There were several models of the odyssey, many were similar. Odyssey 1 and 2 took cartridges, the 100, 200, 300, 400, 500, 2000, 3000, and 4000 series were pong clones. The 100, 200, 300, etc. came later than the Odyssey 1 and 2. The 100 and up were all pretty much the same, each subsequent model got a little more complex, such as adding difficulty levels and more game variations.