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Note for Operating Systems - OS by Bhavya Goradia

  • Operating Systems - OS
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  • Mumbai university -
  • Computer Science Engineering
  • B.Tech
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1 Operating Systems - By Bhavya Goradia.

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2 Unit 1 Introduction and Operating Systems Structures Definition: The low-level software that supports a computer's basic functions, such as scheduling tasks and controlling peripherals. Role of Operating Systems: The operating system acts as an interface between the hardware and the programs requesting I/O. It is the most fundamental of all system software programs. Responsibilities of the OS include:  Hiding the complexities of hardware from the user.  Managing between the hardware's resources which include the processors, memory, data storage and I/O devices.  Handling "interrupts" generated by the I/O controllers.  Sharing of I/O between many programs using the CPU. There are two types of software:  System Software - programs that manage the operation of a computer.  Application Software - programs that help the user perform a particular task OS Operations: Following are some of important functions of an operating System.  Memory Management  Processor Management  Device Management  File Management  Security  Control over system performance  Job accounting  Error detecting aids  Coordination between other software and users

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3 Details: Memory Management Memory management refers to management of Primary Memory or Main Memory. Main memory is a large array of words or bytes where each word or byte has its own address. Main memory provides a fast storage that can be accessed directly by the CPU. For a program to be executed, it must in the main memory. An Operating System does the following activities for memory management −  Keeps tracks of primary memory, i.e., what part of it are in use by whom, what part are not in use.  In multiprogramming, the OS decides which process will get memory when and how much.  Allocates the memory when a process requests it to do so.  De-allocates the memory when a process no longer needs it or has been terminated. Processor Management In multiprogramming environment, the OS decides which process gets the processor when and for how much time. This function is called process scheduling. An Operating System does the following activities for processor management −  Keeps tracks of processor and status of process. The program responsible for this task is known as traffic controller.  Allocates the processor (CPU) to a process.  De-allocates processor when a process is no longer required. Device Management An Operating System manages device communication via their respective drivers. It does the following activities for device management −  Keeps tracks of all devices. Program responsible for this task is known as the I/O controller.  Decides which process gets the device when and for how much time.  Allocates the device in the efficient way.  De-allocates devices.

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4 File Management A file system is normally organized into directories for easy navigation and usage. These directories may contain files and other directions. An Operating System does the following activities for file management −  Keeps track of information, location, uses, status etc. The collective facilities are often known as file system.  Decides who gets the resources.  Allocates the resources.  De-allocates the resources. Other Important Activities Following are some of the important activities that an Operating System performs −  Security − By means of password and similar other techniques, it prevents unauthorized access to programs and data.  Control over system performance − Recording delays between request for a service and response from the system.  Job accounting − Keeping track of time and resources used by various jobs and users.  Error detecting aids − Production of dumps, traces, error messages, and other debugging and error detecting aids.  Coordination between other softwares and users − Coordination and assignment of compilers, interpreters, assemblers and other software to the various users of the computer systems. Functions of operating systems: Operating system performs the following functions: Booting: Booting is a process of starting the computer operating system starts the computer to work. It checks the computer and makes it ready to work.

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