Transcript Computer Science 101

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