DOS Plus - Internal Structure

Internal Structure

DOS Plus boots from a single file called DOSPLUS.SYS (rather than the IO.SYS / MSDOS.SYS combination of MS-DOS). This file is in the CP/M-86 CMD format, and is structured internally as a number of modules:

• The BDOS basic disk operating system kernel, which handles multitasking and implements the CP/M API.
• The XIOS extended input/output system, which is the machine-dependent component that performs low-level disc and character I/O.
• The DOS emulator, which converts each MS-DOS function call into one or more CP/M calls. In the case of a request to change the current directory, for example, this would translate to a series of 'open directory' calls, one for each directory in the path.
• A stub which loads COMMAND.COM when required. This stub contains the string "OS=CPCDOS", suggesting that it is based on the Concurrent PC DOS codebase.