The DosStartSession() function under OS/2 Version 2.0 provides an environment pointer as one of its parameters. This pointer references a buffer which is used when creating a VDM. This buffer contains the buffer length, followed by one or more DOS settings. For each setting, the buffer specifies the type, name and value. The operating system parses the settings buffer as part of the DosStartSession() processing, in order to create initial values for these settings. Default values are assumed for any registered settings not specified in the DosStartSession() call.
For any settings which have not been registered, the information in the buffer is ignored. This allows the system to run without errors in the case where the virtual device driver that registered a setting is not loaded (for example, CONFIG.SYS was changed), and yet the Presentation Manager shell has saved a value for that setting.