disk structures. ctec 1102 formatting a disk two parts to formatting a disk: low-level (physical)...

Disk Structures

CTEC 110 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)

CTEC 110 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


CTEC 110 4

Master Boot Record & Boot Sector


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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


CTEC 110 6


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.


CTEC 110 7

FAT16, VFAT, and FAT32


CTEC 110 8

FAT15, VFAT & FAT32

FAT ‘s formatting program creates: Boot record File Allocation Table (2 copies) Root directory

Logical Structure of a Disk


CTEC 110 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 SizeNumber of Sectorsin a Cluster

Cluster Sizein Bytes

Cluster Sizein KB

3 1/2-inch 1.44 MB 1 Sector 512 1/2 KB

3 1/2-inch 2.88 MB 2 sectors 1,024 1KB

33 MB-64 MB 2 sectors 1,024 1KB

65 MB-128 MB 4 sectors 2,048 2KB

129 MB-256 MB 8 sectors 4,096 4KB

257 MB-512 MB 16 sectors 8,192 8KB

513 MB-1,024 MB 32 sectors 16,384 16KB

1,025 MB-2,048 MB 64 sectors 32,768 32KB


CTEC 110 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


CTEC 110 11

FAT15, VFAT & FAT32

Comparison of FAT and FAT32


CTEC 110 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 filesFAT is best for mostly large files


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The Root Directory


CTEC 110 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


CTEC 110 15

The FAT and the Root Directory


CTEC 110 16


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


CTEC 110 17


The Root Directory and FAT


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The Data Portion or the Files Area


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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


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Understanding the FAT and the Root Directory


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Understanding the FAT and the Root Directory

Storing Files


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NTFS


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

CTEC 110 23Disk Structures (31 slides)

CTEC 110 24

Clusters and NTFS


CTEC 110 25

Clusters and NTFSNTFS: Uses FAT cluster scheme for allocating data Has less overhead

NTFS Cluster Size

Partition Size Cluster Size in Bytes Sectors in a Cluster7 MB-512 MB 512 1513 MB-1,024 MB 1,024 (1 KB) 21,025 MB-2 GB 2,048 (2 KB) 42 GB-2 TB* 4.096 (4 KB) 8*A terabyte is 1,099,511,627,776 bytes or 1,024 gigabytes and is abbreviated as TB


CTEC 110 26

Clusters and NTFS

Structure of an NTFS Volume


CTEC 110 27

Master File Table (MFT)


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


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


CTEC 110 30

Deciding on a File System


Deciding on a File System

Formatting:

Floppy disk – always FAT file system

Hard disk – you decideCan convert FAT to FAT32/NTFSCannot convert FAT32/NTFS to FAT


disk structures. ctec 1102 formatting a disk two parts to formatting a disk: low-level (physical)...

Documents

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type of disk

retrieved disk structures

disk data sectors

slides slide

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