Function  55h   "Used Internally by DOS" - Create "Child" PSP 
 *              Create PSP: similar to function 26h (which creates a new Program 
		Segment Prefix at segment in DX) except creates a "child" PSP 
		rather than copying the existing one. 
entry   AH      55h 
	DX      segment number at which to create new PSP. 
return  unknown 
note 1) This call is similar to call 26h which creates a PSP except that unlike 
	call 26h the segment address of the parent process is obtained from the 
	current process ID rather than from the CS value on the stack (from the 
	INT 21h call). DX has the new PSP value and SI contains the value to be 
	placed into PSP:2 (top of memory). 
     2) Function 55 is merely a substitute for function 26h. It will copy the 
	current PSP to the segment address DX with the addition that SI is 
	assumed to hold the new memory top segment. This means that function  
	26h sets SI to the segment found in the current PSP and then calls 
	function 55h.