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The term user space (or userland) refers to all code that runs outside the operating system's kernel. [2] User space usually refers to the various programs and libraries that the operating system uses to interact with the kernel: software that performs input/output , manipulates file system objects, application software , etc.
Microkernel (also abbreviated μK or uK) is the term describing an approach to operating system design by which the functionality of the system is moved out of the traditional "kernel", into a set of "servers" that communicate through a "minimal" kernel, leaving as little as possible in "system space" and as much as possible in "user space".
In most existing systems, switching from user mode to kernel mode has an associated high cost in performance. It has been measured, on the basic request getpid, to cost 1000–1500 cycles on most machines. Of these just around 100 are for the actual switch (70 from user to kernel space, and 40 back), the rest is "kernel overhead".
A kernel is a component of a computer operating system. [1] A comparison of system kernels can provide insight into the design and architectural choices made by the developers of particular operating systems.
Kernel methods owe their name to the use of kernel functions, which enable them to operate in a high-dimensional, implicit feature space without ever computing the coordinates of the data in that space, but rather by simply computing the inner products between the images of all pairs of data in the feature space. This operation is often ...
The AmigaOS Exec kernel was an early example, introduced in 1986 and used in a PC with relative commercial success. The lack of memory protection, considered in other respects a flaw, allowed this kernel to have very high message-passing performance because it did not need to copy data while exchanging messages between user-space programs. [9]
In computer operating systems, a light-weight process (LWP) is a means of achieving multitasking.In the traditional meaning of the term, as used in Unix System V and Solaris, a LWP runs in user space on top of a single kernel thread and shares its address space and system resources with other LWPs within the same process.
This is a compromise between kernel-level ("1:1") and user-level ("N:1") threading. In general, "M:N" threading systems are more complex to implement than either kernel or user threads, because changes to both kernel and user-space code are required [clarification needed]. In the M:N implementation, the threading library is responsible for ...