1. 2 Disk Operating System (DOS) Finding DOS and Understanding its Strengths and Weaknesses...

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Disk Operating System (DOS)

Finding DOS and Understanding its Strengths and Weaknesses

Installing DOS

How the FAT File System Works

Working with the DOS Command Prompt

Understanding the DOS Bootup Process

Troubleshooting 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

DOS is Text base Operating System

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

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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 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

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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

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Finding DOS and Understanding its Strengths and Weaknesses 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

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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 computer 6MB of free hard disk space for the DOS utilities 512KB of memory

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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

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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

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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

Step-by-Step 2.01 Installing DOS on a Hard Disk Page 55

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FAT File System Components FAT Table

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

Cluster – minimum space allocated to a file

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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 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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FAT File System Components (continued) 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)

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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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FAT File System Components (continued) 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

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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

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DOS file-naming rules: A file name is up to eight characters, followed

by a period, and 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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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

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Read-only Archive System

Hidden Volume Label Directory

•DOS File Attributes (Demo)

•Determine the manner in which DOS handles files

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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

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Success at the DOS Prompt Success means correctly entering commands

and getting desired results Important for working with DOS and other OSs 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 /?

Step-by-Step 2.03 Using the Online Help in DOS Page 68

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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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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

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Working with the DOS Command Prompt 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

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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

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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

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

Step-by-Step 2.04 Managing Files and Directories Page 73

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Working with the DOS Command Prompt (dir /a)

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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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

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DOS system files (continued) DOS Configuration Files CONFIG.SYS – adds device drivers and modifies

DOS settingsBUFFERS DOS

DEVICE FILES

DEVICEHIGH STACKS

AUTOEXEC.BAT batch file loaded during bootupPATH PROMPT SET

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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

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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 Disk

Using FORMAT to create a startup disk Using SYS to create a startup disk Using Windows to create a startup disk

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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

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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:

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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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“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

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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


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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


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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

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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 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

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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 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

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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

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