Open source MS-DOS 4.0
Microsoft just wrote on how they are Open sourcing MS-DOS 4.0:
Today, in partnership with IBM and in the spirit of open innovation, we’re releasing the source code to MS-DOS 4.00 under the MIT license.
MS-DOS was the de-facto PC operating system, until Windows 95 hid it deep into the GUI. It evolved from a clone of CP/M, the operating system from Digital Research that was popular on Z80 machines. To be fair it was technically limited, with a maximum on 640KiB of RAM usable, a file system that didn’t support filenames longer than 8 ASCII characters + 3 for the extension, and a command line interface. A mediocre product at best, that sold well as IBM chose it for their IBM PC.
This version, MS-DOS 4.00, is a bit special. Released in 1986, it was compatible with MS-DOS 3 and included a preemptive multitasking feature to allow running a program in the background, while still not addressing the memory limitation. Subsequent versions of MS-DOS dropped the feature.
The most common DOS 4 version was named PC-DOS, came from IBM instead, and didn’t include the multitasking ; it was a different product albeit also compatible with MS-DOS 3.
For historical purpose, this is great news.