Windows NT Native API

One of the authors of the well-known book "Windows Internals" talks about Windows NT native APIs and other related topics such as Win32 DLLs, kernel/user mode, etc.

The Native API is equivalent to the system call interface on traditional monolithic operating systems such as most UNIXes. On most UNIXes, however, the system call interface is well documented and is generally available for use by standard applications.

There is a nice picture showing the architecture of Windows NT DLLs and system services.