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Computer Science 101 The Virtual Machine: Operating Systems From Hardware to Software • Naked machine – Hardware bereft of any helpful user-oriented features – Data as well as instructions must be represented in binary • To make a Von Neumann computer usable: – Create an interface or virtual machine between the user and the hardware From Hardware to Software • The virtual machine – System software: collection of computer programs that manage the resources of a computer and facilitate access to those resources – Software: sequences of instructions that solve a problem Types of System Software Types of System Software • Operating system – Communicates with users – Determines what they want – Activates other system programs, applications packages, or user programs to carry out their request Some Typical OS Commands Terminal-based user interface (prompt and keyboard input of commands) OS Responsibilities • Major responsibilities of operating systems – User interface management (a receptionist) – Control of access to system and files (a security guard) – Program scheduling and activation (a dispatcher) – Efficient resource allocation (an efficiency expert) – Deadlock detection and error detection (a traffic officer) History of Operating Systems • First-generation system software – Roughly 1945–1955 – No operating systems and very little software support • Second-generation system software – Called batch operating systems (1955–1965) • Command language – Commands specifying to the operating system what operations to perform on programs Batch Processing Time Sharing Operating Systems • Third-generation operating systems – Multiprogrammed operating systems (1965– 1985) – Many programs can be stored in memory – Allows programmer to enter system commands, programs, and data online – Allows multiple programmers to run programs simultaneously on one computer (time sharing) A Time-Sharing System Network Operating System • Much of the computing was done remotely in the office, laboratory, classroom, and factory • Fourth-generation operating system (1985– present) The Future • Multimedia user interfaces – Will interact with users and solicit requests in a variety of ways • Parallel processing operating system – Can efficiently manage computer systems containing tens, hundreds, or even thousands of processors • Distributed computing environment – Users do not need to know the location of a given resource within the network