This appears to be a 2nd
revision of the Atari 1200XL design, not an early design. It may have
also been a possible design concept for the 1400XL computer. The Atari
1200XL was shown to the public in December 1982 and began manufacturing
Domestically in the US with shipments starting in February 1983. In
March of 1983 the specifications for the Atari 600XL and shortly
afterwards the 800XL were written up. By June of 1983 the specifications
for the Atari 1400XL and 1450XLD were also written up. By July of 1983
the Atari 1200XL was discontinued with the expectation that by fall of
1983 the "New" XL's would be taking it's place, all with expansion
capabilities and other features.

The left side of this 2nd
revision 1200XL lacks the side cartridge slot and instead has it relocated
to the top of the chassis in the same fashion that the 600XL and 800XL
computers were designed. The joystick ports are flush and not at a right
angle, this would be carried over into the 1400XL and 1450XLD computers as
well. Only a side on/off switch is still located in the same position.
The 45 degree joystick ports, while being actually very convenient for the
end users and adding a nice style to the case design, caused difficulties
during assembly and placement of the main board into the lower half of the
case, so they were eliminated in future model designs.

The rear of the case is
where the idea that this may have been a concept idea for an early
1400XL design. Using the same cartridge placement as the 600XL and
800XL computers. It is possible that Atari designers may have, shortly,
contemplated doing the same for the 1400XL design. The rear of the
system is very close the layout of the product designed 1400XL
computer. On the expansion bay opening hasn't been finalized. It would
appear in this mock up, that Atari designers were going to consider
using some kind of "keyed" plug in expansion cable.
Are you a former Atari
engineer? Did you have any involvement or direct knowledge of this
project? If so, please contact the Atari Museum:
CLICK HERE