the holder populated, but is buried inside the system and extremely difficult to access.

-RGB output has been removed. Composite and S-Video are the only video output options as built.

Aside from these caveats, the Prologue 21 is compatible with Saturn controllers and Japanese software, and should work with nearly all of the Japanese library. I have seen anecdotes of gamers playing Virtual On using the Prologue 21 in a karaoke booth within the week of the game’s release. I can only imagine if they did so using the Twin Stick controller.