"The Atari 7800 ProSystem, or simply the Atari 7800, is a video game console re-released by Atari Corporation in January 1986. The original release had occurred two years earlier under Atari Inc. The 7800 was designed to replace Atari Inc.'s unsuccessful Atari 5200 and later to re-establish Atari Corp.'s market supremacy against Nintendo and Sega. With this system, Atari Inc. addressed all the shortcomings of the Atari 5200: it had simple digital joysticks; it was almost fully backward-compatible with the Atari 2600; and it was affordable (originally priced at US$140).

The Atari 7800 could play almost all Atari 2600 games out of the box.

Source: Wikipedia, "Atari 7800", available under the CC-BY-SA License.