Not everyone who lives after the year 2000 knows or even heard about Microsoft Disk Operating System, or better known as MS-DOS.
When Microsoft was founded by Bill Gates and Paul Allen on April 4, 1975, to develop and sell BASIC interpreters for the Altair 8800, it was the MS-DOS that rose the company to dominate the PC operating system market in the mid-1980s. Since then, MS-DOS was the main operating system for IBM PC compatible PCs until the 1990s.
This was until the operating systems experienced a major shift from command line towards graphical user interface (GUI), starting with Windows ME (Millennium Edition) which began ditching the real MS-DOS support.
MS-DOS was first launched on August 12, 1981. Fast forward to September 28, 2018, Microsoft is re-open-sourcing MS-DOS to GitHub. This is after in 2014 that Microsoft released the MS-DOS source code (versions 1.25 and 2.0) via the Computer History Museum.
According to Microsoft's Senior Program Manager Richard Turner who announced the news, the reason is because "it's much easier to find, read, and refer to MS-DOS source files if they're in a GitHub repo than in the original downloadable compressed archive file."
Microsoft has released two different versions of DOS as open source. They are DOS 1.25 and DOS 2.0.
DOS 1.25 was used as the basis for all of the non-IBM versions of DOS, while in MS-DOS version 2.0, Microsoft introduced a number of significant features such as IBM XT hard drive support (up to 32MB formatted), user-installable device drivers, non-multi-tasking child processes, and ANSI.SYS.
DOS 2.0 was also the first version to support 5.25-inch disks in capacities of 180KB and 360KB.
According to Richard Turner:
- All the source for MS-DOS 1.25 and 2.0 was written in 8086 assembly code.
- The source code for the initial release of 86-DOS dates from around December 29th 1980.
- The MS-DOS 1.25 code dates from around May 9th 1983, and is comprised of just 7 source files, including the original MS-DOS Command-Line shell – COMMAND.ASM.
- MS-DOS 2.0 dates from around August 3rd 1983, and grew considerably in sophistication (and team size), and is comprised of 100 .ASM files.
- There are some documentation files interspersed with the source and object files.
Microsoft’s decision to open source MS-DOS like this might not seem that important, considering that the operating system is regarded as an ancient legacy of the computer history.
While there are alternatives to MS-DOS in the market, such as FreeDOS and DOSBox, the MS-DOS is a critical component of the history of the PC, and its development mirrors the deployment of features and technology in much of the market through the 1980s.
By having MS-DOS on GitHub, developers can easily take a peek into what was Microsoft's secret sauce back in the 1980s, understanding how the operating system was that made Microsoft the company almost synonymous to computers.
However, Microsoft intends to keep the source files static.
What this means, the files are only for reference and internal experimentation only. Microsoft asks that users refrain from Pull Requests that suggest source file modification.