IPC stands for inter-process communication.
On Unix, inter-process communication can be achieved using pipes. This is inefficient for large amounts of data as the data must be copied. This is generally not a problem as most services are provided by the Unix kernel and Unix is not designed to be extensible.
Microkernel systems, on the other hand, are generally composed of many components. As components are separated by their respective boundaries, unlike the kernel, they cannot arbitrarily examine and modify the caller's state. The advantage is that if the protocol is carefully designed, the callee cannot cause the caller any destructive interference thereby removing the need for the caller to trust the callee thus reducing the former's TCB. When done systematically, this can increase the system's . To this end, microkernels provide richer IPC semantics that include the ability to transfer capabilities and to use mechanisms to copy data.
Continue reading about Mach's IPC system.
- Brian N. Bershad, 1992: The Increasing Irrelevance of IPC Performance for Microkernel-Based Operating Systems (doc, ps, CiteSeerX)