The Atari 815 was Atari, Inc's first and only true DS/DD disk drive.   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.   The Atari 815's were too complex for assembly systems at the time and had to be hand built which took several man-hours and cut the profit of these units to next to nothing, so it was decided to pull the plug on the Atari 815 and take it out of production just as production had started.