used to distinguish between the multitasking MS-DOS 4.x and the later MS-DOS/PC DOS 4.x issues. Microsoft president Jon Shirley described it as a "specialized version" and went as far as saying "maybe we shouldn't have called it DOS 4.0", although it's not clear whether this was always the intention, or if a more enthusiastic response from OEMs would have resulted in it being the true successor to DOS 3.x. The marketing positioned it as an additional option between DOS 3.x for workstations, and Xenix for higher-end servers and multiuser systems. External commands MS-DOS Version 4.10.20 supports the following external commands: APPEND ASSIGN ATTRIB BACKUP CHKDSK COMMAND DEBUG DETACH DISKCOMP DISKCOPY EDLIN EXE2BIN FC FDISK FIND FORMAT GRAFTABL GRAPHICS GWBASIC HEADPARK INSTALLX JOIN LABEL LINK4 MODE MORE MOUS PERM0 PRINT QUEUER RECOVER REPLACE RESTORE SETUP SHARE SORT SUBST SYS TREE XCOPY See also Concurrent DOS, Concurrent DOS 286, Concurrent DOS 386 - Concurrent CP/M-based multiuser multitasking OS with DOS emulator since 1983 DOS Plus - Concurrent PC DOS-based multitasking OS with DOS emulator since 1985 DoubleDOS - enabled limited multitasking by partitioning a PC into two simultaneous DOS sessions Novell DOS, OpenDOS, DR-DOS - successors of DOS Plus with preemptive multitasking in VDMs since 1993 FlexOS - successor of Concurrent DOS 286 since 1986 4680 OS, 4690 OS - successors of FlexOS 286 and FlexOS 386 since 1986 Multiuser DOS - successor of Concurrent DOS 386 since 1991 REAL/32 - successor of Multiuser DOS since 1995 PC-MOS/386 - multiuser multitasking DOS clone since 1987 VM/386 - multiuser multitasking DOS environment since 1987 TopView - DOS-based multitasking environment since 1985 DESQview, DESQview/X - DOS-based multitasking environment since 1985 Virtual DOS machine Datapac Australasia References Further reading 1986 software Discontinued Microsoft operating systems Disk operating systems DOS variants Proprietary operating systems Assembly language software