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Chapter 6

Chapter 6. Disk Operating System. Hardware. ROM BIOS. Operating System. Internal Commands External Commands. Memory I/O Device’s. Applications. Video Area. 640 K. Program Memory. Command Resident. MS-DOS. IO System. Interrupt Handler. 0000.

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Chapter 6

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  1. Chapter 6 Disk Operating System

  2. Hardware ROM BIOS Operating System Internal Commands External Commands Memory I/O Device’s Applications

  3. Video Area 640 K Program Memory Command Resident MS-DOS IO System Interrupt Handler 0000 Figure 2 Memory Map of 8088 Processor

  4. Flat File System

  5. Flat Issues

  6. Hierarchical File System

  7. C:DOS (ROOT dir) Chicago dir Atlanta dir Portland dir Payroll Inventory Payroll Inventory Payroll Inventory Files Files Files Files Files Files

  8. Path statement • Absolute pathname • C:\US\sales\salesreps\smith • Relative pathname • CD \smith • “Program not found”

  9. 8.3 File Specification A:\DIRNAME\FILENAME.EXT Drive location Directory location File Name Can be up to 8 eight characters The following characters are not allowed: . ” / \ [ ] < > + = ; ‘ Spacebar Extension

  10. Commands • Name Options Parameters • Keyword Drive Options • Keyword Source file File switches • Do what? To who? How?

  11. Command Essentials • You must enter words shown in capital letters y). • You must supply any items shown in italic letters • Items in square brackets [] are optional. • Items separated by a bar ( | ) means you can enter one of the other ( Example OFF | ON ) • An Ellipsis (…) indicates you can repeat as many time as you want. • You must include all punctuation, except square brackets and vertical bars.

  12. Global Filename Characters • ? = can be any character • * = any character can occupy that position and all remaining positions • DIR A:INPUT.??? Or DIR A:INPUT.* • ******WARNING******* • DELETE C:*.* • ******WARNING*******

  13. Batch Commands • ECHO,FOR,GOTO,IF,PAUSE,REM • A batch file is a file containing 1 or more commands that DOS executes. ext = .bat • ECHO ON • REM This is an example of a batch cmd. • Copy C:prog1.exe to C:prog2.exe • DIR • Autoexec.bat = start program at DOS start

  14. Redirection • DIR >PRN Sends cmd to printer • DIR >catalog Sends cmd to filename • MYPROG <INPUT.TXT • DIR >> filename appends to file

  15. Piping & Filters • Filters = SORT, FIND,MORE • DIR|SORT>FILE • SORT <MYFILE >RESULT • TYPE MYFILE|MORE

  16. Help /? • Command Summary C:>Help • Help command-name (C:>help copy) • Copy /?

  17. C:>copy /?

  18. Physical Structure of a Diskette • Formatting • concentric circles called tracks • pie-shaped wedges called sectors • Data is written to the tracks as bits,0’s and 1’s • bits become magnetized spots on the disk • spacing prevents one spot from affecting other spots • Read/write heads • above and below the diskette move in unison • Diskette made up of Mylar • covered with either cobalt oxide or iron oxide to hold magnetic charge • Formatting writes the division symbol ÷ F6 1111 0110 to each track

  19. Logical Structure of a Diskette • The BIOS manages the disk in sectors, physical terms • a sector holds 512 bytes of data • The OS manages the disk in clusters, logical terms • A cluster is defined as the smallest unit of data that can be read from or written to at one time • File allocation unit (FAT) • One cluster equals the amount of storage space per two sectors, top and bottom of the diskette 512 bytes X 2 = 1024 (one cluster, double-density 3.5” diskette ) 80 X 9 = 720 (one side of diskette in sectors, the whole diskette in terms of clusters) 1024 X 720 = 737,280

  20. Diskette size Tracks per side Number of sectors per tracks Capacity 5.25" Single side SD8 40 8 40 X 8 X 512 bytes = 160 KB 5.25" Double side DD9 40 9 2 X 40 X 9 X 512 bytes = 360 KB 5.25" Double side High Density DQ15 80 15 2 X 80 X 15 X 512 bytes = 1.2 MB 3.5" DD DQ9 80 9 2 X 80 X 9 X 512 bytes = 720 KB 3.5" HD DQ18 80 18 2 X 80 X 18 X 512 bytes = 1.44 MB 3.5" XD ( IBM only) DG36 80 36 2 X 80 X 36 X 512 bytes = 2.88 MB The Standard PC Diskette Configuration: Diskette drives turn at 300 RPM. That results in an average search time (½ revolution) of 100 ms.

  21. IDE/ATA 3 ½ Hard Disk

  22. Tracks, Cylinders, and Sectors

  23. $64 Million Question $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ What does this have to do with security? $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

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