Fall 2009 Lecture 2 Operating Systems: Configuration & Use C IS345 Disk Operating System (DOS) Mostafa Z. Ali Mostafa Z. Ali mzali@just.edu.jo 1-1
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 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 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 2-4
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 2-5
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 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 booting up a computer and running special diagnostic programs 2-7
Finding DOS and Understanding its Strengths and Weaknesses • DOS Weaknesses – Processor mode 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 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 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 personal computer • 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 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 2-13
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 2-14
Installing DOS Step ‐ by ‐ Step 2.01 Installing DOS on a Hard Disk Page 55 2-15
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 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 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. 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 bytes (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 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 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 time 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 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 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 Batch File Page 63 2-24
How the FAT File System Works •DOS File Attributes •Determine the manner in which DOS handles files – Read ‐ only – Hidden – Archive – Volume label – 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 Help in DOS Page 68 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 path 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 directory structure to save and organize files 2-33
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