Comparison of operating systems

Because of the large number and variety of available Linux distributions, they are all grouped under a single entry; see comparison of Linux distributions for a detailed comparison. There is also a variety of BSD and DOS operating systems, covered in comparison of BSD operating systems and comparison of DOS operating systems.

Nomenclature

The nomenclature for operating systems varies among providers and sometimes within providers. For purposes of this article the terms used are;

kernel

In some operating systems, the OS is split into a low level region called the kernel and higher level code that relies on the kernel. Typically the kernel implements processes but its code does not run as part of a process.

hybrid kernel

monolithic kernel

Nucleus

In some operating systems there is OS code permanently present in a contiguous region of memory addressable by unprivileged code; in IBM systems this is typically referred to as the nucleus. The nucleus typically contains both code that requires special privileges and code that can run in an unprivileged state. Typically some code in the nucleus runs in the context of a dispatching unit, e.g., address space, process, task, thread, while other code runs independent of any dispatching unit. In contemporary operating systems unprivileged applications cannot alter the nucleus.

License and pricing policies vary widely among different systems. Among others, the tables below use the following terms:

BSD

BSD licenses are a family of permissive free software licenses, imposing minimal restrictions on the use and distribution of covered software.

bundled

The fee is included in the price of the hardware