The Atari 815 was Atari, Inc's first and only true double density disk drives.   The 815 utilitized both MPI and Tandon mechanisms and had both versions of the front plastic panels to support either drive.    The 815's are huge to say the least, almost as tall as 2 810's stack one atop another.    The 815's had built in power supplies and could support drive assignments as follows: 1&2 or 3&4 or 5&6  or 7&8.     The 815's sold for $1,500.00 and were sold in very limited quantities.   Only a small handful of Atari catalogs ever displayed the Atari 815 in them.   Atari also sold a special version of Atari DOS 2.0 with a "d" designation for double density, all other Atari DOS 2.0's were 2.0s versions.   Paul Mancuso and Levon Mitchell were the designers of the fabled 815.   Levon was not happy that the project had been canceled, and that is more then understandable considering the time and effort that was placed into such a project.   As Paul Mancuso had explained:   "Roger Baderscher while deciding whether to Ok the project for full production or cancel it in discussions with Levon put him on the spot and requested that he demonstrate whether the units were fully Atari 810 disk drive compatible."   This feature had no yet been fully ironed out in the Pilot run of 60 units and unfortunately the demonstration did not convince Roger to keep the project going, so it was cancelled.   AHS member Christopher Strong is one of our resident Atari History experts on the Atari 815, owning over half a dozen units.