File Systems - Advanced Operating System - Lecture Slides, Slides of Computer Science

These are the lecture Slides of Advanced Operating System which includes Virtual Memory Performance, Resident Set Management, Allocating Pages, Page Fault Frequency Algorithm, Working Set Strategy, Thrashing, Replacement Policy, Multiprogramming Level etc. Key important points are: File Systems, Goals of File System, Types of Files, Logical File Structure, Implementation Requirements, Contiguous Allocation, Linked Allocation, Indexed Allocation, Unix File System

Typology: Slides

2012/2013

Uploaded on 03/20/2013

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File Systems
COMP755 Advanced Operating
Systems 1
File Systems
COMP755 Advanced Operating
Systems
OS Purpose
An operating system maps a logical
concept onto the physical hardware.
The OS makes disk drives (of various
makes and models) with cylinders, heads
and sectors look like files with names,
security and data streams.
Goals of a File System
Easily identify files
Provide secure access
Allow sharing of data
Allocate disk space
Provide rapid access
Protection against loss of data
Be hardware transparent
Types of Files
To the OS, bits are bits, the file type
doesn’t matter.
The OS provides low level functionality
upon which higher level file structures can
be built.
Basic OS I/O functions are:
read a block, write a block, open, close and
delete
Logical File Structure
Most modern systems use a directory tree
structure
A file can be uniquely specified by it’s
position in the tree,
/here/there/file.type
Both files and directories have access
rights.
To the OS, directories are just files
containing the names of other files.
Disk space is allocated in units, often
called clusters.
I/O must be done on a sector or cluster
basis.
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COMP755 Advanced Operating

File Systems

COMP755 Advanced Operating Systems

OS Purpose

  • An operating system maps a logical concept onto the physical hardware.
  • The OS makes disk drives (of various makes and models) with cylinders, heads and sectors look like files with names, security and data streams.

Goals of a File System

  • Easily identify files
  • Provide secure access
  • Allow sharing of data
  • Allocate disk space
  • Provide rapid access
  • Protection against loss of data
  • Be hardware transparent

Types of Files

  • To the OS, bits are bits, the file type doesn’t matter.
  • The OS provides low level functionality upon which higher level file structures can be built.
  • Basic OS I/O functions are:
    • read a block, write a block, open, close and delete

Logical File Structure

  • Most modern systems use a directory tree structure
  • A file can be uniquely specified by it’s position in the tree, /here/there/file.type
  • Both files and directories have access rights. - To the OS, directories are just files containing the names of other files. - Disk space is allocated in units, often called clusters. - I/O must be done on a sector or cluster basis.

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COMP755 Advanced Operating

Implementation Requirements

  • Locate the data on the disk
  • Allocate free space
  • Maintain information about the files (access rights, creation dates, backup flags, etc.)

Contiguous Allocation

  • Use First fit, Best fit, Next fit, etc.
  • Older OS required the administrator to position data on the disk.
  • Difficult to expand
  • Efficient for reading and writing large data sets.
  • Allows for efficient placement to minimize head movement.

Linked Allocation

  • A file consists of a linked list of blocks.
  • Easy expansion of files.
  • Simple to allocate free space.
  • Effective for sequential access, but not too good for random access.
  • Fragile linked system can be corrupted.
  • Used by FAT systems of DOS and Windows

Indexed Allocation

  • An index block contains a table of the blocks containing a file.
  • Files may require multiple index blocks
  • Large files may use multi-level indexing
  • Used by Unix and NTFS

Unix File System

  • Unix has a tree structured directory system.
  • Directories are just files that contain a list of filenames and other directories that are logically contained in the directory.

inodes

  • Information about a file or directory is kept in an inode.
  • Information in an inode includes:
    • access rights
    • owner
    • file size
    • time stamps
    • use count
    • location of the file on the disk

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