The module structure requires more explanation: OS-9 keeps a "module directory", a memory-resident list of all modules that are in memory either by having been loaded, or by having been found in ROM during an initial scan at boot time. When one types a command to the OS-9 shell, it will look first in the current module directory for a module of the specified name and will use it (and increase its link count) if found, or it will look on disk for an appropriately named file if not. In OS-9/6809 and OS-9/68000, the module directory is flat, but OS-9000 made the module directory tree-structured. The OS-9000 shell looks in one's alternative module directory for a MODPATH environment variable, analogous to the PATH variable in all versions, indicating the sequence of module directories in which to look for pre-loaded modules.
the module structure requires more explanation os-9 keeps a "module directory" a memory-resident list of all modules that are in memory either by having been loaded or by having been found in rom during an initial scan at boot time when one types a command to the os-9 shell it will look first in the current module directory for a module of the specified name and will use it (and increase its link count) if found or it will look on disk for an appropriately named file if not in os-9/6809 and os-9/68000 the module directory is flat but os-9000 made the module directory tree-structured the os-9000 shell looks in one's alternative module directory for a modpath environment variable analogous to the path variable in all versions indicating the sequence of module directories in which to look for pre-loaded modules