L4 microkernel family

L4 is a family of second-generation microkernels, used to implement a variety of types of operating systems (OS), though mostly for Unix-like, Portable Operating System Interface (POSIX) compliant types. L4, like its predecessor microkernel L3, was created by German computer scientist Jochen Liedtke as a response to the poor performance of earlier microkernel-based OSes. Liedtke felt that a system designed from the start for high performance, rather than other goals, could produce a microkernel of practical use. His original implementation in hand-coded Intel i386-specific assembly language code in 1993 sparked intense interest in the computer industry. Since its introduction, L4 has been developed to be cross-platform and to improve security, isolation, and robustness. There have been various re-implementations of the original binary L4 kernel application binary interface (ABI) and its successors, including L4Ka::Pistachio (implemented by Liedtke and his students at Karlsruhe Institute of Technology), L4/MIPS (University of New South Wales (UNSW)), Fiasco (Dresden University of Technology (TU Dresden)). For this reason, the name L4 has been generalized and no longer refers to only Liedtke's original implementation. It now applies to the whole microkernel family including the L4 kernel interface and its different versions. L4 is widely deployed. One variant, OKL4 from Open Kernel Labs, shipped in billions of mobile devices. Specifying the general idea of a microkernel, Liedtke states: A concept is tolerated inside the microkernel only if moving it outside the kernel, i.e., permitting competing implementations, would prevent the implementation of the system's required functionality. In this spirit, the L4 microkernel provides few basic mechanisms: address spaces (abstracting page tables and providing memory protection), threads and scheduling (abstracting execution and providing temporal protection), and inter-process communication (for controlled communication across isolation boundaries).