IBM PC-DOS 0.90

"0.90" or 86-DOS 1.05 is a pre-release version of PC-DOS 1.00. This is actually 86-DOS 1.05, as PC-DOS 1.x was essentially 86-DOS but updated for the IBM PC platform. (the final PC-DOS being 1.14, and 1.1 being 1.25).

This is dated 1981-06-04 and is roughly halfway through conversion - this build was the first one where the disk format had just been changed to the final IBM PC 8-track 160/320K disk format.

There are significant differences in this version when compared to DOS 1.x - EXE file support is nonexistent, there are versions of Disk and Advanced BASIC that do not require the IBM PC BASIC ROMs (bas18 and bas18a), and the BASIC examples are completely different.