The GEMDOS is, apart from the hardware-dependent BIOS and XBIOS, the actual operating system of the Atari and its functions form the highest level of TOS. The functions are called via the 680X0 Trap #1. The operating system functions can be easily divided into categories by the first letter of the function name:
|• File functions||(F...)|
|• Date and Time||(T...)|
|• Process functions||(P...)|
|• Memory management||(M...)|
|• System functions||(S...)|
|• Directory functions||(D...)|
|• Character input/output||(C...)|
Under MagiC, GEMDOS is reentrant (as of MagiC 3.0 this applies even for the file-system!). This is visible, for instance, by alert boxes of the type "Data in Drive A: may be damaged" being movable - because memory has to be demanded for this, which does not work under (Multi)TOS, as a file operation in GEMDOS is being handled at the same time.
With the appearance of MiNT, the GEMDOS was extended by many functions. Also MagiC as of Version 3.0 possesses some MiNT-compatible functions and MetaDOS drivers with corresponding functionality have been spotted.
The GEMDOS receives its parameters on the stack; for this, the last argument from the parameter list is stored as the first on the stack. Function results are returned in processor register d0. Only the registers d3-d7 and a3-a7 are saved, all others will be altered by the call.
See also: XFS-concept in MagiC Background-DMA Program format Function list