Transcript Presentation

3
File Systems
Guide to Operating Systems
Second Edition
Chapter 3
1
3
Objectives
After reading this chapter and completing the
exercises you will be able to:
• Understand the basic functions common to all file
systems
• Explain the design of the Windows 95 (FAT16)
and Windows 95, Windows 98, and Windows Me
(FAT32) file systems
Chapter 3
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Objectives
After reading this chapter and completing the
exercises you will be able to:
• Describe the Windows NT, Windows 2000, and
Windows XP file system (NTFS)
• Describe the design of the UNIX file system
• Describe the basics of the Macintosh file system
Chapter 3
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Understanding File System Functions
• A file system is a design for storing and managing files on
storage media
• The file systems used by personal computer operating
systems perform the following general functions:
– Enable files to be organized through directories and folders
– 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
– Enable error recovery or prevention
Chapter 3
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Understanding File System Functions
• The overall purpose of a file system is to create a
structure for filing data
• A file is a set of data that is grouped in some logical
manner, assigned a name, and stored on the disk
• The data contained in files can be text, images, music
and sounds, video, or Web pages for the Internet
• But no matter what kind of data is stored in the file
system, it must be converted into digital format—a
series of 1s and 0s, or electrical signal “ons” and
“offs” —that the computer understands
Chapter 3
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Understanding File System Functions
• There must be a way to write digital information
onto disk, track it, update it when necessary,
and call it back when the user, or a program
under the user’s control, wants it
• To achieve all this, the operating system
typically groups disk sectors in some logical
way, creates a record of this structure, and
builds a directory to track the type of data
stored in each file
Chapter 3
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A File System
Chapter 3
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Understanding File System Functions
• In addition to the names of files and where to find
them on the disk, directories also store the
following information:
– Date and time the directory or file was created (a
timestamp for that directory or file)
– Date and time the directory or file was last modified
(another form of timestamp)
– Directory or file size
– Directory of file attributes, such as security information,
or if the directory or file was backed up
Chapter 3
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Understanding File System Functions
• Figure 3-2
illustrates some
of the
information that
is stored for a
file in Windows
XP, which can be
displayed using
Windows
Explorer or My
Computer
Chapter 3
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Designing a Directory Structure
• For users, one of the most important features
of a file system is the ability to store
information according to a pattern of
organization that is enabled by the use of
directories
• In the early Windows systems and UNIX
systems, files are organized by directories,
while in later Windows versions and the Mac
OS, these are called folders
Chapter 3
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Designing a Directory Structure
• Directories and folders can be organized in a
hierarchy that is similar to a tree structure
• Some personal computer users keep most of
their files in the computer’s primary level or
root directory, or they load all application
software into a single directory
Chapter 3
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Designing a Directory Structure
• When you design a directory structure consider
directories for the following:
– Operating system files
– Software applications
– Work files, such as word processing, graphics,
spreadsheets, and database files
– Public files that you share over the network
– Utilities files
– Temporary files
Chapter 3
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Designing a Directory Structure
• The folder structure from the root might be as follows:
– Winnt for the system files
– Program Files for general software and utilities
– Documents and Settings for work files such as spreadsheets
and Word documents
– Shared for spreadsheets that are shared over the network
– Forms for specific types of forms used by the legal forms
software
– Inetpub for Web pages
• Each major folder has subfolders to keep grouped files or
applications software separate
Chapter 3
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Sample Folder Structure
for a Windows-based System
Chapter 3
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Designing a Directory Structure
•
For UNIX systems, such as Red Hat Linux, a typical directory (or
folder) structure is as follows:
– bin for user programs and utilities (binary files)
– lib for libraries
– usr for user files and programs
– var for files in which content often varies or that are used only
temporarily
– tmp for files used only temporarily
– dev for devices
– mnt for floppy drives, CD-ROM drives, and other removable media that
can be mounted
– Etc for system and configuration files
– sbin for user programs and utilities (system binary files)
– home for users’ home directories (or folders)
– proc for system resource tracking
Chapter 3
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Designing a Directory Structure
• In the Mac OS, the default folder structure
from the root includes:
– Applications for software applications
– System Folder for system files
– Library for library files (such as fonts)
– Users for user accounts
– Documents for documents
Chapter 3
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Disk Storage
• When a hard disk is delivered from the manufacturer, it is
low-level formatted
• A low-level format is a software process that marks the
location of disk tracks and sectors
• Every disk is divided into tracks, which are like several
circles around a disk
• Each track is divided into sections of equal size called
sectors
• Figure 3-4 illustrates a hard disk divided into tracks and
sectors
Chapter 3
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Disk Tracks and Sectors
Chapter 3
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Block Allocation
• The operating systems discussed in this book
use a method called block allocation to keep
track of where specific files are stored on the disk
• With block allocation the disk is divided into
logical blocks (in MS-DOS and Windows these are
called clusters), which are in turn mapped to
sectors, heads, and tracks on the disk
• The data regarding block allocation is stored on
the disk itself, using two techniques
Chapter 3
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Block Allocation
• One technique uses a fixed portion of the disk to
store this data, such as the FAT (file allocation
table) file system used by MS-DOS and supported
by all versions of Windows
• The other technique uses various locations on
the disk to store a special type of file that is used
for directory and file allocation information, such
as the New Technology File System (NTFS) and
the UNIX file systems
Chapter 3
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Partitions
• Before a file system can be placed on a hard disk,
the disk must be partitioned and formatted
• Partitioning is the process of blocking a group of
tracks and sectors to be used by a particular file
system, such as FAT or NTFS
• After a disk is partitioned, it must be high-level
formatted (usually referred to as just formatted)
so that the partition contains the disk divisions
and patterns needed by a particular operating
system to store files
Chapter 3
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Partitions
•
Figure 3-5
illustrates a
Windows 2000
system that has
multiple partitions
(FAT, NTFS, and
compact disk file
system (CDFS))
used for
segmenting data
on two hard disks
and a CD-ROM
drive
Chapter 3
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Partitions
• Partitioning can typically be done only on hard
disks or large removable disks
• Floppy disks and other low-capacity media do not
support partitioning because there simply isn’t
enough room on these low-capacity disks to
make partitioning practical
• On systems in the IBM/Intel PC hardware
architecture, typically there is room to store
information for up to four partitions on each disk
Chapter 3
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Partitions
• This area is known as the partition table in MSDOS, Mac OS, and Windows, and the disk label
in UNIX
• In addition to the disk label and partition table,
there is another piece of disk reserved, known
as the boot block in UNIX, or the Master Boot
Record (MBR) in MS-DOS and Windows
• This area hold a tiny program used to begin
booting an operating system from a disk
Chapter 3
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The Basic MS-DOS File System
• The first Microsoft file system, called the file
allocation table (FAT) file system started with MS-DOS
in the early eighties, and later versions of FAT are in
many ways similar to the earliest version
• FAT uses a file allocation table to store directory
information about files, such as filenames, file
attributes, and file location
• MS-DOS versions prior to 4.0 use the FAT12 file
system in which the maximum size of a file system is
32 MB
Chapter 3
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The Basic MS-DOS File System
• Beginning with MS-DOS 4.0, the FAT16 file
system is used, in which the maximum size of a
volume is 4 GB, and the maximum size for a file is
2 GB
• Another important characteristic of FAT is its use
of “8.3” filenames, which can be up to eight
characters long, followed by a period and an
extension of three characters, such as
Filename.ext
Chapter 3
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Partitioning
• The FAT file system supports two partitions per hard
drive, a primary partition and a secondary partition
• The secondary partition may then be divided further
into a maximum of three logical drives
• Each of these four possible logical drives can hold an
individual MS-DOS file system
• Although 26 drive definitions are technically possible,
MS-DOS reserves drive A: and B: for floppy drives,
practically limiting the number of hard drives
(including logical drives) to 24
Chapter 3
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Partitioning
Chapter 3
•
Each MS-DOS file
system is assigned a
letter followed by a
colon: A:, B:, C:, and
so on through Z:
•
Typically, C: is
reserved for the first
hard disk or
removable disk file
system (and is
normally the system
that contains the boot
partition)
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3
Partitioning
• If you start a computer in MS-DOS, you can use
the fdisk utility to look at the contents of the
partition record
• When the fdisk command is issued, a menu
appears, as shown in Figure 3-7
• You can choose option 4 from the menu in Figure
3-7 to see what partitions are on the disk
• This will give you a short overview, as shown in
Figure 3-8
Chapter 3
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Partitioning
Chapter 3
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Partitioning
• In the leftmost column, you see the partition number
and, if applicable, the drive letter associated with the
partition
• In the Status column, you see that one partition is
marked A, which stands for active
• When the computer is started, the BIOS looks at the
partition record, find the active partition (the partition
currently used to store data, and from which the
computer boots), and looks at the file system inside
that partition to start the operating system
Chapter 3
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Partitioning
• The Volume Label column shows the name of the file
system in the partition
• The Mbytes column represents the size of the partition in
megabytes
• Finally, the Usage column indicates how much of the total
available disk space is consumed by the file system
• You can use the other functions of the fdisk program to
delete or add partitions to the drives in your system
• To remove a partition, select option 3 from the fdisk menu,
which presents you with another menu for selecting which
partition you wish to remove
Chapter 3
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Partitioning
• With a new system called large block allocation (LBA), it
is now possible to make file systems much larger than
512 MB under MS-DOS
• LBA translates larger logical blocks to smaller ones for
support of larger physical disks
• However, the disk controller and disk must support LBA,
and they must be configured for LBA
• The trick to LBA is that MS-DOS is told that the sector
size of the hard disk is greater than 512 bytes per sector,
which results in the ability to have much larger file
systems
Chapter 3
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Formatting
• In MS-DOS (and in many Windows versions), the
file system is placed on the partition using the
format command
• This command writes all of the file system
structure to the disk
• In the case of a floppy disk, it uses the first sector
of the disk as the boot block
• As with many system-level commands, format
includes several additional switches that modify
precise program operation
Chapter 3
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format Command Switches
Chapter 3
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Formatting
• Command lines frequently use switches (extra
code) to change the way a particular command
operates
• The boot block is placed in the first sector on the
disk
• Next comes the root directory, where the system
stores file information, such as name, start
cluster, file size, file modification date and time,
and file attributes (file characteristics such a
Hidden, Read-only, Archive, and so on)
Chapter 3
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Formatting
• The root directory on every partition is a fixed
size that can contain a maximum of 512
entries in FAT16 (and unlimited entries in
FAT32)
• When a file is stored to disk, its data is
written in the clusters on the disk
• The filename is stored in the directory, along
with the number of the first cluster in which
the data is stored
Chapter 3
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Formatting
• When the operating system fills the first
cluster, data is written to the next free cluster
on the disk
• When a file is completely written to the disk,
the FAT entry for the final cluster is filled with
all 1s, which means end of file
• At this time, the directory entry for the file is
updated with the total file size
• This is commonly referred to as the “linkedlist” method
Chapter 3
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Formatting
• Clusters are of a fixed length, and if a file does
not exactly match the space available in the
clusters it uses, you can end up with some
unused space at the end of a cluster
• Unusable spots are marked in the FAT as bad
clusters, and these areas are never used for file
storage
• Formatting a disk removes all data that was on
the disk because you lost the directory and FAT
data needed to get to the data
Chapter 3
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Formatting
• On disks that have never been formatted, the
format command writes new sector and track
markers on the disk
• The format process on a hard disk is the
same as on a floppy disk, with two exceptions
• The first is related to the size of each entry in
the FAT table, which is 16 bits long on any
disk larger than 16 MB
• The second difference is in the cluster size
Chapter 3
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Hard Disk Cluster Reference
Chapter 3
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Formatting
• The FAT tables and
root directory are
found at the
beginning of each
partition, and they are
always at the same
location
• Each item in a
directory consists of
32 bytes
Chapter 3
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Formatting
• In each entry, information about the file is stored,
including the filename, the file change date and the
file size and the file attributes
• Apart from the filename, each directory entry also
contains some status bits that identify the type of
filename contained in each entry
• The status bits in use are Volume, Directory, System,
Hidden, Read-only, and Archive
• The Volume bit indicates a file system volume label, or
a nickname for the file system
Chapter 3
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Formatting
• The attrib command can be used to look at or set these
attributes
• Typing attrib in a directory shows all of the attribute
settings for all the files, whereas typing attrib followed
by a filename shows only attributes specific to that file
Chapter 3
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The Windows 95/98/Me
FAT File Systems
• There are two versions of FAT that can be
used with Windows 95, 98, and Me,
depending on the version of Windows you are
running, and the size of the disk you are
using:
– FAT16, similar to the system used in MS-DOS/Win
3.x
– FAT32, a new system introduced in Windows 95,
release 2 (OSR2)
Chapter 3
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Windows 95/98/Me FAT16
• In Windows 95, there is support for long filenames
(LFNs)
• A filename in the Windows 95 file system:
– Can contain as many as 255 characters
– Is not case sensitive
– Cannot include spaces and characters such as “/\[ ] :;=, (this
applies to both 8.3 filenames and LFNs)
• Since LFN characters are stored in Unicode, a coding
system that allows for representation of any character in
any language, it is possible to use any character known
to Windows in a filename
Chapter 3
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Windows 95/98/Me FAT16
• The advantage of LFNs and Unicode is that LFNs
can be read by Mac OS and UNIX systems
• Normally, letters and digits are represented by
ASCII (American Standard Code for Information
Interchange) values
• The problem with this standard is that it uses an
entire byte to represent each character, which
limits the number of characters that can be
represented to 255
Chapter 3
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Windows 95/98/Me FAT16
• This is not enough to handle all the characters
needed to represent world languages, including
several different alphabets (Greek, Russian,
Japanese, and Hindi, for example)
• ASCII deals with this problem by employing
different character sets, depending on the
characters you’re trying to represent
• Unicode is a 16-bit code that allots two bytes for
each character, which allows 65,536 characters to
be defined
Chapter 3
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Windows 95/98/Me FAT16
• Two advantages of FAT16 are that, like FAT12, it is
a simple file system supported by many small
computer operating systems, and it has a low
operating system overhead
• The disadvantages are that FAT16 become
corrupted over time as files are spread among
disjointed allocation units (clusters) and pointers
to each unit are lost, and FAT16 does not offer
many file or directory security or auditing options
Chapter 3
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FAT32
• To accommodate the increasing capacities of hard
disks, and avoid the problem of cluster size, the
second release of Windows 95 (OSR2) introduced an
improved FAT file system called FAT32
• FAT32 shares characteristics of FAT16 for Windows 95
• FAT32 allows partitions of up to 2 TB (theoretically);
blocks can be allocated with clusters as small as 8
KB, and the maximum file size is raised to 4 GB
Chapter 3
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FAT32
• FAT32 works by using many bits per FAT
allocation unit, and is therefore incompatible with
other operating systems such as MS-DOS and
Windows NT
• However, it is compatible with Windows 2000 and
XP
• You can choose the FAT32 file system when the
Windows 95/98 fdisk utility is run, but
unfortunately, the utility does not simply ask if
you wish to use FAT32
Chapter 3
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FAT32
• DO NOT use
FAT32 if you
plan to access
your hard disk
from MS-DOS
or Windows NT
because it is
not compatible
with these
systems
Chapter 3
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Windows 95/98/Me File System Utilities
• The fdisk and format
utilities in Windows
95, 98, and Me work
identically to those in
MS-DOS
• There are now also
graphical equivalents
of these tools that you
can launch from the
Windows user
environment, such as
the Windows 95
format tool shown in
Figure 3-11
Chapter 3
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Windows 95/98/Me File System Utilities
•
Sometimes disk performance is affected by corrupted files, or
when the file allocation table loses pointers to certain files
•
You can correct these problems in Windows 95 and maintain the
integrity of the data by periodically running the “Checkdisk”
utility, called chkdsk, by clicking Start, clicking Run, entering
chkdsk, and clicking OK
Chapter 3
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Windows 95/98/Me File System Utilities
• When you run chkdsk in Windows 98 and Windows
Me, the utility does not perform a true disk check, but
instead reports information about the volume serial
number, total disk space, free disk space, distribution
of allocation units, and lower memory allocation
(under 640 KB)
• ScanDisk is another checking utility, but it is a little
more advanced
• It has a nicer, menu-driven user interface, and it can
do a surface scan to determine whether you have
media problems on a disk
Chapter 3
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Windows 95/98/Me File System Utilities
• ScanDisk can
also copy to
another disk
the files it is
about to
manipulate, a
useful
precautionary
step to avoid
inadvertently
losing files or
data
Chapter 3
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Windows 95/98/Me File System Utilities
• Windows 95, 98, and Me also have a built-in disk
defragmenting tool
• When one of these operating systems writes a file
to disk, it looks for the first place in the first
empty FAT location and uses the cluster indicated
there
• To start the disk defragmenter, click Start, point
to Programs, point to Accessories, point to
System Tools, and click Disk Defragmenter
Chapter 3
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Windows 95/98/Me File System Utilities
• The Disk Defragmenter can also be automatically
started using the Scheduled Tasks tool
• In general, it is wise to defragment disks once a
month for medium-use systems, and once a week
for high-use systems
• It is VERY IMPORTANT that no other programs
are running while the Disk Defragmenter program
is running
Chapter 3
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Windows 98 Disk Defragmenter
Chapter 3
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The Windows NT/2000/
XP/.NET File Systems
• Windows NT supports two types of file
systems: the extended FAT16 system used
by Windows 95, and the NTFS up through
version 4 (for Windows NT 4.0)
Chapter 3
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Extended FAT16
• The extended FAT16 file system under Windows
NT/2000/XP/.NET has the same functionality as
the FAT16 system under Windows 95, and it is
possible to have multiple operating systems on
one disk (called dual-boot or multiboot systems)
with the FAT16 file system
• POSIX stands for Portable Operating System
Interface, a set of standards designed to
guarantee portability of applications among
different operating systems
Chapter 3
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FAT32
• Windows 2000, XP, and .NET Server all
support FAT32, which is the same file system
that is used in Windows 95 OSR2, Windows
98, and Windows Me
• Sometimes users choose to employ FAT16 or
FAT32 because they are familiar with these
file systems, or they have dual-boot systems,
such as a system with Windows XP and
Windows 98
Chapter 3
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FAT32
• Any Windows NT, 2000, XP, or .NET Server
system can be converted from FAT16 or
FAT32 to NTFS, either during installation or at
a later date
• Converting from FAT16 or FAT32 to NTFS can
take many hours on a volume that is over 1
GB, and the conversion process may appear
hung, even though it is not
Chapter 3
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NTFS
• Four important advantages of NTFS
compared to FAT16 and FAT32 are:
– Ability to compress file and directory contents
on the fly
– Better recoverability and stability
– Less disk fragmentation
– Local file and folder-level security
Chapter 3
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NTFS
• The basic features initially incorporated into NTFS 4
include:
– Long filenames (LFN)
– Built-in security features
– Better file compression than FAT
– Ability to use larger disks and files
– File activity tracking for better recovery and stability than FAT
– POSIX support
– Volume striping and volume extensions
– Less disk fragmentation than FAT
Chapter 3
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NTFS
• NTFS enables the use of LFNs that are compatible with
LFN FAT filenames
• If an LFN is used in NTFS, that file can be copied to a
FAT16 or FAT32 volume, and the filename remains intact
• As a full-featured network file system, NTFS is equipped
with security features that meet the U.S. government’s
C2 security specifications
• C2 security refers to high-level, “top secret” standards
for data protection, system auditing, and system access,
which are required by some government agencies
Chapter 3
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NTFS
• NTFS can be scaled to accommodate very large
files, particularly for database applications
• A Microsoft SQL Server database file might be 20
GB or larger
• Another NTFS feature is its ability to keep a log of
file system activity
• NTFS supports POSIX standards to enable
portability of applications from one computer
system to another
Chapter 3
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NTFS
• Windows 2000 follows the POSIX 1 standard, which
includes case-sensitive filenames and use of multiple
filenames
• An important volume-handling feature of NTFS is the
ability to create extensions on an existing volume,
such as when new disk storage is added
• Last, NTFS is less prone to file corruption than FAT, in
part because it has a “hot fix” capability, which means
that if a bad disk area is detected, NTFS automatically
copies the information from the bad area to another
disk area that is not damaged
Chapter 3
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NTFS
• In addition to the NTFS 4 features already
described, NTFS 5 adds several new features:
– Ability to encrypt files
– No system reboot required after creating an extended
volume
– Ability to reduce drive designations
– Indexing for fast access
– Ability to retain shortcuts and other file information
when files and folders are placed on other volumes
– Ability to establish disk quotas
Chapter 3
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NTFS
• With NTFS 5, files can be encrypted so that their
contents are available only to those granted
access
• Also, volume extensions can be set up without
the need to reboot the system (in NTFS 4 you
must reboot after adding an extension onto an
existing volume
• A new technique called Distributed Link Tracking
is available in NTFS 5 so that shortcuts you have
created are not lost when you move files to
another volume
Chapter 3
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NTFS
• The way NTFS keeps track of files and clusters
is a little different from the FAT file system
• Rather than using a structure of FAT tables and
directories, NTFS uses a Master File Table
(MFT)
• Like the FAT tables and directories, this table is
located at the beginning of the partition
• When a file is made in NTFS, a record for that
file is added to the MFT
Chapter 3
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NTFS
• The MFT record reflects the sequence of
clusters that a file uses
• It is also possible to have multiple filenames
that refer to the same file, a technique known
as hard linking
• Table 3-5 provides a comparison of the most
frequently used Microsoft file systems—
FAT16, FAT32, and NTFS
Chapter 3
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FAT16, FAT32, and NTFS Compared
Chapter 3
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3
NTFS Utilities
• Windows NT, 2000, XP, and .NET Server all
come with the chkdsk utility, which is much
more robust than in other Windows operating
systems
• Because chkdsk is more robust, these
operating systems do not come with ScanDisk
• Windows NT does not come with a disk
defragmenter tool, so this must be purchased
from a third-party vendor
Chapter 3
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3
Chkdsk Switch Options
Chapter 3
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3
NTFS Utilities
•
Windows 2000, XP, and .NET Server all have Disk Defragmenter,
which is initiated by clicking Start, pointing to Programs, pointing
to Accessories, and clicking Disk Defragmenter
Chapter 3
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3
NTFS Utilities
• Care should be taken to use only utilities
designed to work with NTFS; serious damage can
occur if other utilities are used
• When you upgrade Windows NT Server 4.0 to
Windows 2000 or Windows .NET, the current
NTFS disk partitions are automatically converted
to basic disks, which use traditional NTFS disk
management techniques, with a limited number of
volumes on one disk
Chapter 3
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3
CDFS and UDF
• The Universal Disk Format (UDF) file
system is also used on CD-ROM and large
capacity Digital Video Disk-Read Only
Memory (DVD-ROM) media, which are
used for huge file storage to
accommodate movies and games
Chapter 3
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The UNIX File System
• The UNIX file system works a little differently
from anything discussed up to this point
• “UNIX file system” is really a misnomer
• In Linux, the extended file system (ext or ext fs) is
native and installed by default
• Ext provides an advantage over all other file
systems that can be used with Linux because it
enables the use of the full range of built-in Linux
commands, file manipulation, and security
Chapter 3
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File Systems Supported by UNIX
Chapter 3
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3
File Systems Supported by UNIX
Chapter 3
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3
The UNIX File System
•
The main difference
between native UNIX
file systems, such as
ext3 and ufs, and
those covered earlier
in the chapter, lies in
the way information is
physically stored on
the disk
•
The ufs UNIX file
system (and also
ext/ext2/ext3) uses
the concept of
information nodes, or
inodes
Chapter 3
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The UNIX File System
• Each inode can store some information about a
file on the file system
• The information stored on an inode identifies: the
inode number, the owner of the file, the group in
which the file is placed, the size of the file, the
date the file was created, the date the file was last
modified and read, the number of links to this
inode, and information regarding the location of
the blocks in the file system in which the file is
stored
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The UNIX File System
• Blocks are typically 4096 or 8192 bytes in size,
but the file system is capable of dividing these
blocks, if required
• Groups of blocks for cylinder groups and large
files are allocated cylinder groups at the same
time
• A block can be divided by two repeatedly until the
smallest fractional block size is reached, which is
typically equal to the size of a single sector on
the disk
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The UNIX File System
• The superblock contains information about the layout
of blocks, sectors, and cylinder groups on the file
system
• This information is the key to finding anything on the
file system, and it should never change
• A UNIX system can have many file systems
• Unlike the MS-DOS/Windows environment, where
each file system must have a letter of the alphabet
assigned to it to enable access, UNIX mounts file
systems as a sub-file system of the root file system
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Multiple Directory Entries
Pointing to the Same Inode
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The UNIX File System
• In UNIX, all file systems are referred to by a path
• Then, using the mount command, the UNIX
operating system is told to map the root inode of
another file system onto the empty directory
• The mount command has several options: typical
it without parameters results in a display of the
disks that are currently mounted
• As we already mentioned, a directory is nothing
more than a special file
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UNIX File System Path Entries
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UNIX Drive Mount Path
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The UNIX File System
• There are several other special files in the UNIX
file system
• Disks themselves, are, for example, referenced
by a special inode called a device
• There are two types of devices, raw devices
and block devices
• A raw device has no logical division in blocks,
whereas a block device does
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The UNIX File System
• Every device the UNIX computer uses must
be represented by a device inode, whether it
is a disk, a serial port, or an Ethernet card
• There is another special feature of the UNIX
file system we should mention here, the
symbolic link
• If you want to link a directory entry to a file
that is on a different partition, you must use a
feature known as a symbolic link
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The UNIX File System
• This is a special file, which has a flag set in the
inode to identify it as a symbolic link
• As with all other operating systems discussed so
far, you first have to partition a disk to use the
UNIX file system
• The command used to partition the disk differs
slightly from one version of UNIX to another
• In most UNIX systems, either fdisk or format does
the job
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The UNIX File System
• Once a partition is made, it is time to create the
file system
• To do this, you must know the device name of the
partition on which you wish to create a file
system
• This name can be obtained from the print
partition table command in fdisk or format
• UNIX is very picky when it comes to file system
consistency
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The UNIX File System
• If it finds problems on the file system in the inodes,
superblock, or directory structures, it will shut
down
• Typically, ufs file systems can be up to 4 GB in
size, but by using larger block sizes, the systems
can be made much larger
• Depending on the implementation of UNIX being
used, and the exact ufs version in use, it is
possible to create file systems in excess of 32
exabytes
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UNIX File System Commands
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UNIX File System Commands
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The Macintosh File System
• The original Macintosh Filing System (MFS) of
1984 was limited to keeping track of 128
documents, applications, or folders
• As larger disks became available, the need for
directories and subdirectories became obvious,
and Apple responded with the Hierarchical Filing
System (HFS) in 1986
• Like FAT16, HFS divides a volume (the Mac term
for a disk or disk partition) into, at most, 216
(65,536) units
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The Macintosh File System
• On PC systems,
these units are
called clusters
or allocation
units
• On the Mac,
they are called
allocation
blocks, but the
principle is the
same
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The Macintosh File System
• The first two sectors of a Mac-formatted disk are the
boot sectors, or boot blocks in Macintosh terminology
• The boot blocks identify the filing system, the names
of important system files, and other important
information
• The boot blocks are followed by the volume
information block, which points to other important
areas of information, such as the location of the
system files, and the catalog and extents trees
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The Macintosh File System
• The catalog b-tree is the list of all files on the volume
• The extents b-tree keeps track of the location of the
file fragments, or extents
• In terms of filename length, the Mac OS has always
supported what might be called “medium” filenames
of up to 31 characters in length
• UNIX and Windows operating systems use filename
extensions such as .txt and .gif to identify file types
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The Macintosh File System
• The Mac uses invisible type codes and creator
codes
• As an example, files created with Apple’s
SimpleText text editor have a type code of TEXT,
and a creator code of ttxt
• The type and creator codes facilitate the Mac’s
use of icons
• One way in which Macintosh files are unique is
that Mac files an contain two parts, or forks: the
data fork and the resource fork
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The Macintosh File System
• The data fork contains frequently changing
information (such as word processing data), while the
resource fork contains information that is fixed (such
as a program’s icons, menu resources, and splash
screens)
• Apple’s free ResEdit utility can edit file resources
• Using ResEdit, a programmer can modify a program’s
version number, splash screens, default memory
allocation, icons, menu items, window resources,
dialog text, and many other properties
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The Macintosh File System
• The fact that Mac
files have
invisible type and
creator codes and
two forks can
create problems
when storing files
on non-Macintosh
servers, or
transferring files
over the Internet
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The Macintosh File System
• The need to store Mac files on non-Mac
computers has led to several Mac file formats for
bulletin board services, online services, and the
Internet
• One of these formats is MacBinary, which joins
the two forks into one, and safely stores the type
and creator codes and finder flags
• Like uuencode, BinHex transforms all files into
seven-bit files using the ASCII character set
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The Macintosh File System
• Like MacBinary, BinHex preserves the two forks,
the type and creator codes, and the finder flags
• BinHex files can be identified by the .hqx filename
extension
• Apple’s equivalent of the UNIX link and Windows
shortcut is the alias, introduced in System 7.0 in
1991
• Files, folders, applications, and disks can be
aliased
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The Macintosh File System
• The Mac OS ships with two basic disk utilities:
Disk First Aid and Drive Setup
• Drive Setup, a replacement for the older Apple HD
Setup, formats and partitions Apple IDE and SCSI
hard drives
• Drive Setup checks the hard drive for a ROM that
is present in drives shipped with Apple
computers
• Most versions of the Mac OS include a basic find
file utility
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The Macintosh File System
•
Mac OS 8.5 takes this one step further with the Sherlock program
•
Sherlock can search disks for filenames and text within files
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Summary
• For the user, files are the “bread and butter” of an
operating system
• Besides containing the operating system kernel,
files hold documents and programs on which
users rely
• The file systems used by early Microsoft
operating systems include FAT12 and FAT16
• In these file systems, the file allocation table
(FAT) file system creates a file allocation table to
store information about files
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Summary
• The fdisk and format utilities are used with all
versions of FAT file systems to partition and
format disks, while the chkdsk and ScanDisk
utilities give information about files and disks,
and check for disk and file integrity
• The FAT32 file system was introduced in the
second release of Windows 95, and is also used
in Windows 98 and Windows Me
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Summary
• The native file system for Windows NT, 2000, XP,
and .NET is called NTFS, but FAT32 is also
supported by Windows 2000 and XP, while FAT16
is supported by Windows NT, 2000, and XP
• NTFS is a more stable and secure file system
than FAT, and in general, can handle larger disk
and file sizes
• UNIX file systems use information nodes (inodes)
to organize information about files
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Summary
• A UNIX system can have many file systems
mounted as subdirectories of the root
• The Macintosh OS uses the Hierarchical Filing
System (HFS)
• Like FAT, HFS divides a disk or disk partitions
(called a volume) into allocation units called
allocation blocks
• Unlike FAT, HFS has always allowed the use of
relatively long filenames
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