The message-passing facility in Win

The message-passing facility in Windows is called the advanced local procedure call (ALPC) facility.
It is used for communication between two processes on the same machine.
It is similar to the standard remote procedure call (RPC) mechanism that is widely used, but it is optimized for and specific to Windows. (Remote procedure calls are covered in detail in Section 3.6.2.)
Like Mach, Windows uses a port object to establish and maintain a connection between two processes. Windows uses two types of ports: connection ports and communication ports.