Commodore MAX Machine (also know as Commodore Ultimax) was a game console based on the sound and video chips of the famous Commodore 64 8-bit computer. It was released only in Japan, where it sold very poorly. The most probable reason for its market failure was that it cost about the same as the VIC-20 computer, while lacking any substantial software library and using an almost unusable membrane keyboard. The machine could not survive in a competitive Japanese market, and only a limited number of machines were produced. Due to their rarity, MAX Machine consoles are regarded as collector items and sell for at least $500-$700 on online auctions.
However, the MAX Machine legacy lives in millions of Commodore 64′s and 128′s sold worldwide. Because the console used the same chips as Commodore 64 and Commodore wanted to reuse existing game cartridges when introducing the 64, they built in a (somewhat limited) compatibility mode into the home computer, allowing it to use the software written for the MAX Machine. This mode was also carried onto Commodore 128, which has a Commodore 64 compatibility mode and thus can also use MAX Machine cartridges.
In this mode the Commodore 64 memory map is changed significantly to resemble the MAX Machine. This allows all kinds of interesting hacks for Commodore 64, including “freezer” cartridges such as Final and Action Replay, as well as modern kernal replacement cartridge EasyFlash. Thanks to this, you can also use the MultiMax cartridge on your Commodore 64 and 128.
If you are interested in the MAX Machine, here is some more information:
Explains similarities and differences between the MAX Machine console and the home computer.