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Chapter 5, Continued

Chapter 5, Continued. Introduction to Hard Drives. Managing and Maintaining Your PC. Chapter 5B - Introduction to Hard Drives. MENU. Formatting & Optimizing. Disk Compression. Disk Caching. Chapter summary. Formatting. Hard drives are formatted twice

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Chapter 5, Continued

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  1. Chapter 5, Continued Introduction to Hard Drives Managing and Maintaining Your PC

  2. Chapter 5B - Introduction to Hard Drives MENU Formatting & Optimizing Disk Compression Disk Caching Chapter summary

  3. Formatting • Hard drives are formatted twice • Low-level format - physically formats the hard drive and creates tracks and sectors • Today, this is often done at the factory • OS Format - puts the boot record, FAT, and root directory on the disk • Example: FORMAT C:/S • If the hard drive is partitioned, each partition has its own boot record, 2 copies of its FAT, and a root directory

  4. Fragmentation • A fragmented file is one that is in noncontiguous clusters on the disk • As files are deleted, they release space • New files are stored in the available locations and may have to be divided over several locations, thus becoming fragmented • The clusters that comprise a file are called a chain

  5. Fragmentation • Fragmentation is undesirable because • When DOS has to access many different locations on the drive to read a file, access time slows down • If a file becomes corrupted, recovering a fragmented file is more complicated than recovering one in a contiguous chain

  6. Fragmentation • Windows 95 offers a Defragmenter utility • Click Start • Choose Programs • Then Accessories • Then SystemTools • Click DiskDefragmenter • Follow the instructions • Click Yes when done

  7. Windows 95 - Defragment Figure 5-22 Windows 95 disk utilities

  8. Windows 95 - Defragment Figure 5-23 Defragmenter’s status box

  9. Windows 95 - Defragment Figure 5-24 Disk Defragmenter results

  10. Cross-Linked and Lost Clusters • Cross-linked clusters • More than one file points to them • Lost Clusters • No file in the FAT or VFAT points to them • ScanDisk in DOS and Windows 95 can repair these clusters • Run SCANDISK from the DOS prompt or from Windows 95 System Tools

  11. Cross-Linked and Lost Clusters Figure 5-25 Lost and cross-linked clusters

  12. Cross-Linked and Lost Clusters Figure 5-26 SCANDISK for DOS

  13. Cross-Linked and Lost Clusters • From Windows 95 • Click Start • Click Programs • Select Accessories • Then System Tools • Then ScanDisk • ScanDisk asks which drive you want to scan, then performs the scan • ScanDisk reports the errors it finds

  14. Cross-Linked and Lost Clusters Figure 5-27 ScanDisk reports errors

  15. Cross-Linked and Lost Clusters Figure 5-28 ScanDisk results

  16. Disk Compression • A compressed drive is actually a file • The drive contains a non-compressed host drive • Usually a very small partition on the drive, generally under 2MB • Within the host drive is a compressed volume file (CVF) that holds everything on the drive, compressed into 1 file • Drive compression can make a system run slower

  17. Disk Compression Figure 5-29 A compressed drive

  18. Disk Compression • In DOS and Windows 3.x • In the first method, a device driver in the CONFIG.SYS file stores data on the hard drive • The driver treats all the space as one big file called the host file • It takes files from DOS and writes them to the disk, keeping track of the location • The second method compresses one or more files into one small file for easy exporting to other systems

  19. Disk Compression • Windows 95 offers its own disk compressor, called DriveSpace • Assigns a different drive letter to the hard drive • Compresses the entire contents of the drive into a single file • Sets up the drive so Windows 95 and other applications view the file as drive C • Configures Windows 95 so that when it boots it loads and manages the file

  20. Disk Compression • To use DriveSpace in Windows 95 • Click Start • Click Programs • Then Accessories • Then SystemTools • Then click DriveSpace • Select the drive • Click Options • Click OK and the compression begins

  21. Disk Compression Figure 5-30 Selecting drive using DriveSpace for Windows 95

  22. Disk Compression Figure 5-31 Drive compression predictions

  23. Disk Compression Figure 5-32 Drive compression options

  24. Disk Compression Figure 5-33 Drive compression in progress

  25. Disk Compression • After the drive is compressed, there will be 2 logical drives on the disk • The host drive H, which contains the CVF • Contains a Readthis.txt file that explains how to mount a compressed drive • The compressed drive • To get the most resources out of compression, begin with a relatively free hard drive

  26. Disk Compression Figure 5-34 After compression, a 3 1/2-inch disk is now two logical drives A and H

  27. Disk Compression Figure 5-35 Readthis.txt file on host drive

  28. Disk Compression Figure 5-36 An empty 3 1/2-inch disk yields more space than a partially filled disk

  29. Disk Caching • A disk cache is a temporary storage area in RAM for data being read from or written to a hard drive • Hardware cache - contained in RAM chips built right on the disk controller card • Software cache - stored on the hard drive and loaded into memory as a terminate-and-stay-resident (TSR) program

  30. Disk Caching Figure 5-37 A CPU asking a hard drive for data without cache (upper part) and with cache (lower part)

  31. Disk Caching • SMARTDrive is the software that manages the hard drive cache for DOS and Windows 3.x • DOS used to use buffers to speed up disk access, but disk caches are more effective • Many software packages still require that DOS maintain buffers

  32. Disk Caching • Windows 95 has a built-in 32-bit software cache called VCACHE • VCACHE is automatically loaded by Windows without entries in CONFIG.SYS or AUTOEXEC.BAT • VCACHE does not take up conventional or upper memory space • VCACHE allocates the amount of memory it uses based on available memory and disk activity

  33. Using DOS under Windows 95 to Manage a Hard Drive • Some DOS commands that use Windows 95 as the OS may damage a hard drive’s file structure • Some software and commands to avoid • Disk utility software that does not know about VFAT, including older versions of Norton Utilities and Central Points PC Tools • FDISK, FORMAT C:, SYS C:, or CHKDSK while in a DOS session within Windows 95

  34. Using DOS under Windows 95 to Manage a Hard Drive • Other software and commands to avoid • Software to optimize or defragment your hard drive that does not know about long filenames • Hard drive cache programs, unless they are written for Windows 95 • Older DOS backup programs such as BACKUP or MSBACKUP because the long filename information might not be saved during the backup

  35. Chapter Summary • Hard drive capacity is determined by the number of heads, tracks, and sectors on the disk • System BIOS and software can use CHS, large mode, or LBA mode to manage a hard drive • Some older systemboard BIOS may need to be upgraded to support large-capacity drives

  36. Chapter Summary • The FAT lists all clusters on the hard drive and how each is allocated • The root or main directory is created when the drive is first formatted • Ways to optimize drive space and access speed are defragmentation, disk compression, and disk caching • Most PCs today use IDE technology

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