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CompTIA® A+™ Core 1 Exam Notes :Annexure : Ms Dos

6. ANNEXURE

Note : As per new syllabus topic Operating system has been moved to A+ Practical Application syllabus. This information is provided for your quick reference.

6.1 MS DOS

The following DOS utilities are useful in proper maintenance of PCs.

SCANDISK :ScanDisk is a utility program that was added to DOS Version 6.0. SCANDISK is a better compared to CHKDSK. SCANDISK can fix errors on data storage devices such as hard disks, floppy disks, RAM drives etc, and DoubleSpace compressed drives. It analyzes and repairs damage to the following:

  1. 1. Physical clusters

  2. 2. File allocation table (FAT)

  3. 3. Lost clusters

  4. 4. Cross-linked files

  5. 5. Directory tree

  6. 6. MS-DOS Boot sector

  7. 7. DBLSPACE volume header, file structure, compression structure.

CHKDSK (Check Disk) : CHKDSK command, one of DOS commands, examines your hard drive for error conditions and reports the total size of the disk, how many files are stored there, and the space remaining. CHKDSK also reports the total amount of conventional memory in your system and the amount of conventional memory available. Note that CHKDSK can't report extended memory.

DFRAG : The DFRAG.EXE is included with DOS6.0 and later. DEFRAG utility arranges the clusters of data on the hard drive to achieve better performance by placing all of the clusters for a given file together in a contiguous order. DEFRAG does not do any repair on your disk, and errors, if any will remain on the disk.

BACKUP : DOS has a backup utility since version 2.0. .COM, .EXE, .BAT files are executable files.

Important DOS files used during BOOT Up are:

  1. A. AUTOEXEC.BAT

    1. 1. It does: Modifies the PC environment (PATH, SET, and other commands)

    2. 2. Default Attributes: Nil

    3. 3. Is it required for OS Start up: NO

  2. B. CONFIG.SYS

    1. 1. It does: Loads low level device drivers and does performance tuning

    2. 2. Default Attributes: Nil

    3. 3. Is it required for OS Start up: NO

  3. C. IO.SYS

    1. 1. It does: Loads basics Input/ Output routines for the processor

    2. 2. Default Attributes: Hidden / System/ Read Only 3. Is it required for OS Start up: YES

  4. D. MSDOS.SYS

    1. 1. It does: Defines System File locations

    2. 2. Default Attributes: Hidden / System/ Read Only

    3. 3. Is it required for OS Start up: YES

  5. E. COMMAND.COM

    1. 1. It does: The file contains internal command set and error messages

    2. 2. Default Attributes: Nil

    3. 3. Is it required for OS Start up: YES

    4. 4. Responsible for displaying the command prompt in a DOS based computer.

  6. F. HIMEM.SYS

    1. 1. HIMEM.SYS must be loaded before EMM386.EXE

    2. 2. HIMEM.SYS is used to address the extended memory

  7. G. EMM386.EXE : EMM386.EXE allows access to Upper Memory Area. Please note that the conventional memory of 1 MB is divided into 1. Lower Memory Area 640 KB, and 2. Upper Memory Area 384KB (1024KB-640KB).

  8. H. ANSI.SYS

  9. 1. The files AUTOEXEC.BAT, CONFIG.SYS, ANSI.SYS are not required for OS start-up. However, the files IO.SYS, MSDOS.SYS, COMMAND.COM are required for OS start-up.

  10. 2. To bypass the CONFIG.SYS, and AUTOEXEC.BAT files during boot process of DOS, you need to press F5. F8 allows you to selectively bypass commands in AUTOEXEC.BAT, and CONFIG.SYS.

DOS allows you to set the following attributes using ATTRB command:

  1. 1. System

  2. 2. Hidden

  3. 3. Read-only

  4. 4. Archive

    1. '+' sets and attribute

    2. '-' clears an attribute

    3. Examples:

    4. The command ATTRIB +H myfile.txt will make the file myfile.txt hidden. The other attributes that can be set using ATTRIB command are System, Read Only, and Archive.

    5. The command ATTRIB C:\private.txt +h +r will mark the file private.txt as both hidden and read only.

DOS, Windows3.1 Windows 95/ 98 operating systems have the following characteristics:

  1. 1. Each can have only one primary partition per hard disk

  2. 2. The primary partition is automatically assigned a drive letter

  3. 3. Each hard disk can have only one Extended partition

  4. 4. You can create one or more logical drives in the Extended partition.

  5. 5. The drive letters are assigned manually to logical drives.

The standard DOS partition cluster sizes are as given below:

  1. 16MB-127MB: 2KB cluster size

  2. 128MB-255MB: 4KB cluster size

  3. 256MB-511MB: 8KB cluster size

  4. 512MB-1023MB: 16KB cluster size

  5. 1024MB-2048MB: 32KB cluster size

Note that due to DOS limitation, the FAT on each hard drive partition can have 64K (65535) individual addresses. Therefore, it is clear, depending on the size of partition, this number dictates the size of each cluster. We arrive at 32KB cluster size by dividing 2048(MB) with 64(KB).

The Windows 95/98 system files include the following : IO.SYS, MSDOS.SYS, WIN.INI, COMMAND.COM, SYSTEM.INI, SYSTEM.DAT, USER.DAT

  • MSDOS.SYS, WIN.INI, SYSTEM.INI are text files.

  • SYSTEM.DAT, USER.DAT files are part of windows Registry and can be edited using REGEDIT or REGDT32 utility. Registry files can't be read with standard text editors.

  • Further, USER.DAT file corresponds to HKEY_LOCAL_USER and SYSTEM.DAT corresponds to HKEY_LOCAL)MACHINE.

  • HKEY_LOCAL_MACHINE is the hive where the information specific to the machine will be stored. The information may include, network settings, hardware drivers etc.

  • HKEY_LOCAL_USER hive stores data specific to user configuration, such as desktop color schemes, screen savers, wall paper, and user specific application settings.

Using FDISK, the following activities can be carried out:

  1. 1. Create Partitions: You can create primary and extended partitions. Extended partition holds one or more (Up to 23) logical drives.

  2. 2. Set Active Partition: FDISK allows you to mark the primary partition as active partition.

  3. 3. Delete Partition: You can delete a partition by using FDISK

  4. 4. Display Partition Information.

DOS COMMANDS

MEMMAKER can be used to manage the system memory optimally. Windows 95 and above automatically manage the memory, where as DOS requires manual memory management using utilities like MEMMAKER. The DOS command MEM can only display the contents of memory, but itself can't manage the memory.

When you power on the DOS machine, you see a message, "Starting MS-DOS". If you press F5 key during this short period, you can bypass AUTOEXEC.BAT and CONFIG.SYS files.

Given below are common DOS commands that you use frequently:

  1. 1. PATH: The command sets or displays a path for executable files. For example, "PATH=C:\; C:\DOS; C:\PROG; C:\MYFILES " command indicates DOS to first search ROOT, then C:\DOS, then C:\PROG, and finally C:\MYFILES for executable files.

  2. 2. SET: Displays, sets, or removes DOS environment variable.

  3. 3. PROMPT: Changes the DOS command prompt. The prompt can be made up of normal characters and the following special codes:

    1. $p Current drive and path

    2. $l < ( less than sign)

    3. $d Current date

    4. $t Current time

    5. $_ Carriage return

    6. Syntax: PROMPT [text]

    7. For example, to set the prompt to current date, followed by the current drive path, issue the command:

    8. PROMPT= $p$d

The file load order to start DOS is : IO.SYS - > MSDOS.SYS -> CONFIG.SYS -> COMMAND.COM -> AUTOEXEC.BAT

Note that CONFIG.SYS, and AUTOEXEC.BAT are optional to load DOS. IO.SYS, MSDOS.SYS, COMMAND.COM are required.

When you format a disk with a "/s" switch (say “format a:/s”), the following files get transferred:

  1. 1. IO.SYS

  2. 2. MSDOS.SYS

  3. 3. COMMAND.COM

If you want to format a drive and also make it bootable, you need to format with /s switch.

6.2 Windows 95

1. The minimum published requirements for running Windows 95 is 386 processor with 4 MB of RAM. Though it may be sufficient, the performance will be very poor and some applications may not run at all. A recommended configuration is a Pentium processor with 32 MB of RAM.

2. Booting Windows 95 in safe mode loads the drivers for Keyboard, Mouse, and standard VGA graphics adapter.

3. Windows 95 Version A supported only FAT16 file system. The maximum hard disk partition supported by FAT16 is only 2 GB. However, Windows 95 Version B and Windows 98 support FAT32 and therefore, can support partitions upto 2TB (Tera bytes).

4. SYSTEM.DAT and USER.DAT comprise of Windows 95 Registry. These are the files where most of the user and system configuration information is stored. The Windows Registry files are stored in \Windows directory by default.

5. Windows 95 makes a backup of the Registry after every successful reboot. The Registry back up files are named: USER.DA0, SYSTEM.DA0. The original Registry files are named: USER.DAT, SYSTEM.DAT. It may be noted, that in the event of boot failure, you can delete the original USER.DAT AND SYSTEM.DAT files and the back up files can be renamed to DAT files and the system can be rebooted successfully.

6. While booting Windows 95, if you press F8, boot menu will be displayed. Windows 95 provides three different modes that the system can be started.

  1. a. Normal Mode: Normal Mode is the mode Windows 95 starts by default. It provides full functionality.

  2. b. Safe Mode: Safe Mode is a diagnostic mode of Windows 95 that starts Windows 95 without any network, CD ROM, and other drivers. The only device drivers loaded in Safe mode are:

    • Keyboard

    • VGA Display

    • Mouse Drivers

  3. c. Command Prompt: Command Prompt mode is provided to run some old DOS applications that need to be run under DOS only. These applications are primarily the ones which access hardware, that Windows 95 does not allow to be accessed otherwise. Command Prompt mode is also useful for running FDISK and MSD

7. The log file BOOTLOG.TXT records all the devices and drivers that the Operating System attempts to load. BOOTLOG records the status of the devices and drivers.

8. ScanDisk can be used to check disk drives for errors. The /f switch allows ScanDisk to automatically fix the errors.

9. HKEY_CURRENT_CONFIG stores the hardware settings. The six register keys available in Windows 95/98 Registry are:

  1. A. HKEY_CLASSES_ROOT

  2. B. HKEY_CURRENT_USER

  3. C. HKEY_LOCAL_MACHINE

  4. D. HKEY_USERS

  5. E. HKEY_CURRENT_CONFIG

  6. F. HKEY_DYN_DATA

10. Adding $ sign to the end of the share name makes the share invisible over the network.

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