The lowest layer into which a large operating system is sub divided, each layer dealing with some aspect of the system hardware. The kernel is responsible for allocating hardware resources to the processes that make up the operating system and to the programs running under the operating system. Formal verification of the kernel is usually necessary for systems professing high integrity or security. See security kernel.
Nucleus is a near-synonym for kernel and tends to be used where the effects are achieved by a mixture of normal programming and microcoding. The microprogram is written in such a way as to complement the functions achieved by the normal code, with a gain in running speed.