 What is an operating system? What is an operating system?  Where does the OS fit in? Where does the OS fit in?  Services provided by an OS Services provided by an OS  Why are Operating Systems Important? Why are Operating Systems Important?  Hierarchical view of computer system Hierarchical view of computer system  Layers of a Computer System Layers of a Computer System  Operating System Components Operating System Components  Operating System Overview Operating System Overview  Protection Protection

 An interface between users and hardware  Allows convenient usage; hides the tedious stuff  Allows efficient usage; parallel activity, avoids wasted cycles  Provides information protection Go back

 Facilities for program creation  editors, compilers, linkers, debuggers, etc.  Program execution  loading in memory, I/O and file initialization.  Access to I/O and files  deals with the specifics of I/O and file formats.  System access  resolves conflicts for resource contention.  protection in access to resources and data. Go back

End User Programmer Operating- System Designer Computer Hardware Operating-System Utilities Application Programs Go back

The CPU is wasted if a job waits for I/O. This leads to: ◦ Multiprogramming ( dynamic switching ). While one job waits for a resource, the CPU can find another job to run. It means that several jobs are ready to run and only need the CPU in order to continue. All of this leads to: ◦ memory management ◦ resource scheduling ◦ deadlock protection OPERATING SYSTEM COMPONENTS Go back

Other Characteristics include:  Time Sharing -Multiple jobs are executed by switching the CPU between them. In this, the CPU time is shared by different processes, so it is called as “Time sharing Systems”.  Multiprocessing - Tightly coupled systems that communicate via shared memory. Used for scientific applications. Used for speed improvement by putting together a number of off-the-shelf processors.  Distributed Systems - Loosely coupled systems that communicate via message passing. Advantages include resource sharing, speed up, reliability, communication.  Real Time Systems - Rapid response time is main characteristic. Used in control of applications where rapid response to a stimulus is essential. OPERATING SYSTEM OVERVIEW Characteristics Go back

CPU A clock prevents programs from using all the CPU time. This clock causes an interrupt that causes the operating system to gain control from a user program. Protection For machines connected together, this protection must extend across: Shared resources, Multiprocessor Architectures, Clustered Systems The practice of this is called “distributed operating systems”. Go back