Inside, the unit's CPU is a 68LC040 processor and there is also a dedicated MPEG decoder chip. The unit has its ROM stored on a separate removable card, and also has slots for an expansion card and RAM.
These are pretty rare devices, and would be a good items for a serious Apple collectors. The item "(2x) RARE Vintage Apple Interactive Television M4120 Set Top Box (STB) Prototype" is in sale since Monday, November 13, 2017. This item is in the category "Computers/Tablets & Networking\Vintage Computing\Vintage Computers & Mainframes".
The seller is "echoinie" and is located in Rumford, Rhode Island. This item can be shipped worldwide.