Amiga Hardware Reference Manual 3rd Edition (1991)

The Amiga operating system is composed of libraries, devices and also resources, all of which provide APIs and data structures for shell commands and Workbench tools to make use of. The foundations on which everything else in the operating system rests are the Multitasking Executive (“exec.library”) and AmigaDOS (“dos.library”).

dos.library itself depends upon exec.library, it is “just” another operating system component after all. You might have expected that AmigaDOS plays a much greater part in the operating system, but the Amiga operating system is not constructed around its DOS component. Almost every Amiga program makes use of exec.library, such as for accessing libraries and devices, but not every Amiga program has need of what dos.library provides. Of course, also libraries and devices can make use of dos.library, such as by opening files on the context of the caller of a library function. Great care must be taken to verify that the caller is indeed a process.

AmigaDOS encompasses dos.library, the CON-Handler, the RAM disk implemented by the RAM- Handler, the default file system and the command line Shell, as well as the shell commands on disk. These components came, mostly, from TRIPOS (Trivially portable operating system) [11] where they were part of a much larger networked multitasking operating system . As one of the last pieces to fall into place in 1985, the components were specially adapted for the Amiga and were not written by the original Amiga and Commodore developers. Both the Amiga operating system and TRIPOS had in common that they were built around non-copying message passing in a shared memory space, which enabled AmigaDOS to work “hand in glove” with the architecture and the means provided by exec.library.

What is known (which is a lot by today) had to be reverse engineered. The classic document everybody references for this is RandyAGA[0].

0. https://github.com/rkrajnc/minimig-mist/blob/master/doc/amig...