QDOS 0.10

QDOS 0.10 is the first beta build of QDOS/86-DOS. It was in a roughly half-complete state when compiled. An estimate of only 10 people have ever seen it, and it was never shipped.

Features
QDOS 0.10 was a preliminary release, including a very limited number of commands crammed into 6 KB of object code.

Disk
QDOS 0.10 used a modified version of BASIC-86's FAT file system, chosen because of the small cluster sizes, speed, and error handling capabilities. The modifications included supporting 12-bit table elements (allowing for 64MB disks), reducing the number of FATs from 3 to 2, and using 16-byte directory entries. The filesystem was additionally adapted to allow for CP/M (8.3) filenames, though a date field was not included as QDOS didn't support date stamps.

QDOS also added file control blocks from CP/M as well.

Commands
QDOS's commands were split into internal and external commands. External commands were .COM files in the root directory, while internal commands were not visible.

While not counted as a command in the later version 0.3 manual, it should also be noted that QDOS had the ability to run executable files by inputting their filenames.

Program Segment Prefix
QDOS 0.10 created the Program Segment Prefix (PSP), a 256-byte data structure used to store program states. It takes clear inspiration from CP/M-80's Zero Page, using a similar far call entry and exit.