2158 INT 21 - DOS 2.11+ - GET OR SET MEMORY ALLOCATION STRATEGY 2158 INT 21 - DOS 5+ - GET OR SET UMB LINK STATE 2158CC INT 21 - VIRUS - "1067"/"Headcrash" - INSTALLATION CHECK 2158DD INT 21 - VIRUS - "1067"/"Headcrash" - GET ORIGINAL INT 21h VECTOR