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Home , Booting, Boot disk, Boot sector, Conventional memory, DELTREE, Directory structure

Fall 2009

Lecture 2

Operating Systems: Configuration & Use CIS345

Disk (DOS)

Mostafa Z. Ali [email protected]

1-1 Chapter 2

Disk Operating System (DOS)

Finding DOS and Understanding its Strengths and Weaknesses Installing DOS How the FAT Works Working with the DOS Prompt Understanding the DOS Bootup Troubleshooting Common DOS Problems 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 2-3 Finding DOS and Understanding its Strengths and Weaknesses • Versions of DOS – CP/M was an important predecessor to DOS – Many versions of DOS, several introduced by (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

2-4 Finding DOS and Understanding its Strengths and Weaknesses

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

2-5 Finding DOS and Understanding its Strengths and Weaknesses • DOS’ Strengths – DOS for with DOS apps – DOS when you need a small OS – DOS is 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

2-6 Finding DOS and Understanding its Strengths and Weaknesses

• 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 up a and running special diagnostic programs

2-7 Finding DOS and Understanding its Strengths and Weaknesses • DOS Weaknesses – Processor limits – Memory limits – Multitasking limits – Hard drive limits

2-8 Finding DOS and Understanding its Strengths and Weaknesses

• DOS Weaknesses (continued) – Processor Mode Limits • Only supports of operation of Intel processors » Newer Intel processors in the real mode, and newer OSs (Windows, , ) switch the processor from the real mode to the – Memory Limits • Intel processors in real mode use only 1 MB • 640 KB of RAM () is workspace for the OS, applications and data • 384 KB of addresses reserved for system BIOS and

RAM and ROM on adapters 2-9 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

2-10 Installing DOS

• DOS Hardware Requirements – The general DOS hardware requirements for MS‐DOS 6.22 and IBM PC‐DOS • An IBM or compatible • 6MB of free hard disk space for the DOS utilities • 512KB of memory

2-11 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

2-12 Installing DOS

• Partitioning a Hard Disk in MS‐DOS – Physical is done the factory – (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 2-13 Installing DOS

• Partitioning a Hard Disk in MS‐DOS (continued) – –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

2-14 Installing DOS

Step‐by‐Step 2.01

Installing DOS on a Hard Disk

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2-15 How the FAT File System Works

• FAT File System Components – FAT Table • (FAT) –DOS records disk space usage • Cluster – minimum space allocated to a file

2-16 How the FAT File System Works

• FAT File System Components (continued) – FAT12, FAT16, and FAT32 • FAT16 –used on hard disks • FAT32 – available since 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.

2-17 How the FAT File System Works

• FAT File System Components (continued) – How Cluster Size Affects Partitions • FAT16 file system limited to 65,525 clusters • Maximum cluster size 32,768 (32K) • 65,525 x 32,768 = 2GB (maximum partition size supported by the FAT16 file system)

2-18 How the FAT File System Works

• FAT File System Components (continued) – Root and Other Directories • The FAT and the 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 reference to the FAT table • Root directory is the top level directory

2-19 How the FAT File System Works

• 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 and date of its creation or modification, its size, attributes, and beginning cluster information

2-20 How the FAT File System Works

• Using a Directory and the FAT Table to 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

2-21 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

2-22 How the FAT File System Works

• 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

2-23 How the FAT File System Works

Step‐by‐Step 2.02

Creating a Simple

Page 63

2-24 How the FAT File System Works

•DOS File Attributes •Determine the manner in DOS handles files

– ‐only – Hidden – Archive – – System – Directory

2-25 How the FAT File System Works

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

2-26 How the FAT File System Works

• 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

2-27 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

2-28 Working with the DOS Command Prompt

Step‐by‐Step 2.03

Using the Online in DOS

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2-29 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 /?

2-30 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

2-31 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 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

2-32 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 to save and organize files

2-33 Working with the DOS Command Prompt • Learning to Manage Files and Directories (continued) – Designing a Directory Structure for File Management • DOS directory/folder structure is hierarchical • Drive | Directory | File Name • command can be used to view the entire directory structure • Store data in a separate directory from applications

2-34 Working with the DOS Command Prompt • Learning to Manage Files and Directories (continued) – Creating and Removing Directories • MD (Make Directory) will create a directory • or CHDIR (Change Directory) allows movement between directories • RD (Remove Directory) deletes an empty directory

2-35 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

2-36 Working with the DOS Command Prompt • Learning to Manage Files and Directories (continued) – Use File management commands (continued): • (Directory), MD, CD, (CLear Screen), , (REName), RD, and TYPE are some of the internal commands • XCOPY, , and DELTREE are often‐used external commands

2-37 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. DOS DIR /P List data one page at a time. commands and their CD .. Moves to the parent directory from the present directory. functionality

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. 2-38 Working with the DOS Command Prompt

Step‐by‐Step 2.04

Managing Files and Directories

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2-39 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.

2-40 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 DOS – COMMAND.COM is the command interpreter

2-41 Understanding the DOS Boot‐Up Process and Startup Disks

• DOS system files (continued) – DOS Configuration Files – CONFIG.SYS – adds device drivers and modifies DOS BUFFERS DOS DEVICE FILES DEVICEHIGH STACKS – AUTOEXEC.BAT batch file loaded during bootup PATH PROMPTSET

2-42 Understanding the DOS Boot‐Up Process and Startup Disks • 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 the system (a warm boot)

2-43 Understanding the DOS Boot‐Up Process and Startup Disks

• 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 – The bootstrap loader is a small program in the ROM BIOS

2-44 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 from the logical drive, which, in turn, runs the operating system loading program

2-45 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

2-46 Understanding the DOS Boot‐Up Process and Startup Disks • 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

2-47 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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2-48 Understanding the DOS Boot‐Up Process and Startup Disks • 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 a:

2-49 Understanding the DOS Boot‐Up Process and Startup Disks • Using Windows to Create a Startup Disk – In Windows 95 and 98 go to | 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

2-50 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

2-51 Troubleshooting Common DOS Problems • “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

2-52 Troubleshooting Common DOS 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

2-53 Troubleshooting Common DOS 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

2-54 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 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

2-55 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 , 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 2-56 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 – DR‐DOS is now sold through DeviceLogics – Versions of DOS can be found for free on the Internet 2-57 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

2-58 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 of file – File attributes determine how DOS handles a file or directory – File attributes are read‐only, archive, system, hidden, volume label, and directory 2-59 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, , 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 2-60 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

2-61 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

2-62 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 : 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

2-63 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

• Format a floppy disk in Windows XP 2-64 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: 2-65 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 . Create one, even if it is empty, and most PCs will use the internal clock for the time

2-66