INT 21 - COMTROL HOSTESS i/ISA(Industry-Standard Architecture) The expansion bus used by the IBMInternational Busiuness Machines PCIBM PC/ATIBM PC AT. See also EISA. DEBUGGER - GET SEGMENT FOR CONTROL PROGRAM USE ??? Return: AX = first segment available for control program use SeeAlso: INT 20"COMTROL",INT 22"COMTROL"