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1. n. A minimalist operating system.

2. n. The core of a microkernel architecture operating system like Mach.

3. n. An essential part of any real-time operating system, the kernel consists of the scheduler and context switch routine.

kernel mode

n. A privileged CPU mode. Sometimes called supervisor mode. Parts of the operating system, such as the scheduler, device drivers, and the memory manager, usually execute in kernel mode, whereas application code executes in user mode. The transition from user mode to kernel mode is typically made somewhere inside an OS system call when a software interrupt instruction is executed.

Many of the statically linked single-memory space RTOSes used in embedded systems never place the processor into user mode. Thus, the tasls running on top of such an RTOS can execute any CPU instruction, even those, such as disable interrupts, that could bring the RTOS to its knees.

Note that some processors support multiple levels of privilege, in what are then typically called protection rings.

Contrast with user mode.


(kay bee) pre. The prefix meaning 210. Abbreviated Ki.

  • 1 kibibit: 1 Kibit = 1,024 bits
  • 1 kibibyte: 1 KiB = 1,024 bytes

Note the arcane use of the lower case "k" in the name "kibi," but the use of capital "K" in the abbreviations.

See also binary prefixes, kilo-.