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  • 1 Overview
    운영체제 2021. 4. 7. 02:29

    Overview

    - Operating System acts an intermidiary between the user of a computer and the computer hardware.
    - Operating System is to provide an environment in which a user can execute programs in a convenient and effcient manner.
    - Operating System is software that manages the computer hardware.
    - Operating System is large and complex. piece by piece approach is needed and each pieces should be well-delineated portion of the system with carefully defined inputs, outputs, and functions.

    OBJECTIVES

    - Describe the general organization of a computer system and the role of interrupts.
    - Describe the components in a modern multiprocessor computer system.
    - Illustrate the transition from user mode to kernel mode.
    - Discuss how operating systems are used in various computing environments.

    1.1 What Operating Systems Do

    - A computer system can be devided roughly into four components : the hardware, the operating system, the application programs, and a user.

    1.1.1 User View

    - To a user, the operating system provide ease of use. A user don't need to pay attention to resource utilization - how various hardware and software resources are shared.

    1.1.2 System View

    - To the computer, the operating system is the program most intimately involved with the hardware. The operating system is kinda resource allocator. - CPU time, memory space, storage space, I/O devices, etc. these resources should be controlled.
    - To the computer, the operating system is kinda control program. A control program manages the execution of user programs to prevent erros and improper use of the computer. It is especially concerned with the operation and control of I/O device.

    1.1.3 Defining Operating Systems

    - In general, we have no completely adequate definition of an operating system. Operating systems exist becuase they offer a reasonable way to solve the problem of creating a usable computing system. Since bare hardware alone is not particularly easy to use, application program are developed. These programs require certain common operations, such as those controlling the I/O devices. The common functions of controlling and allocating resources are then brought together into on piece of software: the operating system.
    - The operating system is the one program running at all times on the computer. called the kernel.

    1.2 Computer-System Organization

    - In computer system, There are common bus connects device controllers. bus provides access between components and shared memoery. Each device controller is in charge of a specific type of device. eg, a disk drive, audio device, or graphics display.
    - Operating systems have a devie driver for each device controller. This device driver understands the device controller and provides the rest of the operating system with a uniform interface to the device.
    - The CPU and the device controllers can execute in parallel, competing for memory cycles. To ensure orderly access to the shared memory, a memory controller synchronizes access to the memory.

    1.2.1 Interrupts
    1.2.1.1 Overview

    -Hardware trigger an interrupt at any time by sending a signal to the CPU, usually by way of the system bus.
    -Interrupts are use for many other purposes as well and are a key part of how operating systems and hardware interact.
    -When the CPU is interrupted, it stops what it is doing and immediately transfers execution to a fixed location. fixed location usually contains the starting address where the service routine for the interrupt is located.
    -The interrupt service routine executes; on completion, the CPU resumes the interrupted computation. The interrupt architecture must also save the state information of whatever was interrupted, so that it can restore this information after servicing the interrupt.
    Interrupt vector is array of addresses indexed by a unique number, given with the interrupt request, to provide the adrress of the interrupt service routine for the interrupting device.

    1.2.1.2 Implemntation

    -The CPU hardware has a wire called the interrupt-request line that the CPU senses after executing every instruction. When the CPU detects signal on the interrupt-request line, it reads the interrupt number and jumps to the interrupt-handler routine (=interrupt-service routine)  by using that interrupt number as an index into the interrupt vector.

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