What Is Operating System :
A program that acts as an intermediary between a user of a computer and the computer hardware.
Goals of Operating Systems :
l1. Execute user programs and make solving user problems easier.
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Objectives of Operating Systems :
1. To provide a grand tour of the major operating systems components
2. nTo provide coverage of basic computer system organization
Operating System Structure :
nMultiprogramming needed for efficiency
lSingle user cannot keep CPU and I/O devices busy at all times
lMultiprogramming organizes jobs (code and data) so CPU always has one to execute
lA subset of total jobs in system is kept in memory
lOne job selected and run via job scheduling
lWhen it has to wait (for I/O for example), OS switches to another job
nTime sharing (multitasking) is logical extension in which CPU switches jobs so frequently that users can interact with each job while it is running, creating interactive computing
lResponse time should be < 1 second
lEach user has at least one program executing in memory [process
lIf several jobs ready to run at the same time [ CPU scheduling
lIf processes don’t fit in memory, swapping moves them in and out to run
lVirtual memory allows execution of processes not completely in memory
