The operating system is the thing that truly tells the computer how to work in general, and its designers must understand the computer's hardware; applications programs must be designed with specific users in mind, for instance accountants and personnel workers require different programs, and programmers must understand something about accounting or personnel (as the case may be) to serve them.
操作系統是實際指示機器發揮運作功能的部分；應用軟體則是由操作系統上再開發，係依使用者的需要設計，指揮電腦做使用者指定的工作。舉例來說，電腦本身的運作由操作系統軟體指揮，如要它處理會計資料，則需再借重會計的應用軟體。