Chapter 3


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Chapter 3

  1. 1. Chapter 3: File Systems A Guide to Operating Systems: Troubleshooting and Problem Solving
  2. 2. Chapter Objectives <ul><li>Understand the basic functions of all file systems </li></ul><ul><li>Describe the major elements of the DOS and Windows 3.1/ 3.11 file system </li></ul><ul><li>Compare and contrast the Windows 95/ 98 file system (FAT16 and FAT32) with the older DOS/ Windows 3.1 file system </li></ul><ul><li>Describe the fundamental features of the UNIX file system </li></ul><ul><li>Describe the basics of the Macintosh file system </li></ul>
  3. 3. Understanding File System Functions <ul><li>Partition and format disks to store and retrieve information </li></ul><ul><li>Establish file naming conventions </li></ul><ul><li>Provide utilities for functions such as file compression and disk defragmentation </li></ul><ul><li>Provide for file and data integrity </li></ul><ul><li>Provide storage media management functions </li></ul>
  4. 4. A File System Metaphor
  5. 5. Data Files Contain <ul><li>Text </li></ul><ul><li>Images </li></ul><ul><li>Music </li></ul><ul><li>Sounds </li></ul><ul><li>Video </li></ul><ul><li>Web Pages for the Internet </li></ul>
  6. 6. Block Allocation <ul><li>Keeps track of where specific files are stored on disk </li></ul><ul><li>In DOS and Windows, these are clusters </li></ul><ul><li>Hard disk platter has two sides (read/ write head) </li></ul><ul><li>Clusters are mapped to sectors, heads, and tracks </li></ul><ul><li>Divided into logical blocks </li></ul><ul><li>Tracks that line up on platter are called cylinders </li></ul>
  7. 7. Block Allocation <ul><li>Two techniques are used to store data: </li></ul><ul><ul><li>A fixed portion of the disk is used (FAT) </li></ul></ul><ul><ul><li>Various locations on the disk are used (UNIX and NTFS) </li></ul></ul>
  8. 8. Partitions and Related Components <ul><li>Divides hard drive into sections </li></ul><ul><li>Creates multiple logical volumes that you assign drive letters to </li></ul><ul><li>Partition table (DOS, Mac OS, and Windows </li></ul><ul><li>Disk label in UNIX </li></ul><ul><li>Boot block in UNIX </li></ul><ul><li>Master boot record in Windows (MBR) </li></ul>
  9. 9. The DOS/Windows 3.1 File System <ul><li>Uses a file allocation table (FAT) file system </li></ul><ul><li>Use of 8.3 file names which can be up to 8 characters long followed by a period and an extension of 3 characters </li></ul><ul><li>With DOS prior 4.0, the maximum size of file system was 32 MB (FAT12) </li></ul><ul><li>With MS-DOS from 4.0, the maximum size was 2 GB (FAT16) </li></ul>
  10. 10. Partitioning <ul><li>The FAT file system supports two partitions per hard drive - a primary and a secondary partition </li></ul><ul><li>A secondary partition may be divided into a maximum of three logical drives </li></ul>
  11. 11. Sample DOS Partition Table Structure <ul><li>FDISK is used to modify partition information </li></ul>
  12. 12. MS-DOS FDISK Utility
  13. 13. FDISK Partition Information Screen
  14. 14. Formatting: Placing a file system on a partition <ul><li>Boot block contains information about disk (number of tracks and sectors per track) </li></ul><ul><li>Boot block contains small program to start operating system </li></ul><ul><li>In DOS use the format command </li></ul><ul><li>Writes all of the file system structure to disk </li></ul><ul><li>A floppy uses first sector as the boot block </li></ul>
  15. 15. FORMAT Command Switches
  16. 16. Root Directory and File Attributes <ul><li>Root directory contains the following: </li></ul><ul><ul><li>name, start cluster, file size, file modification date and time </li></ul></ul><ul><ul><li>every partition is a fixed size </li></ul></ul><ul><li>File attributes (characteristics) </li></ul><ul><ul><li>hidden, read only and archive </li></ul></ul>
  17. 17. Clusters <ul><li>Not fixed in length </li></ul><ul><li>If a file does not exactly match the disk space available in the cluster, there will be unused space at the end of cluster </li></ul><ul><li>Unused spots in FAT are marked as bad clusters </li></ul><ul><li>The largest possible partition in FAT is 4 GB </li></ul>
  18. 18. Hard Disk Cluster Reference
  19. 19. Typical FAT Directory Structure <ul><li>The FAT table and root directory are found at the beginning of each partition, and are always at the same location. </li></ul><ul><li>Each item in the directory consists of 32 bytes </li></ul>
  20. 20. Extensions <ul><li>SYS extension is generally the device driver </li></ul><ul><li>COM or EXE extensions are program files that the operating system can execute </li></ul><ul><li>BAT extensions are batch files of commands that can be executed as if they were typed on the keyboard </li></ul><ul><li>Filename and extension cannot contain spaces </li></ul>
  21. 21. ATTRIB Arguments and Switches
  22. 22. DOS File System Utilities <ul><li>CHKDSK checks the contents of directories and verifies the consistency of FAT tables </li></ul><ul><li>/F, for Fix allows you to correct problems </li></ul><ul><li>SCANDISK is a menu driven interface </li></ul><ul><li>Copies files it will manipulate to a disk </li></ul><ul><li>Conducts some of the same tasks as CHKDSK </li></ul>
  23. 23. Another DOS Utility <ul><li>Defragment - rewrites files to a disk so that they are contiguous </li></ul><ul><ul><li>Looks for empty FAT location and uses the cluster indicated </li></ul></ul><ul><ul><li>Continues to use the next empty cluster until no more free clusters are found </li></ul></ul>
  24. 24. More About Defragmentation <ul><li>The Disk Defragmenter utility maximizes access time and makes it faster to write new files to disk </li></ul><ul><li>Floppy disks do not need to be defragmented </li></ul><ul><li>The hard disk should be defragmented on a regular basis </li></ul>
  25. 25. Windows 95/ 98 File System <ul><li>FAT16 is similar to the system used in DOS/ Win 3.1 </li></ul><ul><li>FAT32 is a new system introduced in Windows 95, release B </li></ul><ul><li>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 </li></ul>
  26. 26. Windows 95/ 98 FAT16 <ul><li>File names may contain as many as 255 characters </li></ul><ul><li>File names are not case sensitive </li></ul><ul><li>File name can include spaces and several characters that 8.3 names cannot (./[]:;=) </li></ul>
  27. 27. DOS 8.3 Filenames versus Long Filenames (LFN)
  28. 28. Long Filenames (LFN) <ul><li>The LFN is stored by using a series of additional directory entries </li></ul><ul><li>It can contain up to 13 characters in upper or lower case </li></ul><ul><li>Unicode allows for representation of any character in any language </li></ul>
  29. 29. Long Filenames (LFN) <ul><li>Unicode is a 16-bit code </li></ul><ul><li>ASCII (American Standard Code for Information Interchange) uses an entire byte to represent each character </li></ul><ul><li>Limits number of characters represented to 255 </li></ul>
  30. 30. Long Filename Storage Scheme
  31. 31. FAT32 <ul><li>Gets around the problem of cluster size </li></ul><ul><li>Allows the partitions to be up to 8 GB </li></ul><ul><li>Blocks can be allocated with up to 8 KB </li></ul><ul><li>The maximum partition size will be raised to 32 GB </li></ul><ul><li>Don’t use FAT32 if you plan to access your hard disk from other operating systems </li></ul>
  32. 32. Windows 95/98 File System Utilities <ul><li>Windows 95/ 98 includes the capability to create compressed disk volumes </li></ul><ul><li>Windows 95 also has a defragmentation utility that will run from system scheduler </li></ul><ul><li>No other programs should be running while using the defragmentation utility </li></ul>
  33. 33. DEFRAG Utility
  34. 34. Windows NT File Systems <ul><li>Windows NT supports two types of file systems: </li></ul><ul><ul><li>The extended FAT16 system </li></ul></ul><ul><ul><li>The New Technology File System (NTFS) </li></ul></ul><ul><li>Both systems are Portable Operating System Interface (POSIX) compliant </li></ul>
  35. 35. New Technology File System (NTFS) Features <ul><li>Built-in security </li></ul><ul><li>Ability to use larger disks and larger files </li></ul><ul><li>Ability to compress file and directory contents on the fly </li></ul><ul><li>Better recoverability and stability </li></ul><ul><li>Less disk fragmentation </li></ul>
  36. 36. NTFS Numerical Equivalents
  37. 37. NTFS Default Cluster Sizes
  38. 38. Tracking Files and Clusters <ul><li>NTFS tracks files and clusters using a Master File Table (MFT) </li></ul><ul><li>The MFT is located at the beginning of the partition </li></ul><ul><li>The Boot sector is located ahead of the MFT </li></ul><ul><li>Normally the MFT takes up 1 MB </li></ul>
  39. 39. NT Disk Administrator <ul><li>NT Disk Administrator allows you to partition and format disks </li></ul><ul><li>Allows you to change disk and partition attributes </li></ul><ul><li>Performs disk maintenance </li></ul><ul><li>Allows setup RAID (Redundant Arrays of Independent Disk) </li></ul>
  40. 40. NT After the Partition <ul><li>File systems can be created in two ways: </li></ul><ul><ul><li>use format utility </li></ul></ul><ul><ul><li>use the disk administrator utility (better choice) </li></ul></ul><ul><li>NTFS “features” </li></ul><ul><ul><li>partitions smaller than about 512 MB take up more overhead than FAT </li></ul></ul><ul><ul><li>slightly more CPU intensive </li></ul></ul>
  41. 41. UNIX Information Nodes (Inodes) Design
  42. 42. UNIX File System <ul><li>The UNIX File System (UFS) uses information nodes, or inodes </li></ul><ul><li>Inode 0 contains the root of the file system </li></ul><ul><li>The file system is identified by the superblock which contains information about the layout of blocks, sectors, and cylinder groups on the file system </li></ul><ul><li>The inode does not contain a filename </li></ul><ul><li>Directory entries can point to the same inode </li></ul><ul><li>A hard link makes it possible for file names to appear in several directories under several names </li></ul>
  43. 43. UNIX Directory Showing Multiple Entries Pointing to the Same Inode
  44. 44. UNIX File System Path Entries
  45. 45. Mounting <ul><li>A Path starts out with /, which indicates root directory </li></ul><ul><li>The mount command maps the root inode of another file system onto the empty directory </li></ul><ul><li>Mount command has several options </li></ul><ul><ul><li>shows no parameter results in a printout of the disks that are currently mounted </li></ul></ul><ul><ul><li>shows the name of the partition and the path on which it was mounted </li></ul></ul>
  46. 46. UNIX Drive Mount Path
  47. 47. UNIX Special Features <ul><li>Case-sensitivity (must type file names exactly as they appear) </li></ul><ul><li>There are two types of devices: </li></ul><ul><ul><li>A raw device has no logical division in blocks </li></ul></ul><ul><ul><li>A block device does have logical division </li></ul></ul><ul><li>Partitions of all disks will appear as devices which are kept in the /dev or /devices directory </li></ul><ul><li>Symbolic link is merely a pointer to a file; it can point to a file that doesn’t exist </li></ul>
  48. 48. UNIX Features <ul><li>Write command saves the label to the disk </li></ul><ul><li>Print partition table command in fdisk or format </li></ul><ul><li>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 </li></ul><ul><li>UFS file system can be up to 4 GB in size </li></ul>
  49. 49. The Macintosh File System <ul><li>Macintosh Filing System (MFS) keeps track of 128 documents, applications, or folders </li></ul><ul><li>Hierarchical Filing System (HFS) like FAT16, HFS divides a volume into units called allocation blocks </li></ul>
  50. 50. Macintosh Operating System 8.1 <ul><li>Referred to as HFS+, like Windows NT (NTFS) in that it increases the number of allocation blocks per volume </li></ul><ul><li>The first 2 sectors of the formatted disk are boot blocks in the volume information block </li></ul><ul><li>The catalog b-tree is a list of all files in the volume, </li></ul><ul><li>Catalog b-tree tracks the filename, logical location, folder structure and physical location </li></ul>
  51. 51. More About Macintosh 8.1 <ul><li>It supports medium filenames (up to 31 characters) </li></ul><ul><li>Rather than extensions, it uses type codes and creator codes </li></ul><ul><li>Files contain two parts: </li></ul><ul><ul><li>data fork contains frequently changed information </li></ul></ul><ul><ul><li>resource fork contains fixed information </li></ul></ul>
  52. 52. Mac Simple Text Resources, as Seen Through ResEdit
  53. 53. Macintosh First Aid <ul><li>Mac OS ships with two basic disk utilities: </li></ul><ul><ul><li>Disk First Aid - which repairs minor hard drive problems </li></ul></ul><ul><ul><li>Drive setup - which formats and partitions IDE and SCSI hard drives </li></ul></ul><ul><li>Sherlock Program searches disks for filenames and text within files </li></ul>
  54. 54. Mac OS 8.5’s Sherlock Search Utility
  55. 55. Chapter Summary <ul><li>Chapter Three: </li></ul><ul><li>Gives an overview of the basic functions of all file systems </li></ul><ul><li>Compares the Windows 95/98 file system with the older DOS/Windows 3.1 file systems </li></ul><ul><li>Describes the fundamental features of the UNIX file system </li></ul><ul><li>Describes the basics of the Macintosh file system </li></ul>