QDOS was created because sales of SCP's 8086 computer kit, demonstrated in June 1979 and shipping in November, were languishing due to the absence of an operating system.
QDOS met IBM's main criteria: It looked like CP/M, and it was easy to adapt existing 8-bit CP/M programs to run under it, notably thanks to QDOS's TRANS command which would translate source files from 8080 to 8086 machine instructions.
