Chapter 1: Introduction What is an Operating System? Batch Systems Time Sharing Systems Personal Computer Systems Parallel or Multiprocessor Systems Distributed Systems Real -Time Systems Handheld Systems
What is an Operating System? A program that acts as an intermediary between a user of a computer and the computer hardware (manages a computer’s hardware). Operating system is an interface between user and hardware, between application program and hardware and between two programs. Operating system goals: Provide an environment in which a user can execute programs. Execute user programs and make solving user problems easier. Make the computer system convenient to use. Use the computer hardware in an efficient manner.
Computer System Components Computer system can be divided into four components: Hardware – provides basic computing resources CPU, memory, I/O devices Operating system Controls and coordinates use of hardware among various applications and users Application programs – define the ways in which the system resources are used to solve the computing problems of the users Word processors, compilers, web browsers, database systems, video games Users People, machines, other computers The components of a computer system are its hardware, software and data.
Abstract View of System Components
Operating System Definitions OS is a resource allocator Manages and allocates all resources (CPU time, memory space, file-storage space, I/O devices, etc.) Decides between conflicting requests for efficient and fair resource use OS is a control program Controls execution of programs to prevent errors and improper use of the computer (control operations of I/O devices) Parts of the OS “ The one program running at all times on the computer” is the kernel . Shell – it is an interface between user and the kermel. An application program is started from shell. Everything else is either a system program (ships with the operating system) , or an application program.
Layers of the Operating System hardware Text editor Command-line interpreter (shell) VI sh pico a.out open( ), read( ), close( ) write( ) fork( ) kernel who cc Application programs Compilers System calls
A more detailed (layer) structure of OS User programs Shells, compilers, interpreters, libraries System-call interface to kernel Signals terminal handling character I/O system terminal drivers File system Swapping block I/O system Disk drivers CPU scheduling Page replacement Virtual memory Kernel interface to the hardware Terminal controllers terminals Device controllers disks Memory controllers Physical memory kernel
Kernel Services I/O Management Process Management Memory Management File Systems Management Device Drivers Management System Calls (Application Program Interface) Interprocess Communication Protection System Networking
Computer Startup Small piece of code –
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