Chapter 3: File Systems

1
Chapter 3 File Systems

• A Guide to Operating Systems
• Troubleshooting and Problem Solving

2
Chapter Objectives

• Understand the basic functions of all file
  systems
• Describe the major elements of the DOS and
  Windows 3.1/ 3.11 file system
• Compare and contrast the Windows 95/ 98 file
  system (FAT16 and FAT32) with the older DOS/
  Windows 3.1 file system
• Describe the fundamental features of the UNIX
  file system
• Describe the basics of the Macintosh file system

3
Understanding File System Functions

• Partition and format disks to store and retrieve
  information
• Establish file naming conventions
• Provide utilities for functions such as file
  compression and disk defragmentation
• Provide for file and data integrity
• Provide storage media management functions

4
A File System Metaphor
5
Data Files Contain

• Text
• Images
• Music

• Sounds
• Video
• Web Pages for the Internet

6
Block Allocation

• Keeps track of where specific files are stored on
  disk
• In DOS and Windows, these are clusters
• Hard disk platter has two sides (read/ write head)

• Clusters are mapped to sectors, heads, and tracks
• Divided into logical blocks
• Tracks that line up on platter are called
  cylinders

7
Block Allocation

• Two techniques are used to store data
• A fixed portion of the disk is used (FAT)
• Various locations on the disk are used (UNIX and
  NTFS)

8
Partitions and Related Components

• Divides hard drive into sections
• Creates multiple logical volumes that you assign
  drive letters to
• Partition table (DOS, Mac OS, and Windows

• Disk label in UNIX
• Boot block in UNIX
• Master boot record in Windows (MBR)

9
The DOS/Windows 3.1 File System

• Uses a file allocation table (FAT) file system
• Use of 8.3 file names which can be up to 8
  characters long followed by a period and an
  extension of 3 characters
• With DOS prior 4.0, the maximum size of file
  system was 32 MB (FAT12)
• With MS-DOS from 4.0, the maximum size was 2 GB
  (FAT16)

10
Partitioning

• The FAT file system supports two partitions per
  hard drive - a primary and a secondary partition
• A secondary partition may be divided into a
  maximum of three logical drives

11
Sample DOS Partition Table Structure

• FDISK is used to modify partition information

12
MS-DOS FDISK Utility
13
FDISK Partition Information Screen
14
Formatting Placing a file system on a
partition

• Boot block contains information about disk
  (number of tracks and sectors per track)
• Boot block contains small program to start
  operating system

• In DOS use the format command
• Writes all of the file system structure to disk
• A floppy uses first sector as the boot block

15
FORMAT Command Switches
16
Root Directory and File Attributes

• Root directory contains the following
• name, start cluster, file size, file modification
  date and time
• every partition is a fixed size
• File attributes (characteristics)
• hidden, read only and archive

17
Clusters

• Not fixed in length
• If a file does not exactly match the disk space
  available in the cluster, there will be unused
  space at the end of cluster
• Unused spots in FAT are marked as bad clusters
• The largest possible partition in FAT is 4 GB

18
Hard Disk Cluster Reference
19
Typical FAT Directory Structure

• The FAT table and root directory are found at the
  beginning of each partition, and are always at
  the same location.
• Each item in the directory consists of 32 bytes

20
Extensions

• SYS extension is generally the device driver
• COM or EXE extensions are program files that the
  operating system can execute
• BAT extensions are batch files of commands that
  can be executed as if they were typed on the
  keyboard
• Filename and extension cannot contain spaces

21
ATTRIB Arguments and Switches
22
DOS File System Utilities

• CHKDSK checks the contents of directories and
  verifies the consistency of FAT tables
• /F, for Fix allows you to correct problems

• SCANDISK is a menu driven interface
• Copies files it will manipulate to a disk
• Conducts some of the same tasks as CHKDSK

23
Another DOS Utility

• Defragment - rewrites files to a disk so that
  they are contiguous
• Looks for empty FAT location and uses the cluster
  indicated
• Continues to use the next empty cluster until no
  more free clusters are found

24
More About Defragmentation

• The Disk Defragmenter utility maximizes access
  time and makes it faster to write new files to
  disk
• Floppy disks do not need to be defragmented
• The hard disk should be defragmented on a regular
  basis

25
Windows 95/ 98 File System

• FAT16 is similar to the system used in DOS/ Win
  3.1
• FAT32 is a new system introduced in Windows 95,
  release B
• Both the FAT 16 and FAT32 file system for Windows
  95/ 98 have features in common with the DOS
  version of the FAT16 system with some new ideas

26
Windows 95/ 98 FAT16

• File names may contain as many as 255 characters
• File names are not case sensitive
• File name can include spaces and several
  characters that 8.3 names cannot (./\)

27
DOS 8.3 Filenames versus Long Filenames (LFN)
28
Long Filenames (LFN)

• The LFN is stored by using a series of additional
  directory entries
• It can contain up to 13 characters in upper or
  lower case
• Unicode allows for representation of any
  character in any language

29
Long Filenames (LFN)

• Unicode is a 16-bit code
• ASCII (American Standard Code for Information
  Interchange) uses an entire byte to represent
  each character
• Limits number of characters represented to 255

30
Long Filename Storage Scheme
31
FAT32

• Gets around the problem of cluster size
• Allows the partitions to be up to 8 GB
• Blocks can be allocated with up to 8 KB
• The maximum partition size will be raised to 32
  GB
• Dont use FAT32 if you plan to access your hard
  disk from other operating systems

32
Windows 95/98 File System Utilities

• Windows 95/ 98 includes the capability to create
  compressed disk volumes
• Windows 95 also has a defragmentation utility
  that will run from system scheduler
• No other programs should be running while using
  the defragmentation utility

33
DEFRAG Utility
34
Windows NT File Systems

• Windows NT supports two types of file systems
• The extended FAT16 system
• The New Technology File System (NTFS)
• Both systems are Portable Operating System
  Interface (POSIX) compliant

35
New Technology File System (NTFS) Features

• Built-in security
• Ability to use larger disks and larger files
• Ability to compress file and directory contents
  on the fly
• Better recoverability and stability
• Less disk fragmentation

36
NTFS Numerical Equivalents
37
NTFS Default Cluster Sizes
38
Tracking Files and Clusters

• NTFS tracks files and clusters using a Master
  File Table (MFT)
• The MFT is located at the beginning of the
  partition
• The Boot sector is located ahead of the MFT
• Normally the MFT takes up 1 MB

39
NT Disk Administrator

• NT Disk Administrator allows you to partition and
  format disks
• Allows you to change disk and partition
  attributes
• Performs disk maintenance
• Allows setup RAID (Redundant Arrays of
  Independent Disk)

40
NT After the Partition

• File systems can be created in two ways
• use format utility
• use the disk administrator utility (better
  choice)
• NTFS features
• partitions smaller than about 512 MB take up more
  overhead than FAT
• slightly more CPU intensive

41
UNIX Information Nodes (Inodes) Design
42
UNIX File System

• The UNIX File System (UFS) uses information
  nodes, or inodes
• Inode 0 contains the root of the file system
• The file system is identified by the superblock
  which contains information about the layout of
  blocks, sectors, and cylinder groups on the file
  system
• The inode does not contain a filename
• Directory entries can point to the same inode
• A hard link makes it possible for file names to
  appear in several directories under several names

43
UNIX Directory Showing Multiple Entries Pointing
to the Same Inode
44
UNIX File System Path Entries
45
Mounting

• A Path starts out with /, which indicates root
  directory
• The mount command maps the root inode of another
  file system onto the empty directory
• Mount command has several options
• shows no parameter results in a printout of the
  disks that are currently mounted
• shows the name of the partition and the path on
  which it was mounted

46
UNIX Drive Mount Path
47
UNIX Special Features

• Case-sensitivity (must type file names exactly as
  they appear)
• There are two types of devices
• A raw device has no logical division in blocks
• A block device does have logical division
• Partitions of all disks will appear as devices
  which are kept in the /dev or /devices directory
• Symbolic link is merely a pointer to a file it
  can point to a file that doesnt exist

48
UNIX Features

• Write command saves the label to the disk
• Print partition table command in fdisk or format
• File System Checker (fsck) operates when you
  start up UNIX to verify the integrity of the
  superblock, the inodes, all cluster groups, and
  all directory entries
• UFS file system can be up to 4 GB in size

49
The Macintosh File System

• Macintosh Filing System (MFS) keeps track of 128
  documents, applications, or folders
• Hierarchical Filing System (HFS) like FAT16, HFS
  divides a volume into units called allocation
  blocks

50
Macintosh Operating System 8.1

• Referred to as HFS, like Windows NT (NTFS) in
  that it increases the number of allocation blocks
  per volume
• The first 2 sectors of the formatted disk are
  boot blocks in the volume information block
• The catalog b-tree is a list of all files in the
  volume,
• Catalog b-tree tracks the filename, logical
  location, folder structure and physical location

51
More About Macintosh 8.1

• It supports medium filenames (up to 31
  characters)
• Rather than extensions, it uses type codes and
  creator codes
• Files contain two parts
• data fork contains frequently changed information
• resource fork contains fixed information

52
Mac Simple Text Resources, as Seen Through ResEdit
53
Macintosh First Aid

• Mac OS ships with two basic disk utilities
• Disk First Aid - which repairs minor hard drive
  problems
• Drive setup - which formats and partitions IDE
  and SCSI hard drives
• Sherlock Program searches disks for filenames and
  text within files

54
Mac OS 8.5s Sherlock Search Utility
55
Chapter Summary

• Chapter Three
• Gives an overview of the basic functions of all
  file systems
• Compares the Windows 95/98 file system with the
  older DOS/Windows 3.1 file systems
• Describes the fundamental features of the UNIX
  file system
• Describes the basics of the Macintosh file system