INT 2F - DOS v5.0 TASK SWITCHER - ALLOCATE SWITCHER ID
AX = 4B03h
ES:DI -> task switcher entry point (see AX=4B02h)
Return: AX = 0000h
BX = switcher ID (0001h-000Fh), or 0000h if no more available
Notes:  if a task switcher has determined that it is the first to be loaded, it
must allocate an identifier for itself and provide this function to
all subsequent task switchers; if it is not the first to be loaded,
it must call this function to allocate an ID.  The switcher ID is
used as the high four bits of all session identifiers to ensure
unique session IDs.
if no more switcher IDs are available, the new task switcher making the
call must terminate or disable itself
the task switcher providing the identifiers may call the new task
switcher's entry point as needed
this call is available from within DOSSHELL even if the task switcher
is not installed
SeeAlso: AX=4B04h

See also: 2F4B02

2F4B03 - DOS v5.0 TASK SWITCHER - ALLOCATE SWITCHER ID