From Pong-Story.com:  Philips also released two interesting systems which didn't have US equivalents: the Odyssey 2001 in 1977 and the Odyssey 2100 in 1978. They were sold in several countries like Germany, Belgium and Switzerland. Their case was nearly same as the one of the Odyssey 4000. The controllers were same except that the sticks were replaced by knobs. As a matter of fact, they used dedicated chips made by NS (the MM-57105 for the Odyssey 2001, and the MM-57186 for the Odyssey 2100), which only allowed moving the players vertically. The Odyssey 2001 played three games in color, and the Odyssey 2100 played six different types of games with several variants for each type, making a total of 23 games. The game selection was done by pushing the button of one of the controllers (the button of the other controller reset the games). Amazingly, the electronic circuit board occupies a sixth of the space available in the systems cases.