Although the Atari 5200's internal design was extensively based on that of the 400/800 home computers, the differences were sufficient that games designed for one would not run directly on the other.
One of the most obvious differences was the 5200's lack of a keyboard. However, there were several others:
The 400/800's 10 KB operating system was replaced with a simpler 2 KB BIOS, of which 1 KB is the built-in character set.
A number of important registers, such as those of the GTIA and POKEY chips appear at different memory locations.
The purpose of some registers changed slightly on the 5200.
The 5200's analog joysticks required different input handling to the traditional digital joystick input on the 400/800. (However, the 5200 reassigned/rewired two of the 400/800's existing analog paddle registers for each bi-directional analog joystick input).
Atari Corp.'s later XE Games System revisited the idea of a console based on the 400/800 hardware. However, as this was essentially just a 65XE computer with a detachable keyboard, it was able to run most of the home computer titles directly.
 Market Performance
The Atari 5200 did not fare well commercially, compared to its predecessor, the Atari 2600. While it touted superior graphics to the 2600 and Mattel's Intellivision, the system was initially incompatible with the 2600's expansive library of games, and some market analysts have speculated that this hurt its sales especially since an Atari 2600 cartridge adapter had been released for the Intellivision II. (A revised 2-port model was released in 1983, along with a game adapter that allowed gamers to play all 2600 games.) This lack of new games was due in part to a lack of funding, with Atari continuing to develop most of its games for the saturated 2600 market.
Many of the 5200's games appeared simply as updated versions of 2600 titles, which failed to excite consumers. Its pack-in game, Super Breakout, was particularly criticized for not doing enough to demonstrate the system's capabilities, and this gave the ColecoVision a significant advantage when its pack-in, Donkey Kong, delivered a more authentic arcade experience than any previous game cartridge. In its list of the top 25 game consoles of all time, IGN claimed that the main reason for the 5200's market failure was the technological superiority of its competitor, while other sources maintain that the two consoles are roughly equivalent in power.
At one point following the 5200's release, Atari had planned a smaller, cost-reduced version of the Atari 5200, which would have removed the controller storage bin. Code-named the "Atari 5100" (a.k.a. "Atari 5200 Jr."), only a few fully working prototype 5100s were made before the project was canceled.
On May 21, 1984, during a press conference at which the Atari 7800 was introduced, company executives revealed that the 5200 had been discontinued after just two years on the market. Total sales of the 5200 were reportedly in excess of 1 million units.
 Technical specifications