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Chapter 5 Introduction to Hard Drives Managing and Maintaining Your PC 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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Chapter 5 l.jpg
Chapter 5

Introduction to Hard Drives

Managing and Maintaining Your PC


Chapter 5a introduction to hard drives l.jpg
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 EnhancedBIOS

  • 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:\>DEBUG Execute DOS DEBUG

    -L9000:0 2 1 1 Load into memory addresses beginning with 9000 from drive 2 (drive C), starting with sector 1

    and reading 1 sector

    -D9000:0 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\CHESS> 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 WindowsExplorer, or

    • Right-click MyComputer

    • 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 folder’s 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 RecycleBin

    • 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:\Windows;C:\Windows\Command


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