Disk Operating System (DOS) Chapter 2 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

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

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 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

Finding DOS and Understanding its Strengths and Weaknesses 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

Finding DOS and Understanding its Strengths and Weaknesses 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

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 booting up a computer and running special diagnostic programs

Finding DOS and Understanding its Strengths and Weaknesses DOS Weaknesses Processor mode limits Memory limits Multitasking limits Hard drive limits

Finding DOS and Understanding its Strengths and Weaknesses 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

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

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 on a Hard Disk 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

How the FAT File System Works 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.

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 bytes (32K) 65,525 x 32,768 = 2GB (maximum partition size supported by the FAT16 file system)

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 reference to the FAT table Root directory is the top level directory

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

How the FAT File System Works 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

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

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

How the FAT File System Works Step-by-Step 2.02 Creating a Simple Batch File Page 63

How the FAT File System Works DOS File Attributes Determine the manner in which DOS handles files Read-only Archive System Hidden Volume label Directory

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

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

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

Working with the DOS Command Prompt Step-by-Step 2.03 Using the Online Help in DOS Page 68

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 /?

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

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 path

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

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 TREE command can be used to view the entire directory structure Store data in a separate directory from applications

Working with the DOS Command Prompt Learning to Manage Files and Directories (continued) 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

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

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

Working with the DOS Command Prompt 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

Working with the DOS Command Prompt 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.

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

Understanding the DOS Boot-Up Process and Startup Disks DOS system files (continued) DOS Configuration Files CONFIG.SYS – adds device drivers and modifies DOS settings BUFFERS DOS DEVICE FILES DEVICEHIGH STACKS AUTOEXEC.BAT batch file loaded during bootup PATH PROMPT SET

Understanding the DOS Boot-Up Process and Startup Disks 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)

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

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

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

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

Understanding the DOS Boot-Up Process and Startup Disks Step-by-Step 2.05 Create a Startup Floppy Disk Using FORMAT Page 83

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 sys a:

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

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

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

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

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

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