Newly open-sourced MS-DOS 4 installed on an IBM Personal System/2 with a 16 MHz Intel 386 CPU — took 70 minutes to build

Photo of an IBM PS/2, mid-MS-DOS 4 install. (Image credit: @VirtuallyFun on Twitter)

Following last week's open sourcing of MS-DOS 4 and critique, Twitter user VirtuallyFun shared their cutting-edge 16 MHz Intel i386 MS-DOS 4 install on the 1987 IBM Personal System/2, which mainly lives on today in its legacy PS/2 peripheral connectors. In its time, the IBM PS/2 could also have been paired with IBM's PC DOS or Microsoft-collab Operating System/2.

This MS-DOS 4 install wasn't done with the main Microsoft GitHub repo but instead VirtuallyFun's own dos400 branch. Dos400 forces the 4.0 version of MS-DOS and patches out issues like a bug in msload.asm that prevented booting from the hard drive. This bug was diagnosed by Michal Necasek, who readers of the previous story will recognize as the owner of OS/2 Museum and noted critic of the initial MS-DOS 4 release.

With bugs fixed through his own GitHub branch, Virtually Fun was able to share a full video demonstrating MS-DOS 4 compilation using DOSBox and Qemu. The video is seventeen minutes long and includes ongoing commentary on exact workarounds being used and bugs being addressed.

VirtuallyFun's IBM PS/2 Build and Known Specs

The IBM PS/2 build on which MS-DOS 4.0 is being installed. — (Image credit: @VirtuallyFun on Twitter)

Operating System: MS-DOS 4.0
CPU: Intel i386, a 32-bit single core CPU with a maximum clock rate of 40 MHz
GPU: An XGA-2 (Extended Graphics Array-2) Adapter
RAM: 16 KB
Storage: Gotek Floppy Emulator for USB

It's worth noting that VirtuallyFun, aka Neozeed, has quite a presence on both YouTube and GitHub as a retro hardware enthusiast. This includes a video testing out the rare pre-release Microsoft OS/2 build we mentioned earlier, and tons of small applications or software branches. Considering the development background, we wouldn't be surprised to see Neozeed start playing games like Alien Rampage (1996), the most visceral MS-DOS 4 action exclusive.

Or Neozeed did all of this just to see if it would work, and having satisfied their curiosity with a working MS-DOS 4 install on their very own IBM PS/2, they don't need anything else. Though considering MS-DOS 4's notorious RAM demands of up to 92 KB, maximum gaming performance is likely best with a "downgraded" operating system. Somehow, that paradigm still rings true today.

Christopher Harper has been a successful freelance tech writer specializing in PC hardware and gaming since 2015, and ghostwrote for various B2B clients in High School before that. Outside of work, Christopher is best known to friends and rivals as an active competitive player in various eSports (particularly fighting games and arena shooters) and a purveyor of music ranging from Jimi Hendrix to Killer Mike to the Sonic Adventure 2 soundtrack.