What an Operating System is Not

An operating system is not:

• the hardware, which provides the fundamental resources managed by the operating system. On the other hand, in some hardwares some OS-defined abstractions such as processes are built in.
• a programming language, though a programming language is needed to write an operating system. Both programming languages and operating systems beautify the hardware by providing higher-level abstractions. The difference is that a programming language provides abstractions like records and arrays that are temporary and private to a process while an operating system provides those that are persistent and shareable by multiple processes Sometimes an operating system is integrated with a programming language.
• a database system, which is typically built on top of an operating system. Both database and operating systems provide abstractions shared by multiple processes. The database abstractions are built on top of operating systems because and are typically much more complex and less efficient. As computers become faster, it makes sense to integrate operating and database systems.
• network software, thought both OS and network software address communication between distributed computers. The difference is that network software address inter-computer communication while an OS provides inter-process communication. Inter-process communication is typically built on top of inter-computer communication, though in some systems, as we will see later, the two are integrated for efficiency reasons.

• a set of utility programs such as editors, mailers, compilers and loaders, which use the facilities provided by an operating system.