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

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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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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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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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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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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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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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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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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 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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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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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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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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Step-by-Step 2.02

Creating a Simple Batch File

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Read-only

Archive System

Hidden Volume

label Directory

•DOS File Attributes

•Determine the manner in which DOS handles files

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LABEL commandCreates or changes a volume label (name) If a volume has a label, FORMAT requires

the name before reformatting

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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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Step-by-Step 2.03

Using the Online Help in DOS

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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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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 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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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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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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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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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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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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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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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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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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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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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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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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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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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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Step-by-Step 2.05

Create a Startup Floppy Disk Using FORMAT

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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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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


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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 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

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CSC 2260 Operating Systems and Networks