The information stored in the system (both data and code), as well as the physical resources of the computer system, need to be protected from unauthorized access, malicious destruction or alteration, and accidental introduction of inconsistency. In this chapter, we examine the ways in which information may be misused or intentionally made inconsistent. We then present mechanisms to guard against this occurrence. | CSC 322 Operating Systems Concepts Lecture - 20: by Ahmed Mumtaz Mustehsan Special Thanks To: Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. (Chapter-4) Silberschatz, Galvin and Gagne 2002, Operating System Concepts, Ahmed Mumtaz Mustehsan, CIIT, Islamabad 1 Chapter 4 File System File System Implementation Lecture-20 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 2 File Implementation Files stored on disks. Disks broken up into one or more partitions, with separate File System on each partition Sector 0 of disk is the Master Boot Record Used to boot the computer End of MBR has partition table. Has starting and ending addresses of each partition. One of the partitions is marked active in the master boot table Lecture-20 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 3 File Implementation Boot computer => BIOS reads/executes MBR MBR finds active partition and reads in first block (boot block) Program in boot block locates the OS for that partition and reads it in All . | CSC 322 Operating Systems Concepts Lecture - 20: by Ahmed Mumtaz Mustehsan Special Thanks To: Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. (Chapter-4) Silberschatz, Galvin and Gagne 2002, Operating System Concepts, Ahmed Mumtaz Mustehsan, CIIT, Islamabad 1 Chapter 4 File System File System Implementation Lecture-20 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 2 File Implementation Files stored on disks. Disks broken up into one or more partitions, with separate File System on each partition Sector 0 of disk is the Master Boot Record Used to boot the computer End of MBR has partition table. Has starting and ending addresses of each partition. One of the partitions is marked active in the master boot table Lecture-20 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 3 File Implementation Boot computer => BIOS reads/executes MBR MBR finds active partition and reads in first block (boot block) Program in boot block locates the OS for that partition and reads it in All partitions start with a boot block Lecture-20 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 4 A Possible File System Layout Lecture-20 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 5 File System Layout Superblock contains info about the File (. type of File System, number of blocks, ) i-nodes contain info about files Lecture-20 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 6 Allocating Blocks to files Most important implementation issue Methods Contiguous allocation Linked list allocation Linked list using table i-nodes Lecture-20 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 7 (a) Contiguous allocation of disk space for 7 files. (b) The state of the disk after files D and F have been removed. Contiguous Allocation Lecture-20 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 8 Contiguous Allocation Each file occupies a set of contiguous blocks on the disk Pros: Simple – only starting location (block #) and length (number of blocks) are required Random access Cons: Wasteful of space (dynamic -allocation problem) External .
