There are three major components of WSL that allows Windows 10 to provide a bash shell.
1. Ubuntu / Linux Binary
Genuine unmodified Ubuntu user-mode binaries provided by Canonical and/or downloaded and installed manually or via apt-get
2. Window Subsystem for Linux (WSL)
WSL provides several important components and/or services that enable unmodified Linux binaries to run directly on Windows:
- Linux PicoProcesses: lightweight processes into which Linux binaries, and their dependencies are loaded, bound, and then executed
- Syscalls: Windows kernel infrastructure that exposes a set of syscalls that are compatible with the Linux kernel Application Binary Interface (ABI). The WSL kernel infrastructure was developed by Microsoft and contains no Linux code.
- User-mode tools: Tools including bash.exe and lxrun.exe which are used to launch, and install/uninstall/configure the Ubuntu instance.