Int 2F Fn 270B  - Dr Dos 6.0 Taskmax - Convert Task Id To Task Index       [T]

   AX = 270Bh
   DX = task ID

Return: DX = task index (FFFFh if task not active)

Note:  the TaskMAX API is also supported by Novell DOS 7 TASKMGR in both
     taskswitching and multitasking modes

See Also: AX=270Ah