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Multitasking MS-DOS 4.00

These disk images contain the first unearthed copy of Microsoft’s “multitasking” version of MS-DOS since its extremely limited release around late 1985 or early 1986. They were were discovered by the PCjs Project in March 2013. More information is available at Wikipedia, OS/2 Museum, and MSDN Blogs.

Note: The designation “4.0M” is not an official version number; it’s an internal version number used only to differentiate these disk images from those of the official MS-DOS 4.00 release in October 1988.

The IBM Model 5160 machine configuration below boots MS-DOS 4.0M. To access the MS-DOS “Session Manager” after it’s booted, tap the Alt key. Since the Alt key is not available in all browsers, you may need to click the “Keys” button and use the Alt key on the on-screen keyboard.

[PCjs Machine "ibm5160"]

Waiting for machine "ibm5160" to load....

Additional Information

Courtesy of PC DOS Retro:

Multitasking MS-DOS 4.0 was a little known and separate development of DOS done in parallel with the development of DOS 3.0 and 3.1 and was released in late 1985. It should not be confused with the later retail DOS 4.0 that was released in 1988.

DOS 4.0 supported preemptive multitasking, shared memory, semaphores, advanced memory management, a session manager, imports, exports and a new executable format. Many of the ideas and features introduced here found their way into OS/2. Unfortunately DOS 4.0 was limited by the real-mode 8086 environment and the 640KB address space. Also programs which were not well-behaved or relied upon undocumented DOS functions would not run properly under DOS 4.0, particularly TSR programs.

Despite these limitations Microsoft wanted to make DOS 4.0 a retail product but IBM at the time was not interested in such a version of DOS, instead they formed a joint development agreement with Microsoft which resulted in the development of OS/2 1.0. Microsoft licensed DOS 4.0 to several European OEMs including Goupil but it was never shipped in North America. Microsoft released an updated version, DOS 4.1 in late 1987 for the British company International Computers Limited (ICL). DOS 4.1 incorporated features from DOS 3.2. Like its predecessor, DOS 4.1 was never shipped in North America.

List of features and differences between standard DOS and Multitasking MS-DOS 4.0:

Directory of MS-DOS 4.0M (Disk 1)

 Volume in drive A has no label
 Directory of A:\

IBMBIO   COM*    23962  11-26-85  10:49p
IBMDOS   COM*    62080  11-26-85  10:49p
COMMAND  COM     37488  11-26-85  10:49p
HE_DAEM  EXE      3580  11-26-85  10:49p
POPUP    EXE      1870  11-26-85  11:04p
ANSI     SYS      2535  11-26-85  10:49p
RAMDRIVE SYS      6466  11-26-85  10:49p
POPUP    PIF       369   9-20-85   2:28p
HE_DAEM  PIF       369   9-20-85   2:27p
COM      SYS      2325  11-26-85  10:49p
EGA      SYS      7599  11-26-85  10:49p
CONFIG   SYS        58   3-10-13  12:07a
AUTOEXEC BAT        62   3-10-13  12:01a
BIN          <DIR>       3-10-13  12:08a
README   TXT        62   3-08-18  12:01a
       15 file(s)     148825 bytes

 Directory of A:\BIN

.            <DIR>       3-10-13  12:08a
..           <DIR>       3-10-13  12:08a
ASSIGN   EXE      5344  11-26-85  11:03p
CHKDSK   EXE      9280  11-26-85  11:03p
COMMAND  COM     37488   2-24-86  11:42a
DISKCOPY PIF       369   7-15-85   9:28p
DISKCOPY EXE      4504  11-26-85  11:03p
FDISK    EXE     16294  11-26-85  11:03p
FORMAT   EXE      8897  11-26-85  11:57a
JOIN     EXE      9060  11-26-85  11:04p
MODE     EXE     11554  11-26-85  11:04p
SM       EXE      5700  11-26-85  11:04p
SM       PIF       369   9-11-85  10:26a
SUBST    EXE      8400  11-26-85  11:05p
SWAPPER  DOC      1247  11-26-85  12:31p
SWAPPER  EXE      2816  11-26-85  10:49p
SWAPPER  PIF       369   9-20-85   2:28p
SYS      EXE      3693  11-26-85  11:55a
       18 file(s)     125384 bytes

Total files listed:
       33 file(s)     274209 bytes
                       69632 bytes free

Directory of MS-DOS 4.0M (Disk 2)

 Volume in drive A has no label
 Directory of A:\

APPEND   EXE      2508  11-26-85  11:03p
ATTRIB   EXE      6410  11-26-85  11:03p
BACKUP   EXE     21304  11-26-85  11:03p
EDLIN    EXE      7044  11-26-85  11:03p
FC       EXE      2585  11-26-85  11:03p
FIND     EXE      6363  11-26-85  11:03p
KEYBFR   EXE      2846  11-26-85  11:04p
KEYBGR   EXE      2838  11-26-85  11:04p
KEYBUK   EXE      2784  11-26-85  11:04p
KEYBIT   EXE      2790  11-26-85  11:04p
KEYBSP   EXE      2881  11-26-85  11:04p
KEYBDV   EXE      2784   9-27-85   8:35a
LABEL    EXE      9830  11-26-85  11:04p
LINK4    EXE     52604  11-26-85  11:04p
MORE     EXE       938  11-26-85  11:04p
PIFEDIT  EXE     32366  11-26-85  11:04p
PRINT    EXE      9444  11-26-85  11:04p
QUEUER   EXE      6312  11-26-85  11:04p
RECOVER  EXE      3953  11-26-85  11:04p
RESTORE  EXE     19756  11-26-85  11:04p
SORT     EXE      1632  11-26-85  11:05p
       21 file(s)     199972 bytes
                      153600 bytes free

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