CSC 2260 Operating Systems and Networks
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Transcript of CSC 2260 Operating Systems and Networks
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CSC 2260Operating Systems and Networks
Chapter 2
Fall 2008
Dr. Chuck Lillie
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Disk Operating System (DOS)
Finding DOS and Understanding its Strengths and WeaknessesInstalling DOSHow the FAT File System WorksWorking with the DOS Command PromptUnderstanding the DOS Bootup ProcessTroubleshooting Common DOS Problems
Chapter
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Learning Objectives
Measure the value, strengths, and weaknesses of DOS
Install DOS Use the FAT file system Use DOS commands for file management and
other tasks Describe the DOS bootup process and create
startup disks Troubleshoot common DOS problems
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Finding DOS and Understanding its Strengths and Weaknesses
Versions of DOSCP/M was an important predecessor to
DOSMany versions of DOS, several introduced
by Microsoft (MS)MS created PC DOS for IBMLater licensed DOS as MS-DOS to other
manufacturersMS-DOS 5.0 first version available as a
separate product
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Finding DOS and Understanding its Strengths and Weaknesses
Versions of DOS (continued) PC DOS now works on Microsoft/Intel
compatible computersDigital Research (of CP/M fame) introduced
DR-DOS in 1987DR-DOS 8.0 introduced in 2004 by
DeviceLogicsFreeDOS distributed without charge under
GNU GPL license
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Finding DOS and Understanding its Strengths and WeaknessesDOS’ Strengths
DOS for backward compatibility with DOS appsDOS when you need a small OSDOS is more compact than Windows and
hence useful for embedded systems or for portability
DOS is popular as an operating system due to its ability to pack all startup files on a single floppy disk
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Finding DOS and Understanding its Strengths and Weaknesses
DOS Strengths (continued)The floppy disk is also known as the startup
diskStartup disk accommodates additional files,
such as drivers and utilitiesStartup disk can be used for booting up a
computer and running special diagnostic programs
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Finding DOS and Understanding its Strengths and Weaknesses
DOS Weaknesses Processor mode limitsMemory limitsMultitasking limitsHard drive limits
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Finding DOS and Understanding its Strengths and WeaknessesDOS Weaknesses (continued)
Processor Mode Limits Only supports real mode of operation of Intel
processors Newer Intel processors start in the real mode, and
newer OSs (Windows, Linux, UNIX) switch the processor from the real mode to the protected mode
Memory Limits Intel processors in real mode use only 1 MB640 KB of RAM (conventional memory) is workspace
for the OS, applications and data384 KB of addresses reserved for system BIOS and
RAM and ROM on adapters
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Finding DOS and Understanding its Strengths and Weaknesses
DOS Weaknesses (continued) Multitasking Limits
DOS is a single-tasking OSHard Drive Limits
DOS only supports hard drives up to 7.8 GBDOS uses logical drives that are 2 GB or less
and within the 7.8 GB total disk space limit
A logical drive is a portion of the physical hard drive with a letter assigned to it
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Installing DOS
DOS Hardware Requirements The general DOS hardware requirements
for MS-DOS 6.22 and IBM PC-DOS
An IBM or compatible personal computer6MB of free hard disk space for the DOS utilities512KB of memory
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Installing DOS
Preparing for DOS InstallationAssure that the computer is a complete
system with all the necessary components
Setup program partitions and formats the hard disk
Partition: an area of a physical hard disk that contains one or more logical drives
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Installing DOSPartitioning a Hard Disk in MS-DOS
Physical format is done at the factory Master Boot Record (MBR), the 1st sector
on disk, contains the partition tablePartitioning is the first step to prepare a
hard diskEach partition needs a logical format within
each logical drivePartitioning and formatting included in OS
installation
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Installing DOS
Partitioning a Hard Disk in MS-DOS (continued)FDISK – the partitioning program of MS-DOSPrimary partition has only one logical drive2GB is maximum primary partition size in
MS-DOSExtended partition contains one or more
logical drivesAfter partitioning, then format logical drives
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Installing DOS
Step-by-Step 2.01
Installing DOS on a Hard Disk
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How the FAT File System Works
FAT File System ComponentsFAT Table
File allocation table (FAT) – DOS records disk space usage
Cluster – minimum space allocated to a file
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How the FAT File System Works
FAT File System Components (continued)FAT12, FAT16, and FAT32
FAT16 – used on hard disksFAT32 – available since Windows 95 OEM SR2FAT12 – used on floppy disks
The number refers to the size of each entry in the FAT table. Length of entry limits the number of entries the FAT table can hold.
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How the FAT File System Works
FAT File System Components (continued)How Cluster Size Affects Partitions
FAT16 file system limited to 65,525 clustersMaximum cluster size 32,768 bytes (32K)65,525 x 32,768 = 2GB (maximum partition size
supported by the FAT16 file system)
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How the FAT File System Works
FAT File System Components (continued)Root Directory and Other Directories
The FAT and the root directory are the two primary components of the FAT file system
DOS uses the FAT to record the location of a file on the disk
A directory is a place where DOS stores information about files, including a referenceto the FAT table
Root directory is the top level directory
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How the FAT File System Works
FAT File System Components (continued)Root Directory and Other Directories
(continued)Parent directory contains other directoriesChild directory (subdirectory) is within a parentEach directory entry contains the name of a file
or directory, the time and date of its creation or modification, its size, attributes, and beginning cluster information
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How the FAT File System Works
Using a Directory and the FAT Table to find a FileDirectory is like a phone directory for DOSFinds file name and listing in the directoryReads the starting cluster number in
directoryLooks in the FAT table (like a map of city)
for location on disk
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How the FAT File System Works
DOS file-naming rules: A file name is up to eight characters, followed
by a period, and an extension of up to three characters
A file name and extension can include alpha-numeric characters and a few special characters, but no spaces
Use the wildcard characters asterisk (*) and question mark (?) to locate files and folders
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How the FAT File System Works
DOS File TypesBAK, BAS, BAT, COM, DOS, EXE, SYS,
and TXT are some common file extensions and file types recognized by DOS
Executable Files COM, EXE, and BAT are the three types of
files that can be executed by DOS
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How the FAT File System Works
Step-by-Step 2.02
Creating a Simple Batch File
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How the FAT File System Works
Read-only
Archive System
Hidden Volume
label Directory
•DOS File Attributes
•Determine the manner in which DOS handles files
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How the FAT File System Works
LABEL commandCreates or changes a volume label (name) If a volume has a label, FORMAT requires
the name before reformatting
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How the FAT File System Works
ATTRIB commandDisplays and modifies attributes Works on read-only, archive, system, and
hidden filesWorks in both MS-DOS and Windows on
FAT and NTFS
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Working with the DOS Command Prompt
Success at the DOS PromptSuccess means correctly entering
commands and getting desired results
Important for working with DOS and other OSs
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Working with the DOS Command Prompt
Step-by-Step 2.03
Using the Online Help in DOS
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Working with the DOS Command Prompt
Success at the DOS Prompt (continued)What is the Correct Syntax?
Syntax is a set of rules for correctly entering a specific command at the command line
The HELP command can be used to find the syntax for a command
COMMAND /?
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Working with the DOS Command Prompt
Success at the DOS Prompt (continued)How is a Command Interpreted?
COMMAND.COM interprets the command entered at the prompt
COMMAND.COM loads each command into the memory, and issues additional instructions to the command
COMMAND.COM parses the command entry based on special delimiter characters
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Working with the DOS Command Prompt
How is a Program Found and Loaded?COMMAND.COM loads the command
named at the beginning of the command line
Must find the actual program codeFirst checks its own list of internal commands Then looks for an external command in the
current directory, and then in a list called the search path
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Working with the DOS Command Prompt
Learning to Manage Files and DirectoriesFile management in DOS is centered on the
abilities and limits of the FAT file system It is essential to design a directory structure
to save and organize files
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Working with the DOS Command Prompt
Learning to Manage Files and Directories (continued)Designing a Directory Structure for File
ManagementDOS directory/folder structure is hierarchicalDrive | Directory | File NameTREE command can be used to view the entire
directory structureStore data in a separate directory from applications
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Working with the DOS Command Prompt
Learning to Manage Files and Directories (continued)Creating and Removing Directories
MD (Make Directory) will create a directoryCD or CHDIR (Change Directory) allows
movement between directoriesRD (Remove Directory) deletes an empty
directory
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Working with the DOS Command Prompt
Learning to Manage Files and Directories (continued)Use File Management Commands
DOS commands are divided into internal commands and external commands
Internal commands are loaded into the memory along with DOS
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Working with the DOS Command Prompt
Learning to Manage Files and Directories (continued)Use File management commands
(continued):DIR (Directory), MD, CD, CLS (CLear Screen),
COPY, REN (REName), RD, and TYPE are some of the internal commands
XCOPY, DISKCOPY, and DELTREE are often-used external commands
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Working with the DOS Command Prompt
DOS Command Function
DIR Displays a list of files and folders.
DIR /? Lists the available syntax for the DIR command.
DIR /P List data one page at a time.
CD .. Moves to the parent directory from the present directory.
CLS Clears the screen.
VER Displays the MS-DOS version.
XCOPY Used to copy files and entire directories.
COPY Used to copy only files.
DELTREE Used to delete an entire directory and its contents.
DOS commands and their
functionality
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Working with the DOS Command Prompt
Step-by-Step 2.04
Managing Files and Directories
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Understanding the DOS Boot-Up Process and Startup Disks
Why You Should Learn the DOS Bootup ProcessPersonal computers are multi-purpose
devices.Understanding the normal startup process
of the system helps troubleshoot problems that
occur during boot-up.
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Understanding the DOS Boot-Up Process and Startup Disks
DOS system files IO.SYS handles hardware interaction and
loading of drivers
MSDOS.SYS is the kernel of DOSCOMMAND.COM is the command interpreter
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Understanding the DOS Boot-Up Process and Startup Disks
DOS system files (continued)DOS Configuration FilesCONFIG.SYS – adds device drivers and
modifies DOS settings
BUFFERS DOS
DEVICE FILES
DEVICEHIGH STACKS
AUTOEXEC.BAT batch file loaded during bootup
PATH PROMPT SET
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Understanding the DOS Boot-Up Process and Startup Disks
The DOS Bootup ProcessA PC can be booted up by:
Turning on the power switch of the PC (a cold boot)
Using the Ctrl-Alt-Delete key combination to reboot the system (a warm boot)
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Understanding the DOS Boot-Up Process and Startup DisksThe DOS Bootup Process (continued)
The processor loads a special ROM-based program, called Power-On Self-Test (POST)
POST runs a series of small diagnostic tests
on the hardware, and loads the bootstrap loader
The bootstrap loader is a small program in the ROM BIOS
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Understanding the DOS Boot-Up Process and Startup Disks
The DOS Bootup Process (continued)On a hard drive, the bootstrap loader looks into
the MBR (master boot record) and reads the partition table for the primary active partition
The bootstrap loader loads the boot sector from the logical drive, which, in turn, runs the operating system loading program
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Understanding the DOS Boot-Up Process and Startup Disks
Creating a DOS Startup Floppy DiskUsing FORMAT to create a startup diskUsing SYS to create a startup diskUsing Windows to create a startup disk
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Understanding the DOS Boot-Up Process and Startup Disks
Using FORMAT to Create a Startup DiskThe FORMAT command prepares the
diskette and places a new root directory and FAT on the disk
The /S switch option places the system files on the diskette
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Understanding the DOS Boot-Up Process and Startup Disks
Step-by-Step 2.05
Create a Startup Floppy Disk Using FORMAT
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Understanding the DOS Boot-Up Process and Startup Disks
Using SYS to Create a Startup DiskThe SYS command places the DOS system
files on a previously formatted floppy disk
To put the DOS system files on a floppy disk enter sys a:
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Understanding the DOS Boot-Up Process and Startup Disks
Using Windows to Create a Startup Disk In Windows 95 and 98 go to Control Panel |
Add/Remove Programs | Startup Disk In Windows XP format a disk from within My
Computer or Windows Explorer and select the option to create a MS-DOS startup disk
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Troubleshooting Common DOS Problems
“Non-System Disk” error messageThe OS loader program (boot sector) is
unable to locate the IO.SYS, or MSDOS.SYS, or both
Rectify by ensuring that the OS is booted from the disk that holds the OS
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“Bad or Missing Command Interpreter”error message Implies that the file COMMAND.COM is
missing or that the version is different than IO.SYS and MSDOS.SYS
Rectify by copying the COMMAND.COM file with the correct date and time from the floppy disk to the hard disk
Troubleshooting Common DOS Problems
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“Bad Command or File Name” error message Implies that the command name or the file
name (or a directory name) used in the command line is incorrect
Rectify by identifying typos and re-entering the command correctly
Troubleshooting Common DOS Problems
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Troubleshooting Common DOS Problems
A request to enter the current date and timeMeans that DOS did not find an
AUTOEXEC.BAT file
If you previously had one, investigate why and how you don’t now
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Chapter Summary
Finding DOS and Understanding Its Strengths and Weaknesses One reason DOS is still in limited use today is its
small size, which makes it a choice for embedded systems
Another reason is that its system files easily fit on a floppy disk, leaving room for other small programs
Technicians can run diagnostic utilities from a DOS floppy disk
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Chapter Summary
Finding DOS and Understanding Its Strengths and Weaknesses Windows can run DOS in a virtual DOS machine Some applications run too slowly or not at all
in a virtual machine, so they must be run on a computer running DOS
DOS can only access real-mode of the Intel processors
DOS is a single-tasking operating system DOS provides limited services for DOS
applications
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Chapter Summary
Finding DOS and Understanding Its Strengths and Weaknesses DOS applications can only use conventional
memory Microsoft no longer supports or sells MS-DOS IBM sells PC DOS 2000 Digital Research sold DR-DOS to Novell DR-DOS is now sold through DeviceLogics Versions of DOS can be found for free on the
Internet
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Chapter Summary
Installing DOSThe MS-DOS Setup program will partition
and format a hard drive, if neededHardware requirements for MS-DOS are
minimal:An IBM or compatible PC6MB of free hard disk space512KB of memory
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Chapter Summary
How the FAT File System Works DOS uses the FAT16 file system, and only uses
conventional memory The FAT file system uses the 8.3 naming
convention for files and directories It is best to use only alphanumeric characters A file’s extension can indicate the type of file File attributes determine how DOS handles a file
or directory File attributes are read-only, archive, system,
hidden, volume label, and directory
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Chapter Summary
Working with the DOS Command Prompt The ATTRIB command allows you to view
and manipulate the read-only, archive, system, and hidden attributes
Internal command are part of COMMAND.COM and are always available and fast to access
CLS, COPY, REN, DEL, MD, RD, CD, and TYPE are internal DOS commands
External commands are in individual files, which must be where DOS can find them
XCOPY, DELTREE, FORMAT, FDISK, and DISKCOPY are external commands
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Chapter Summary
Describe the DOS Bootup Process and Create Startup Disks It is important to understand the bootup
process of an OS in order to troubleshoot failures that occur during bootup
A hard boot of a PC occurs when you turn on the power switch
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Chapter Summary
Describe the DOS Bootup Process and Create Startup DisksA soft boot of a PC occurs when you press
CTRL-ALT-DELETEMany computers have a Reset button,
which resets a running computer without a power-down and power-up cycle
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Chapter Summary
Describe the DOS Bootup Process and Create Startup Disks The order of events during bootup of DOS is:
Cold or warm boot POST Bootstrap loader looks on A: or C: drive and
loads the boot record IO.SYS and MSDOS.SYS are loaded CONFIG.SYS (if it exists) is read and used by MSDOS.SYS COMMAND.COM is loaded
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Chapter Summary
Describe the DOS Bootup Process and Create Startup Disks DOS bootup order of events (continued)
AUTOEXEC.BAT (if it exists) is read and used by COMMAND.COM
The DOS prompt is displayed
To create a DOS startup disk, you can: Use the DOS Setup program Use the SYS or FORMAT command Use the Startup Disk option in Windows 9x Format a floppy disk in Windows XP
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Chapter Summary
Troubleshoot Common DOS Problems A “Non-System Disk” error message means that
the OS loader cannot find IO.SYS or MSDOS.SYS Most likely cause is a data floppy disk left in drive A: Remove the floppy and reboot the computer A “Bad or Missing Command Interpreter” message
means that COMMAND.COM is missing or is a different version than IO.SYS and MSDOS.SYS
Boot from a DOS floppy disk of the correct version, and copy COMMAND.COM to the root of C:
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Chapter Summary
Troubleshoot Common DOS Problems A “Bad Command or File Name” error message
means you need to check your spelling and reenter the command
If you are required to enter the date and time when you boot up a computer there is probably no AUTOEXEC.BAT on the root of the boot disk. Create one, even if it is empty, and most PCs will use the internal clock for the time