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