2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

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

16. 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

17. 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.

18. 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)

19. 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

20. 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

21. 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

22. 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

23. 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

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

25. 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

26. 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

27. 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

28. 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

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

30. 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 /?

31. 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

32. 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

33. 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

34. 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

35. 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

36. 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

37. 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

38. 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

39. Working with the DOS Command Prompt
Step-by-Step 2.04
Managing Files and Directories
Page 73

40. 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.

41. 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

42. 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

43. 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)

44. 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

45. 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

46. 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

47. 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

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

49. 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:

50. 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

51. 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

52. 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

53. 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

54. 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

55. 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

56. 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

57. 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

58. 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

59. 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

60. 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

61. 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

62. 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

63. 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

64. 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

65. 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:

66. 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