uses a client/server architecture

Apps invoke services via local procedure calls

uses a microkernel model

Figure 7.10. Windows NT

Each process is isolated in a 32bit Virtual Machine

API calls are intercepted by subsystems stubs in the upper 2 GB

Each VM works as a Win32 computer

VMs can work as other OSs machine: DOS, OS2, Win 3.1 etc.

VM machines communicate with the NT executive or other VMs by a message-passing procedure call similar to RPCs.