This may be interesting, “PC DOS 1.1 From Scratch” by Michal Necasek (OS/2 Museum). Especially for anyone interested in / fighting with the tool chains of the day…
A number of years ago, the Computer History Museum together with Microsoft released the source code for MS-DOS 1.25 (very close to PC DOS 1.1) and MS-DOS 2.11. I never did anything with it beyond glancing at the code, in no small part because the release was rather poorly organized.
Now I finally decided to look at the code for DOS 1.1 and see how far I could get with it. For both DOS 1.1 and 2.0, there are ‘object’ and ‘source’ directories.
(…)
I was able to put together a bootable 320K floppy running something very close to PC DOS 1.1 with source code and tools that allow rebuilding IBMBIO.COM, IBMDOS.COM, and COMMAND.COM. Batch files (MKBIO.BAT, MKDOS.BAT, MKCOM.BAT) are provided to simplify the effort. Everything is done “in place” with very little room left on the disk.
See also this previous post on OS/2 Museum regarding the original PC-86-DOS, the precursor to PC-DOS 1.x, by SCP and efforts to run it on real hardware using an early version of IBMDOS.COM.
(SCP’s version of DOS did not rely on the boot sector format known from PC-DOS, but rather reserved the entirety of the first two tracks, 52 sectors, for boot loading, which is, where the real difficulties arise.)
The first two tracks is where CP/M stored it’s command processor and such. And PC-86-DOS was originally written to be a stop-gap CP/M-86 to test out hardware.