What programming language was Windows 10 written in?

Windows 10, released by Microsoft in 2015, is the latest model and the last operating system in the continuation of the Windows series since 1985. What programming language was used to develop this operating system, which is still being developed 4 years after its release?

According to Microsoft engineer Axel Rietschin, Windows 10 shares the initial code with Windows 8, 7, Vista, and XP, and is developed based on the same underlying code as the previous Windows series.

The Windows series has undergone significant refactoring from generation to generation, adding important new features to increase performance and security, while maintaining compatibility with advanced versions. In other words, Windows 10 is the latest operating system, but the basic code is inheriting the old ones.

He asserts that most of the core kernel of the operating system is written in the C language, the progenitor of the C language. The Windows Research Kernel leaked and published on GitHub is outdated and incomplete, but it provides important insights into the question of what language Windows 10 was written in.

Most of the file system and networking system operating in kernel mode are written in C language, and some are written in C++. It is said that C++ is increasing from C language as it approaches user mode and is recently developed. In fact, it is difficult to analyze which programming language was used to make the entire Windows 10, but it is estimated that 98% of the cases will be C or C++.

He says that while developing Windows 10 and the Windows series is a great project, many people don’t realize that Windows is a huge operating system. All the source codes that make up the Windows source code, including the test code, are over 500 GB and the number of files is over 4 million. Even if the source tool development code that composes the operating system workstation and server product flows all the time, it will take a year, so if you decide to decrypt it, you may not have enough time for the rest of your life.

In a Windows project, a significant amount of code is generated by many programmers every day. Therefore, it is said that it will be impossible for one person to see all the code added to the Windows project in one day. Related information can be found here.