What is L4

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L4 started as a kernel developed by Jochen Liedtke, designed from the ground up with performance as a primary goal. The kernel was purely written in x86 assembler and highly optimized.

Over the time several groups have adapted the L4 idea and developed other kernels. Among performance, new goals were maintainability and portability. Nowadays the kernels are written in higher-level languages like C++ and are running on many different architectures.

Due to the diversity of existing kernels, the term L4 now denotes a microkernel family rather than a single kernel.

All L4 kernels have a common spirit:

  • Only put the absolutely necessary functionality in the kernel, all other functionality shall be implemented on top of the kernel in user applications
  • No policy in the kernel, the kernel shall only implement mechanisms.