Microsoft has made a significant announcement after 10 years since the release of the MS-DOS 1.25 and 2.0 code. They have opened the initial texts of the operating system MS-DOS 4.0, which was originally released in 1988 and developed in collaboration with IBM. The code is now open under the MIT license, allowing users to freely modify and use it in their products. The product is written in assembler for processors 8086. Emulators like pcel and 86Box can be used to launch it.
The release of MS-DOS 4.0 is notable for introducing a graphic interface and mouse support, as well as support for disks larger than 32 MB (up to 2 GB). It also added a file manager called Dosshell, support for Expanded Memory Specification (EMS), and features such as Fastopen and Fastseek.