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

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

• 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.