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Lecture Operating system concepts - Lecture 17

The various processes in an operating system must be protected from one another’s activities. For that purpose, various mechanisms exist that can be used to ensure that the files, memory segments, CPU, and other resources can be operated on by only those processes that have gained proper authorization from the operating system. In this chapter, we examine the problem of protection in great detail and develop a unifying model for implementing protection. | CSC 322 Operating Systems Concepts Lecture - 19: by Ahmed Mumtaz Mustehsan Special Thanks To: Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. (Chapter-3) Silberschatz, Galvin and Gagne 2002, Operating System Concepts, Ahmed Mumtaz Mustehsan, CIIT, Islamabad 1 Chapter 4 File System Lecture-19 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 2 Computers can store information on various storage media The operating system abstracts from the physical properties of its storage devices to define a logical storage unit called a file Files are mapped by the operating system onto non volatile physical devices A file is a named collection of related information that is recorded on secondary storage File Systems Introduction Lecture-19 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 3 For a user’s perspective, a file is the smallest allotment of logical secondary storage (i.e., data supposedly cannot be written to secondary storage unless written in a file) Files commonly represent . | CSC 322 Operating Systems Concepts Lecture - 19: by Ahmed Mumtaz Mustehsan Special Thanks To: Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. (Chapter-3) Silberschatz, Galvin and Gagne 2002, Operating System Concepts, Ahmed Mumtaz Mustehsan, CIIT, Islamabad 1 Chapter 4 File System Lecture-19 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 2 Computers can store information on various storage media The operating system abstracts from the physical properties of its storage devices to define a logical storage unit called a file Files are mapped by the operating system onto non volatile physical devices A file is a named collection of related information that is recorded on secondary storage File Systems Introduction Lecture-19 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 3 For a user’s perspective, a file is the smallest allotment of logical secondary storage (i.e., data supposedly cannot be written to secondary storage unless written in a file) Files commonly represent programs (both source and object code) and data Data file contents may be numeric, alphabetic, alphanumeric, or binary Files may be free form (e.g., text files) or rigidly formatted In general, a file is a sequence of bits, bytes, lines, or records, whose meaning is defined by the file’s creator and user File Systems Introduction Lecture-19 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 4 Many important applications need to store more information then have in virtual address space of a process Must store large amounts of data Gigabytes -> terabytes -> petabytes The information must survive the termination of the process using it. Lifetime can be seconds to years Must have some way of finding it! Multiple processes must be able to access the information concurrently. File Systems Lecture-19 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 5 Disks are used to store files Information is stored in blocks on the disks Can read and write blocks File Systems Lecture-19 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 6 Use