McGraw-Hill/Irwin© 2006 The McGraw-Hill Companies, Inc. All rights reserved. 2-1.

2-1McGraw-Hill/Irwin © 2006 The McGraw-Hill Companies, Inc. All rights reserved.

Disk Operating System (DOS)

Finding DOS and Understanding its Strengths and Weaknesses

Installing DOSHow the FAT File System Works

Working with the DOS Command PromptUnderstanding the DOS Bootup ProcessTroubleshooting Common DOS Problems

Chapter

2


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



•Versions of DOS• CP/M was an important predecessor to DOS• Many versions of DOS, several introduced

by Microsoft (MS)• MS created PC DOS for IBM• Later licensed DOS as MS-DOS to other

manufacturers• MS-DOS 5.0 first version available as a separate

product



•Versions of DOS (continued) • PC DOS now works on Microsoft/Intel

compatible computers• Digital Research (of CP/M fame) introduced

DR-DOS in 1987• DR-DOS 8.0 introduced in 2004 by DeviceLogics• FreeDOS distributed without charge under

GNU GPL license



•DOS’ Strengths• DOS for backward compatibility with DOS apps• DOS when you need a small OS• DOS 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



•DOS Strengths (continued)

• The floppy disk is also known as the startup disk

• Startup disk accommodates additional files, such as drivers and utilities

• Startup disk can be used for booting up a computer and running special diagnostic programs



•DOS Weaknesses • Processor mode limits• Memory limits• Multitasking limits• Hard drive limits



• DOS 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 MB• 640 KB of RAM (conventional memory) is workspace

for the OS, applications and data• 384 KB of addresses reserved for system BIOS and

RAM and ROM on adapters



•DOS Weaknesses (continued)

• Multitasking Limits • DOS is a single-tasking OS

• Hard Drive Limits • DOS only supports hard drives up to 7.8 GB• DOS 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


Installing DOS

•DOS Hardware Requirements • The general DOS hardware requirements for

MS-DOS 6.22 and IBM PC-DOS • An IBM or compatible personal computer• 6MB of free hard disk space for the DOS utilities• 512KB of memory


Installing DOS

•Preparing for DOS Installation• Assure 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


Installing DOS

•Partitioning 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 table• Partitioning is the first step to prepare a

hard disk• Each partition needs a logical format within

each logical drive• Partitioning and formatting included in OS

installation


Installing DOS

•Partitioning a Hard Disk in MS-DOS (continued)

• FDISK – the partitioning program of MS-DOS• Primary partition has only one logical drive• 2GB is maximum primary partition size in

MS-DOS• Extended partition contains one or more

logical drives• After partitioning, then format logical drives


Installing DOS

Step-by-Step 2.01

Installing DOS on a Hard Disk

Page 55


How the FAT File System Works

•FAT File System Components• FAT Table

• File allocation table (FAT) – DOS records disk space usage

• Cluster – minimum space allocated to a file



•FAT File System Components (continued)

• FAT12, FAT16, and FAT32• FAT16 – used on hard disks• FAT32 – available since Windows 95 OEM SR2• FAT12 – used on floppy disksThe 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.




• How Cluster Size Affects Partitions • FAT16 file system limited to 65,525 clusters• Maximum cluster size 32,768 bytes (32K)• 65,525 x 32,768 = 2GB (maximum partition size

supported by the FAT16 file system)




• 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




• Root Directory and Other Directories (continued)

• Parent directory contains other directories• Child directory (subdirectory) is within a parent• Each 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



•Using a Directory and the FAT Table to find a File• Directory is like a phone directory for DOS• Finds file name and listing in the directory• Reads the starting cluster number in directory• Looks in the FAT table (like a map of city) for

location on disk



•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



•DOS File Types• BAK, 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



Step-by-Step 2.02

Creating a Simple Batch File

Page 63



• Read-only• Archive • System

• Hidden• Volume

label• Directory

•DOS File Attributes

•Determine the manner in which DOS handles files



•LABEL command• Creates or changes a volume label (name)• If a volume has a label, FORMAT requires

the name before reformatting



•ATTRIB command• Displays and modifies attributes • Works on read-only, archive, system, and

hidden files• Works in both MS-DOS and Windows on

FAT and NTFS


Working with the DOS Command Prompt

•Success at the DOS Prompt• Success means correctly entering commands

and getting desired results• Important for working with DOS and other OSs



Step-by-Step 2.03

Using the Online Help in DOS

Page 68



•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 /?



•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



•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 code

• First 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



•Learning to Manage Files and Directories• File 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



•Learning to Manage Files and Directories (continued)

• Designing a Directory Structure for File Management• DOS directory/folder structure is hierarchical• Drive | Directory | File Name• TREE command can be used to view the entire

directory structure• Store data in a separate directory from

applications




• Creating and Removing Directories• MD (Make Directory) will create a directory• CD or CHDIR (Change Directory) allows

movement between directories• RD (Remove Directory) deletes an empty

directory




• Use File Management Commands• DOS commands are divided into internal

commands and external commands• Internal commands are loaded into the memory

along with DOS




• 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



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



Step-by-Step 2.04

Managing Files and Directories

Page 73


Understanding the DOS Boot-Up Process and Startup Disks

•Why You Should Learn the DOS Bootup Process• Personal computers are multi-purpose devices.• Understanding the normal startup process of

the system helps troubleshoot problems that occur during boot-up.



•DOS system files• IO.SYS handles hardware interaction and

loading of drivers

• MSDOS.SYS is the kernel of DOS• COMMAND.COM is the command interpreter



•DOS system files (continued)

• DOS Configuration Files• CONFIG.SYS – adds device drivers and modifies

DOS settingsBUFFERS DOSDEVICE FILESDEVICEHIGH STACKS

• AUTOEXEC.BAT batch file loaded during bootupPATH PROMPT SET



•The DOS Bootup Process• A 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)



•The 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



•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



•Creating a DOS Startup Floppy Disk• Using FORMAT to create a startup disk• Using SYS to create a startup disk• Using Windows to create a startup disk



•Using FORMAT to Create a Startup Disk• The 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



Step-by-Step 2.05

Create a Startup Floppy Disk Using FORMAT

Page 83



•Using SYS to Create a Startup Disk• The 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:



•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


Troubleshooting Common DOS

Problems •“Non-System Disk” error message

• The 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


•“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


Problems


•“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


Problems



Problems•A request to enter the current date and time

• Means that DOS did not find an AUTOEXEC.BAT file

• If you previously had one, investigate why and how you don’t now


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


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


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


Chapter Summary

Installing DOS• The MS-DOS Setup program will partition

and format a hard drive, if needed• Hardware requirements for MS-DOS are

minimal:• An IBM or compatible PC• 6MB of free hard disk space• 512KB of memory


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


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


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


Chapter Summary

Describe the DOS Bootup Process and Create Startup Disks• A soft boot of a PC occurs when you press

CTRL-ALT-DELETE• Many computers have a Reset button, which

resets a running computer without a power-down and power-up cycle


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


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


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:


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

McGraw-Hill/Irwin© 2006 The McGraw-Hill Companies, Inc. All rights reserved. 2-1.

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