Introduction to Hard Drives

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Chapter 5

• Introduction to Hard Drives

Managing and Maintaining Your PC
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Chapter 5A - Introduction to Hard Drives
MENU
Disk Organization
FAT, DEBUG, VFAT, root dir
Using DOS to manage drives
Using Windows 3.X to manage drives
Using Windows 95 to manage drives
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Hard Drives - Physical Organization

• Modern hard drives have two or more platters, or
  disks, that are stacked together and spin in
  unison
• Read/write heads are controlled by an actuator
  and move in unison across the disks surfaces as
  the disks rotate on a spindle
• Data is stored in tracks and sectors

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Hard Drives - Physical Organization
Figure 5-1 Inside a hard drive case
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Hard Drives - Physical Organization

• Each side of a platter is called a head
• Each head is divided into tracks (or cylinders)
  and subdivided into sectors
• The entire first cylinder is filled before the
  read/write heads move inward to the next cylinder

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Hard Drives - Physical Organization
Figure 5-2 A hard drive with four platters
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Hard Drives - Logical Organization

• To the OS, data is stored in a long list of
  clusters that are organized into files
• The OS uses 2 tables to keep track of which
  clusters are being used for a file along with
  other file information such as filename, file
  length, and whether the file is read-only or a
  hidden file
• The physical location of the file is tracked by
  the BIOS or device driver

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Hard Drives - Logical Organization
Figure 5-3 How the operating system views
the hard drive when managing a file
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Hard Drives - Partitions

• The OS can partition the single physical hard
  drive into more than one logical drive, or
  partition
• A logical drive is a portion of a hard drive that
  an OS views as and manages as an individual drive
• Information about the logical divisions is stored
  in the partition table at the beginning of the
  drive

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Hard Drives - Partitions

• When the drive is partitioned, the OS assigns a
  drive letter to the first partition, usually C
• FDISK first creates a partition, then assigns
  drive letters to each logical drive and creates a
  boot record, FAT, and root directory for each
  logical drive

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Hard Drives - Partitions
Figure 5-4 A single physical drive can be viewed
by the operating system as one or more logical
drives
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Drive Capacity

• The number of sectors present on the drive
  determines the drive capacity
• All sectors in a track hold 512 bytes
• Most earlier drives had 17 sectors per track
• Most drives today have more than 26 sectors per
  track
• tracks sectors/track 512 capacity

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Translation

• Translation converts the addressing of sectors
  when the hard drive addressing system does not
  conform to what System BIOS expects
• Translation is required
• When a drive uses zone bit recording
• Does not use the same number of sectors per track
  throughout the drive
• On large-capacity drives

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Zone Bit Recording
Figure 5-5 Floppy drives and older hard drives
use a constant number of sectors per track
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Zone Bit Recording
Figure 5-6 Zone bit recording can have more
sectors per track as the tracks get larger
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Large-Capacity Drives

• Drives that exceed 1,024 cylinders and more than
  528MB are large capacity and require an
  Enhanced BIOS
• BIOS supports a hard drive as
• CHS (Cylinders, Heads, Sectors) or normal mode
• Large mode (504MB to 1G), translation
• LBA (Logical Block Addressing) mode

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CHS or Normal Mode

• Cylinders, heads, sectors (CHS) mode is the
  traditional method used by BIOS to read from and
  write to hard drives by addressing the correct
  cylinder, head, and sector
• Requires no translation
• Limited to 1,024 cylinders, 16 heads, and 63
  sectors per track
• Maximum drive capacity of 504MB

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Large Mode

• Large mode supports drives with a capacity from
  504MB to 1 GB
• A translation method
• The location of the data on the drive is remapped
  to conform to the 504MB barrier
• Then the address information is passed to the OS
• A CMOS setting for this mode often reads either
  large mode or translation

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Enhanced BIOS or LBA Mode

• Logical block addressing (LBA) is a translation
  method similar to the FAT
• It sends an LBA number to the OS, which is
  correlated with a particular cylinder, head, and
  sector number
• LBA 0 stands for cylinder 0, Head 0, and sector 1
• The OS views the drive as a long list of LBAs

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When BIOS Does Not Support Large-Capacity Drives

• If you want to install a large-capacity drive on
  a PC whose BIOS does not support it, you can
• Upgrade the BIOS
• Upgrade the entire system
• Use software that interfaces between the old BIOS
  and the new drive
• Some drives come with disk manager software
  already installed

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File Allocation Table

• The OS manages files on the hard drive using the
  FAT and a 2nd FAT copy
• FAT contains one entry for each cluster
• A file is stored in one or more clusters
• How to determine the size of a cluster
• Use the CHKDSK command
• Use DIR to see how much disk space is available,
  create and save a one-character file, use DIR
  again to see the difference

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File Allocation Table
Figure 5-7 FAT showing two files
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DEBUG Utility

• DEBUG is a utility in DOS and Windows 95 that
  displays the hexadecimal values of the FAT and
  other areas of the hard drive
• It is an editor
• It can look at any sector on the hard drive or
  disk
• It is a valuable aid for recovering data on a
  damaged disk or hard drive

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DEBUG Utility
Table 5-1 Notepad and DEBUG are both Editors
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DEBUG Utility

• These DEBUG instructions created the memory dump
  on the next slide
• C\gtDEBUG Execute DOS DEBUG
• -L90000 2 1 1 Load into memory addresses
  beginning with 9000 from drive 2 (drive
  C), starting with sector 1
• and reading 1 sector
• -D90000 Dump or Display the contents of
  memory starting at 9000

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DEBUG Utility
Figure 5-8 Beginning of a FAT on a hard drive
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DEBUG Utility
Figure 5-9 Second copy of FAT
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Virtual File Allocation Table

• The VFAT helps Windows 95 accommodate long
  filenames
• The filename and extension are stored in the root
  directory or a subdirectory list
• Each entry is 32 bytes long, called a block
• Long filenames require more than one block in the
  directory
• When the OS allocates blocks for long names, it
  stores the information in the VFAT

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Virtual File Allocation Table

• The VFAT records how many blocks are allocated to
  each file listed in the directory
• It is a variation of the DOS 16-byte FAT
• It is a virtualized 32-bit FAT that is, it is
  not a real 32-bit FAT
• Some DOS-based utility programs can damage the
  VFAT entries
• The DEL command can leave the extra blocks for
  long filenames unavailable for later use
• SCANDISK can recover these blocks, however

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Root Directory

• The layout of the root directories for hard
  drives is the same as that for floppy disks
• Total number of bytes for each file is 32
• Date and time are stored as integers
• The OS creates the root directory when it formats
  the drive
• Has a fixed number of entries
• Immediately follows 2nd copy of the FAT

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Root Directory
Table 5-2 Root Directory Information for each
File
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Root Directory
Table 5-3 File Attributes as Listed in the
Directory Attribute Byte (Reading from left to
right across the byte)
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Root Directory
Figure 5-10 A root directory
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Root Directory
Table 5-4 Example of FAT Entries for First Two
Files in Root Directory
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Using DOS to Manage Hard Drives - Subdirectories

• MKDIR (MD) command - creates a subdirectory
  within a directory
• MD C\GAME creates a parent directory named GAME
  on drive C
• MD C\GAME\CHESS creates a subdirectory named
  CHESS under the \GAME directory

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Using DOS to Manage Hard Drives - Subdirectories
Figure 5-11 DIR of the \GAME directory
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Using DOS to Manage Hard Drives - Subdirectories
Figure 5-12 Dump of subdirectory table C\GAME
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Using DOS to Manage Hard Drives - CHDIR

• CHDIR (CD) command - changes the current default
  directory
• CD C\GAME\CHESS Moves you into the CHESS
  subdirectory of \GAME
• C\GAME\CHESSgt CD.. Moves you from the child
  directory CHESS to its parent directory GAME

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Using DOS to Manage Hard Drives - RMDIR

• RMDIR (RD) command - removes the named directory
• The directory must not contain any files or
  subdirectories
• The directory must not be the current directory
• RD C\GAME\CHESS Removes the CHESS subdirectory
  of \GAME

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Using DOS to Manage Hard Drives - DELTREE TREE

• DELTREE command - deletes a directory and all its
  subdirectories
• DELTREE C\GAME deletes the directory GAME and
  any subdirectories it contains
• TREE command - displays the directory structure
  of a hard drive or disk
• /A option specifies test
• /F option includes filenames in the list

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Using DOS to Manage Hard Drives - ATTRIB

• ATTRIB command - Displays or changes the
  read-only, archive, system and hidden attributes
  assigned to files
• ATTRIB H filename Hides a file
• ATTRIB -H filename Unhides a file
• R and -R options change the read-only status (R
  prevents changes or deletes)
• A and -A options turn the archive bit on and
  off, respectively

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Using DOS to Manage Hard Drives - MIRROR

• MIRROR command - Saves partition table
  information to a disk
• MIRROR /PARTN
• UNFORMAT command - Reverses the effect of an
  accidental format and repairs any damage to a
  partition table that has been previously saved
  with the MIRROR command
• UNFORMAT C and UNFORMAT /PARTN

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Using DOS to Manage Hard Drives - Batch Files

• If you have a list of DOS commands that you will
  want to execute several times, you can save the
  list of commands in a batch file with the
  extension .BAT
• Example of a short .BAT file
• C
• CD\UTILITY\TOOLS
• COPY . A

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Using Windows 3.x to Manage Hard Drives

• Windows 3.x File Manager performs most of the
  hard drive management tasks
• When you first enter File Manager, you will
  probably see only the directories under the root
  directory
• To see their subdirectories, click or
  double-click the directory name
• From File Manager, Click File menu to see a list
  of file management functions

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Using Windows 3.x to Manage Hard Drives
Figure 5-13 File menu in File Manager of Windows
3.1
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Using Windows 3.x to Manage Hard Drives

• To create a new directory from File Manager
• Click File menu
• Click Create Directory
• Enter the name of the directory, following the
  same rules as for creating a directory in DOS
• Click OK

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Using Windows 3.x to Manage Hard Drives
Figure 5-14 Creating a directory in Windows 3.1
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Using Windows 3.x to Manage Hard Drives
Figure 5-15 A new directory called chess is
created under \GAMES
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Using Windows 3.x to Manage Hard Drives

• To delete a directory from File Manager
• Click the name of the directory
• Press the delete key
• If the correct directory has been selected for
  deletion, click OK

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Using Windows 3.x to Manage Hard Drives
Figure 5-16 Deleting a directory
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Using Windows 3.x to Manage Hard Drives

• File Properties in File Manager is similar to the
  DOS ATTRIB command
• To display the properties of a file
• Click the name of the file
• Go to File menu and select Properties
• The Properties box appears
• You may make changes to the attributes
• Click OK to save any changes or Cancel to exit
  without making changes

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Using Windows 3.x to Manage Hard Drives
Figure 5-17 The properties of a file
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Using Windows 95 to Manage Hard Drives

• Windows 95 Explorer is the primary tool for
  managing files on the hard drive
• To open Explorer
• Click Start
• Click Programs
• Click Windows Explorer, or
• Right-click My Computer
• Select Explorer

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Using Windows 95 to Manage Hard Drives

• To create a new folder in Explorer
• Click the name of the folder within which the new
  folder will go
• Click the File menu
• Select New
• Select Folder a folder will be created with the
  name New Folder
• Click the folder name and change its name

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Using Windows 95 to Manage Hard Drives
Figure 5-18 Create a new folder
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Using Windows 95 to Manage Hard Drives
Figure 5-19 Edit the new folders name
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Using Windows 95 to Manage Hard Drives

• To delete a folder from Explorer
• Right-click the folder
• Select Delete from the menu
• A confirmation box will appear
• If you have selected the correct folder for
  deletion, respond Yes
• The folder and its contents will be placed in the
  Recycle Bin
• The disk space has been freed

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Using Windows 95 to Manage Hard Drives
Figure 5-20 Delete a folder in Windows 95
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Using Windows 95 to Manage Hard Drives

• To view and change file attributes from Explorer
• Right-click a file
• Select Properties from the menu
• The Properties box appears
• You may make changes to the attributes
• Click OK to save any changes or Cancel to exit
  without making changes

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Using Windows 95 to Manage Hard Drives
Figure 5-21 Properties of a file in Windows 95
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Managing Hard Drives

• The PATH command works the same in DOS, Windows
  3.x, and Windows 95
• If you have an AUTOEXEC.BAT in your root
  directory, Windows 95 reads the PATH command in
  that file
• If you do not have an AUTOEXEC.BAT file, Windows
  95 uses the path
• C\WindowsC\Windows\Command