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Disk Structures

Disk Structures. Formatting a Disk. Two parts to formatting a disk: Low-level (physical) formatting High level (logical) formatting Low-level (physical) formatting: Sequentially numbers tracks and sectors Identifies each track and sector Disk is physically prepared to hold data

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Disk Structures

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  1. Disk Structures

  2. Formatting a Disk Two parts to formatting a disk: • Low-level (physical) formatting • High level (logical) formatting Low-level (physical) formatting: • Sequentially numbers tracks and sectors • Identifies each track and sector • Disk is physically prepared to hold data High-level (logical) formatting: • Determines how OS uses a disk • Builds structure to keep track of location of files • Done so files can be stored and retrieved Disk Structures (31 slides)

  3. Formatting a Disk Windows XP Professional monitors status of all disk data sectors One or more sectors are combined into logical units called clusters or allocation units Cluster (allocation unit): • Smallest unit that OS can work with Cluster overhang: • Wasted space on the disk Disk Structures (31 slides)

  4. Master Boot Record & Boot Sector Disk Structures (31 slides)

  5. Master Boot Record & Boot Sector Master boot record (MBR): • First part of hard disk • Locates bootable partition of hard disk and gives control over to it Boot sector: • First sector on logical drive • Has table of drive’s characteristics • Has bootstrap loader program All disks (including non-system disks) have a boot sector Disk Structures (31 slides)

  6. Master Boot Record & Boot Sector FAT non-system error messages: • Non-system disk or disk error • Replace disk and press any key when ready NTFS non-system error messages: • Invalid partition table • Error loading operating system • Missing operating system Floppy disk non-system error messages: • NTLDR is missing • Press any key to restart Windows uses boot sector to identify the type of disk. Disk Structures (31 slides)

  7. FAT16, VFAT, and FAT32 Disk Structures (31 slides)

  8. FAT15, VFAT & FAT32 FAT ‘s formatting program creates: • Boot record • File Allocation Table (2 copies) • Root directory Logical Structure  of a Disk Disk Structures (31 slides)

  9. FAT15, VFAT & FAT32 • FAT is a map of disk’s data clusters • FAT number indicates status of cluster (Numbers in FAT .. link clusters that belong to same file) Cluster Size and  Disk Size Disk Structures (31 slides)

  10. FAT15, VFAT & FAT32 FAT essential for : • Managing data • Following trail of clusters that make up a file VFAT maintains backwards compatibility and accommodates long file names. FAT32: • Enhancement of FAT file system • Introduced to overcome limitations of VFAT • Does not apply to floppy drives Disk Structures (31 slides)

  11. FAT15, VFAT & FAT32 Comparison of FAT and FAT32 Disk Structures (31 slides)

  12. FAT15, VFAT & FAT32 FAT32: • Movable Root Directory • Can be located anywhere on hard disk • Can use backup copy of FAT • Internal backup copy of some critical FAT data structures • Entries in Root Directory limited With smaller clusters: • Table smaller • Takes less time to locate/access file • Increases wasted disk space from cluster overhang FAT32 is best for many small files FAT is best for mostly large files Disk Structures (31 slides)

  13. The Root Directory Disk Structures (31 slides)

  14. The Root Diretory Root Directory: • Table that records information about each file on the disk • Changes in root directory table make Windows XP Professional compatible with older Windows and DOS programs • Root directory tells what is on the disk Disk Structures (31 slides)

  15. The FAT and the Root Directory Disk Structures (31 slides)

  16. The FAT and the Root Directory • FAT tells where data is on the disk • Number is FAT points to next cluster that holds data in file • EOF (end-of-file) marker indicates there is no more data in file Disk Structures (31 slides)

  17. The FAT and the Root Directory The Root Directory and FAT Disk Structures (31 slides)

  18. The Data Portion or the Files Area Disk Structures (31 slides)

  19. The Data Portion or the Files Area • Largest part of disk is used for storing files • Space is allocated to files on an as-needed basis A file is written to a disk in: • Contiguous clusters or • Non-contiguous clusters Disk Structures (31 slides)

  20. Understanding the FAT and the Root Directory Disk Structures (31 slides)

  21. Understanding the FAT and the Root Directory Storing Files Disk Structures (31 slides)

  22. NTFS Disk Structures (31 slides)

  23. NTFS • File system used determines OS advanced features available to user • For disk security, performance, and efficiency use NTFS file system Advantages of NTFS: • Secure file system • Efficient storage of data • Faster file access • Better data recovery • Can compress files/assign disk quotas • Encryption of files Disk Structures (31 slides)

  24. Clusters and NTFS Disk Structures (31 slides)

  25. Clusters and NTFS NTFS: • Uses FAT cluster scheme for allocating data • Has less overhead NTFS Cluster Size Disk Structures (31 slides)

  26. Clusters and NTFS Structure of an NTFS Volume Disk Structures (31 slides)

  27. Master File Table (MFT) Disk Structures (31 slides)

  28. NTFS Master File Table (MFT) Master File Table (MFT): • Database of all files in system • Used by NTFS to track all files and directories in a volume • Dynamic Disk Structures (31 slides)

  29. NTFS Master File Table (MFT) MFT is different from FAT: MFT: • Adds security descriptor attribute to file system • Data in file considered to be attribute of file • Allows fast access to files • Eliminates file fragmentation • Attribute stored in MFT considered resident attribute • Any resident forced out to an extent is nonresident attribute Folders treated as files in NTFS: • Small folder – Index Root attribute • Folder entries will fit into MFT – new extent nonresident attribute called index buffer Disk Structures (31 slides)

  30. Deciding on a File System Disk Structures (31 slides)

  31. Deciding on a File System Formatting: • Floppy disk – always FAT file system • Hard disk – you decide • Can convert FAT to FAT32/NTFS • Cannot convert FAT32/NTFS to FAT Disk Structures (31 slides)

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