Int 21H, AH=58H, AL=03H

5 and higher

SET UMB LINK STATE

AH = 58h
AL = subfunction
    03h set UMB link state
	BX = new link state
	    0000h remove UMBs from DOS memory chain
	    0001h add UMBs to DOS memory chain

 CF clear if successful
CF set on error
    AX = error code (01h) (see #01680)		

a program which changes the UMB link state should restore it before terminating

UMBs will only be available if CONFIG.SYS contains the line DOS=UMB, the UMBs have been linked into the memory chain with AX=5803h, and the allocation strategy has been set to include high memory with AX=5801h

#01687,#02766 at INT 2F/AX=4310h

Text based on Ralf Brown Interrupt List Release 61