POSIX is the IEEE's Portable Operating System Interface for Computer Environments. The standard provides compliances criteria for operating system services and is designed to allow programmers to write applications that can easily port across operating system. Part of the features of POSIX is its support for real-time applications such as mutex, semaphore, real-time scheduling, priorities etc. For this practical we use a version that is ported for the Windows environment, called pthread. You can also have a look at for more explanation on how pthread works.