Page "Mach (kernel)" Paragraph 12

Mach developed on Accent's IPC concepts, but made the system much more UNIX-like in nature, even able to run UNIX programs with little or no modification.

To do this, Mach introduced the concept of a port, representing each endpoint of a two-way IPC.

Ports had security and rights like files under UNIX, allowing a very UNIX-like model of protection to be applied to them.

Additionally, Mach allowed any program to handle privileges that would normally be given to the operating system only, in order to allow user space programs to handle things like interacting with hardware.