The true successor to the Atari 2600. Releasing three times, once in June 1984, twice in January 1986, and lastly in May 1986, the Atari 7800 was able to hold it's own position in the market, but was still quite unsuccessful despite somehow achieving 2nd place (over SEGA). Containing a 6502C based CPU, 4 KB of RAM, and being able to output up to 320×240, the 7800 was not a powerhouse but did not lag behind the times. Sales figures are rough, but it appears to have sold at least 1 million units.

https://en.wikipedia.org/wiki/Atari_7800

GeckOS is advertised as an extremely easy OS to port to alternative 6502 platforms

As of now, this is ONLY a theoretical port. GeckOS itself is a 6502-based OS with a highly portable nature, which means it could absolutely end up here at some point.

https://lobste.rs/s/xzfgrr/geckos_unix_like_6502_operating_system

http://www.6502.org/users/andre/osa/index.html

https://github.com/fachat/GeckOS-V2

https://en.wikipedia.org/wiki/GeckOS

For general information, see the Game Console Revisions Overview.

There are two versions of this console, arranged chronologically.

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The original run of the 7800, which had to cease production later that year due to contractual disputes. Sold only in southern California at first. Upon the 1986 relaunch, all overstock from the 1984 run was sold, but it is unknown if sales were still limited to California or not. The only noteworthy difference to the later run, is the presence of an unused expansion port on the left side.

Identical to the 1984 run 7800, except the expansion port is now gone.

There are two revisions within the 7800 (1986-1992), and no revisions within the 7800 (1984).

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Outside of a minor motherboard change, this Atari 7800 version has no expansion port anymore. However, there is an indent located where the port used to be. This version may have a minor incompatibility with “Dark Chambers”, a 2600 game.

The exact same as above, except either a small outline or nothing at all replaces the expansion port indent. Aforementioned “Dark Chambers” defect may not exist, however, games using FE-bank switching may be incompatible instead (Centipede, Kool-Aid Man, etc.)

BEST RELIABILITY couldn’t be assigned.

https://en.wikipedia.org/wiki/Atari_7800#System_revisions

http://www.ataricompendium.com/game_library/easter_eggs/7800/78prosystem.html