DOS Plus - Commands

Commands

DOS Plus contains a number of extra commands to support its multitasking features:

• ADDMEM: Sets the amount of extra memory to allocate to EXE programs.
• ALARM: A message alarm clock.
• BACKG: Allows background processes to be listed and stopped.
• COMSIZE: Sets the amount of memory to allocate to COM programs.
• PRINT: Print spooler.
• SLICE: Sets the amount of processor time to give to the foreground program.
• USER: Sets the user number to use when accessing CP/M media.

It also contains subsets of the standard DOS commands and CP/M commands - for example, it has both a built-in COPY command, and a PIP utility, both of which copy files.

The CD command can assign one of the three drives N:, O: or P: to a directory on a different drive, in a similar manner to the MS-DOS command SUBST. For example,

will cause the directory C:\DATA\ACCOUNTS to appear as drive N:. This so called floating drive feature allows old programs which don't support subdirectories to work under DOS Plus and can be used to make file handling at the command prompt much easier. This feature is also present in Concurrent DOS, Multiuser DOS, System Manager 7, and REAL/32, however, these systems extent the concept to all unused drive letters from A: to Z:, except for drive letter L:. DR DOS 3.31 - 6.0 (up to the 1992-11 updates with BDOS 6.7 only) also support this (including drive letter L:). Under the later systems, the 4DOS/NDOS command processor supports this features as well. Interestingly, floating drives are implemented in the BDOS kernel, not in the command line shell, thus this feature can also be used from within DOS applications when entering directory paths for as long as the application does not parse and split the dirspec for further processing.

Using a similar feature, Concurrent DOS, Multiuser DOS, System Manager and REAL/32 will dynamically assign a floating drive L: to the load path of a loaded application, thereby allowing applications to refer to files residing in their load directory under a standardized drive letter instead of under a fixed absolute path. This load drive feature makes it much easier to move software installations on and across disks without having to adapt paths to overlays, configuration files or user data stored in the load directory or subsequent directories. (For similar reasons, the appendage to the environment block associated with loaded applications under MS-DOS/PC DOS 3.0 (and higher) contains a reference to the load path of the executable, however, this consumes more resident memory, and to take advantage of it, support for it must be coded into the executable, whereas DRI's solutions transparently works with any kind of applications.)

Another interesting feature resulting from the BDOS' internal organization of current working directories as relative links to parent directories is the theoretically unlimited directory depth supported by all those above mentioned operating systems - in contrast to MS-DOS/PC DOS (and DR DOS since 1992), where an MS-DOS compatible internal data structure named Current Directory Structure (CDS) limits directory depths to a maximum of 66 characters.

These features can be contributed to the fact, that CP/M itself did not have a concept of subdirectories and DOS was only some kind of emulation under these operating systems, so directories had to be translated to internal CP/M structures in some intelligent way.