BetaWiki@BetaWiki

Open encyclopedia of software history. Discord: discord.gg/XPz5Zm42tR

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I worked on MS-DOS, but not this one! Microsoft has open-sourced MS-DOS 4.00 on Github, but it might not be what you think it is. MS-DOS 4.00 was an attempt at a multitasking MS-DOS, but OEMs weren't really interested, and it was only ever in limited release. So it's almost certainly not the one you used back in the day. MS-DOS 4.01, on the other hand, was the one you all know and "love". Actually, it was much maligned. It included the DOSSHELL. People did not love it, as opposed to MS-DOS 5 and 6, which were very well received! More info can be found on Scott Hanselman's site: hanselman.com/blog/open-sour……
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underscor3@underscor31
25 Apr 2024
Windows Longhorn Build 4074, the most widely known (and arguably the most usable) build of Longhorn turns 20 years old today
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To end this thread, one Windows component still shipping today can trace its history directly back to multitasking DOS 4.0 - the Command Prompt. cmd.exe was originally ported from OS/2, which in turn is directly based on the DOS 4.0 COMMAND.COM!
The Windows 11 command prompt.

ALT The Windows 11 command prompt.

A Windows NT 3.1 pre-release command prompt.

ALT A Windows NT 3.1 pre-release command prompt.

The Microsoft OS/2 1.0 command prompt.

ALT The Microsoft OS/2 1.0 command prompt.

The Multitasking MS-DOS 4.0 command prompt.

ALT The Multitasking MS-DOS 4.0 command prompt.
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The design of multitasking DOS 4.0 does in fact share some similarities with OS/2. The DOS kernel exports certain APIs via a NE module called DOSCALLS. The process information structure is the same in both systems. They both also handle errors via a resident hard error daemon.
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Microsoft and IBM later ended up signing the Joint Development Agreement to work on DOS 5.0, the protected mode successor to (multitasking) DOS 4.0. A few renames later, this DOS 5.0 was eventually released as OS/2 1.0.
OS/2 1.0 showing a full screen Program Selector.

ALT OS/2 1.0 showing a full screen Program Selector.

IBM OS/2 box art

ALT IBM OS/2 box art

Microsoft OS/2 box art

ALT Microsoft OS/2 box art

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In the end, most vendors skipped this release. Only a handful of OEMs licensed it. Most of them were based in Europe, therefore this version is sometimes also called the European MS-DOS 4.0.
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Reason #2: IBM. IBM simply wasn't interested in a real mode multitasking OS. They wanted an OS that would take full advantage of the 286 processor. In a market where IBM compatibility was key, this was truly a hard hit.
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Reason #1: Bad backwards compatibility. Multitasking MS-DOS messed with internal structures so much that many apps that didn't fully play by the book, broke. In fact, the devs had to add a compatibility shim to the DOS kernel so Windows could run! learn.microsoft.com/en-gb/ar…

AARDvarks in your code.

learn.microsoft.com
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So why didn't we all end up running Windows on multitasking MS-DOS or XEDOS or whatever? There are two main reasons.
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Of course, aside from NE executables, the system can also run legacy MZ and COM programs. Multitasking MS-DOS still supports and even expands the INT 21h interface. However, the caveat when running legacy programs is that the multitasking is suspended until the program exits.
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In fact, Microsoft at one point planned to release a special version of Windows that integrated with multitasking MS-DOS. Windows 1.0 kernel even calls itself the "Kernel Interface for 2.x and 3.x", implying that a 4.0-compatible kernel was also in development.
Windows 1.0 `KERNEL.EXE` opened in a hex editor, showing a plaintext string "Microsoft Windows Kernel Interface for 2.x and 3.x"

ALT Windows 1.0 `KERNEL.EXE` opened in a hex editor, showing a plaintext string "Microsoft Windows Kernel Interface for 2.x and 3.x"

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Unsurprisingly, multitasking MS-DOS shares tech with Microsoft's other contemporary multitasking environment, Windows 1.0. Both systems natively use the New Executable format. In addition, the Windows memory manager was originally forked from the multitasking MS-DOS one.
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Adding multitasking to MS-DOS was originally the next step towards "XEDOS", a version of DOS virtually identical to single-user XENIX. This process started by DOS 2.0 adding subdirectories and Unix-like file I/O, and later continued with 3.1 adding networking.
Excerpt from the October 1983 issue of BYTE Magazine. Relevant quote: "Microsoft's plans for MS-DOS include gradual upgrades so that single-user MS-DOS will be virtually indistinguishible from single-user Xenix."

ALT Excerpt from the October 1983 issue of BYTE Magazine. Relevant quote: "Microsoft's plans for MS-DOS include gradual upgrades so that single-user MS-DOS will be virtually indistinguishible from single-user Xenix."

A Microsoft advert from InfoWorld vol. 5 no. 26. Relevant section: "The UNIX connection. XENIX is the multi-user, multi-tasking, UNIX-derived operating system for 16-bit microcomputers. MS-DOS 2.0 is Microsoft's single-user OS. MS-DOS and XENIX share hierarchical file structure and I/O redirection, including simple piping. MS-DOS 2.0 also provides XENIX-compatible system calls. That means there's a migration path for programs written to run under MS-DOS and XENIX. What's more, both MS-DOS and XENIX are supported by Microsoft, languages. That's your single-supplier advantage from Microsoft."

ALT A Microsoft advert from InfoWorld vol. 5 no. 26. Relevant section: "The UNIX connection. XENIX is the multi-user, multi-tasking, UNIX-derived operating system for 16-bit microcomputers. MS-DOS 2.0 is Microsoft's single-user OS. MS-DOS and XENIX share hierarchical file structure and I/O redirection, including simple piping. MS-DOS 2.0 also provides XENIX-compatible system calls. That means there's a migration path for programs written to run under MS-DOS and XENIX. What's more, both MS-DOS and XENIX are supported by Microsoft, languages. That's your single-supplier advantage from Microsoft."

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This bad boy can run up to 31 processes on 16 virtual screens on an 8088! Real mode, no memory protection. 640 kilobytes ought to be enough for anybody, literally.
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Did you know? In 1986, Microsoft released a version of MS-DOS which supported preemptive multitasking for compatible applications. This version was called MS-DOS 4.0 and is completely unrelated to the proper, widespread version of MS-DOS 4.0 from 1988!
Multitasking MS-DOS 4.0 showing a "Switch" popup with "COMMAND", "FDISK", "DISKCOPY" and "Start a program" options.

ALT Multitasking MS-DOS 4.0 showing a "Switch" popup with "COMMAND", "FDISK", "DISKCOPY" and "Start a program" options.

Multitasking MS-DOS 4.0 showing the output of the command `ps -lp` with multiple processes running on the machine.

ALT Multitasking MS-DOS 4.0 showing the output of the command `ps -lp` with multiple processes running on the machine.

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RT @luciascarlet: @dm4uz3 why is this how I find out MS-DOS is open-source
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look between B and W on your keyboard
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Credit goes to @jeffpar for sharing this build, and to @hyenaskyy, @substanc3dev and others for working hard to make this obscure build work in an emulator!
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"Just say WOW!" Presenting the Windows NT "WOW Reversi MIPS Demo", currently the earliest available NT build. This build was compiled in early April 1991 as an early demonstration of Win16 apps running under emulation on a non-x86 machine.
"Reversi" from Windows 3.0 running on an early build of Windows NT from April 1991. The pieces are square rather than round, because the graphics subsystem (GDI) is so early that it didn't support drawing circles yet.

ALT "Reversi" from Windows 3.0 running on an early build of Windows NT from April 1991. The pieces are square rather than round, because the graphics subsystem (GDI) is so early that it didn't support drawing circles yet.

The x86 emulator console and output windows.

ALT The x86 emulator console and output windows.

A dialog box captioned "WOW!", that says "Just say WOW! This 16-bit x86 Windows app brought to you by the MVDM Team"

ALT A dialog box captioned "WOW!", that says "Just say WOW! This 16-bit x86 Windows app brought to you by the MVDM Team"

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Geoff Chappell passed away today on his own terms, surrounded by family and while his good humor remained intact. Please listen to a Beatles record and read a little assembly code in his honor.
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