Interrupt 21h
Function  4Ah   Modify Allocated Memory Blocks (SETBLOCK)
		Expand or shrink memory for a program
entry   AH      4AH 
	BX      new size in 16 byte paragraphs 
	ES      segment address of block to change 
return  CF      clear   nothing 
		set     AX      error code (7, 8, 9) 
		    or  BX      max number paragraphs available 
note 1) Max number paragraphs availible is returned only if the call fails 
     2) Memory can be expanded only if there is memory availible