Operating System PDF
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Nile University of Nigeria
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This document is about operating systems. It provides an overview of operating systems, including their history, components, and functions. It also covers the execution of programs and security topics.
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OPERATING SYSTEM Operating system OS is the software that controls the overall operation of a computer. Store and retrieve files Schedule programs for execution Coordinate the execution of programs Example of OS Windows, UNIX, LINUX, Mac OS HISTORY OF COMPUTING The computer...
OPERATING SYSTEM Operating system OS is the software that controls the overall operation of a computer. Store and retrieve files Schedule programs for execution Coordinate the execution of programs Example of OS Windows, UNIX, LINUX, Mac OS HISTORY OF COMPUTING The computers of the 1940s and 1950s were not very flexible or efficient. Machines were large Program execution required quite number of preparation of equipment Mounting magnetic tapes Placing cards in card readers Setting switches, etc. Each execution of a program is called job. User needed to wait for one to finish his program execution. Computer operator Collect program requirement Load in mass storage OS read and execute the program one at a time Batch processing systems (1950s – 1960s’), the jobs residing in mass storage wait for execution in a job queue. Jobs are executed in first in, first out (FIFO). The instruction is encoded by a job control language JCL, and store with the job in the job queue. When job is selected for execution the OS printed instruction where they could be read and followed by the computer operator Drawback to using a computer operator. Things need to be changed as they occur. Computer games. To accommodate these needs, new OS were developed that allowed a program execution, by user through remote terminals (workstation) with a feature called interactive processing. Terminal is consisted of little more than an electronic typewriter with which the user could type input and read the computer's response that was printed on paper. Problem with job processing before real-time processing executing program would be frustrating if the machine did not respond on time. Problem of real-time processing on interactive system, multiple users might required to do something at same time and real-time considerations presented obstacles. If the OS insisted on executing one at a time. TYPES OF SOFTWARE Application software: Perform user tasks System software: Provides an infrastructure that the application software is requires, similar to nation’s infrastructure. Utility: It is used to support the computer infrastructure in contrast to application software, which is aimed at directly performing tasks that benefit ordinary users. utility software is not considered part of the operating system, and users often install replacements or additional utilities. Data compression Anti-virus, etc. COMPONENTS OF OS Shell portion of OS handles the communication between the user and the OS by means of graphical-user interface (GUI). KERNEL AND ITS COMPONENTS An operating system's kernel contains those software components that perform the very basic functions required by the computer installation. File manager, whose job is to coordinate the use of the machine's mass storage facilities. More precisely record of each file in mass storage (location, which user have access to a file, portion of mass storage available for storing new file). Collection of device drivers, whose job is to communicate with controllers to carry out operation on peripheral devices attached to machine (such as printer, monitor). Memory manager, whose job is to allocate space in main memory for a program and keep track on when main memory space is occupied or not. Virtual memory is the portion of mass storage that is allocated to store a content that is meant to store in main memory, transfer between the two being made when required. Boot loader: Program in ROM Run by the CPU when power is turned on Transfers operating system from mass storage to main memory Executes the operating system PROGRAM EXECUTION A program is a static set of instructions A process (task or job) is the activity of executing a program A process may occupy more memory space than a program The process state is the current status of the activity. When a user select a program to run in a computer, the program becomes a process and it will go through the following execution states Initialization Ready Running Waiting/Interrupted Halted CPU SCHEDULING ALGORITHM First come first serve FCFS Shortest job first SJF Shortest job first with preemption PROCESS ADMINISTRATION Scheduler and dispatcher The scheduler maintains a process table within the OS; When a user runs a program, it creates a new entry in the process table. After the initialization, the scheduler will add it to the ready pool of processes. If a process cannot continue execution for some reasons (e.g. waiting for data), it will be added to the waiting pool. If a process is finished, the scheduler will remove it from the process table. Dispatcher controls the allocation of time to these activities. SECURITY Attacks from outside Login credentials Problems Insecure passwords Counter measures Auditing software Attacks from within Problem: Unruly processes Counter measures: Control process activities via privileged modes and privileged instructions