<P> Operating system development is one of the most complicated activities in which a computing hobbyist may engage . A hobby operating system may be classified as one whose code has not been directly derived from an existing operating system, and has few users and active developers . </P> <P> In some cases, hobby development is in support of a "homebrew" computing device, for example, a simple single - board computer powered by a 6502 microprocessor . Or, development may be for an architecture already in widespread use . Operating system development may come from entirely new concepts, or may commence by modeling an existing operating system . In either case, the hobbyist is his / her own developer, or may interact with a small and sometimes unstructured group of individuals who have like interests . </P> <P> Examples of a hobby operating system include Syllable . </P> <P> Application software is generally written for use on a specific operating system, and sometimes even for specific hardware . When porting the application to run on another OS, the functionality required by that application may be implemented differently by that OS (the names of functions, meaning of arguments, etc .) requiring the application to be adapted, changed, or otherwise maintained . </P>

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