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A+ Certification : Operating Systems

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Introduction: 

A+ Certification may be obtained by passing A+ Essentials exam, and A+ Practical Applications exam  Note that a candidate needs to pass both the exams to obtain the certification.  Linux is not included in the A+ Certification exam, as it has an exam of its own (Linux+ Certification), offered by CompTIA. A brief notes on important concepts of A+ Certification Operating Systems is given in the following sections. With the latest release of A+ objectives, several topics in Windows Vista, Windows 7, Wireless networking and Security have been added.

1. OS Fundamentals

1.1 Major Operating System components, and interfaces

1.2 Major system files, and their purpose

1.3 Frequently used command line functions

1.4 Creating and Managing Disks, Directories, and Files

Disks - Partitions

  1. Active Partition

  2. Primary Partition

  3. Extended Partition

  4. Logical Partition

File Systems

  1. FAT16, 

  2. FAT32, 

  3. NTFS4, 

  4. NTFS5.x

Files

  1. Creating files

  2. File naming conventions (Most common extensions, 8.3, maximum length)

  3. File attributes - Read Only, Hidden, System, and Archive attributes

File Attributes:

1.5 Some Operating System Utilities

Disks - Partitions

    Partitioning is the process of dividing and naming the hard disk so that the Operating System can recognize the media for further processing. There can be one or more partitions in a given hard disk. A maximum of four partitions can be placed on any hard disk.  These are called primary partitions. Only one partition may be designated, at any given time, as active. The primary partition will be used for booting the system. DOS  will only recognize the active primary partition. Any other primary partitions will be ignored. One of the four partitions may be designated as an extended DOS partition. This partition may then be subdivided into multiple logical partitions. 

  • Directory Structures (root directory, subdirectories, etc)

  • Create folders

  • Navigate the directory structure

The directory structure consists of Root directory, other directories, sub-directories, and files. The root directory is at the root of the file system. It is intuitive to navigate, create, and delete directories using Windows Operating System. While using DOS, you need to use command line interface (CLI) for the same. The following commands are used in DOS for navigating the file system:

C:>cd files

C:/files>md dir1

C:/files>rd dir1

The command "cd" is used to change the present working directory to "files". 

The command "md" is used to create a new directory by name "dir1"; md is short for make directory.

The command "rd" is used to remove the specified directory; rd is short for remove directory.

Another command frequently used is "dir", as shown below.

It lists all directories and files with the given path. In the example above, the command is given at the root directory (C:).

Files Systems: 

  • FAT16, 

  • FAT32, 

  • NTFS4, 

  • NTFS5.x

FAT: The FAT or FAT16 file system is used to store data on a disk. The FAT file system is better suited for smaller capacity hard disk drives. It supports a single partition up to a maximum size of 2GB.

FAT32: FAT32 can support hard disk drives larger than 2GB (maximum 2TB) without having to use multiple partitions. 

File Systems

Supported By

Supports Long File Names?

Supports File-level Security?

File Allocation Table (FAT or FAT16)

DOS, All versions of Windows

No

No

File Allocation Table, 32 BIT (FAT32)

DOS v7 and higher,
All versions of Windows

Yes

No

NTFS (New Technology File System)

Windows NT/XP/2000/2003 Server

Yes

Yes

NTFS5 (New Technology File System)

Windows XP/2000/2003 Server

Yes

Yes

 

Limitations of Different File Systems *

 

NTFS5

NTFS4

FAT32

FAT16

FAT12

Max Volume Size

2TB

2TB

Up to 2TB

Up to 4 GB

16MB

Max Files on Volume

Nearly Unlimited

Nearly Unlimited

4194304

65536

 

Max File Size

Limit Only by
Volume Size

Limit Only by
Volume Size

4GB minus 2 Bytes

2GB (Limit Only
by Volume Size)

16MB (Limit Only
by Volume Size)

Max Clusters Number

Nearly Unlimited

Nearly Unlimited

4177918

65520

4080

Max File Name Length

Up to 255

Up to 255

Up to 255

Standard - 8.3
Extended - up to 255

Up to 254

Courtesy: http://www.ntfs.com/ntfs_vs_fat.htm

FAT16 to FAT32 Conversion:

FAT16 file system can be converted to FAT32 using conversion utilities such as CVT1.EXE.

Please note that the following before proceeding with file system conversion: from FAT16 to FAT32:

 - After conversion to FAT32, the hard disk drive cannot revert to FAT16.

- You need to decompress a drive before conversion, as it is not possible to convert a compressed drive.

- Removable disks that have been formatted with FAT32 may not be recognized by other operating systems such as Linux.

- If any older Operating System exists (such as DOS or Win 95) on your computer (possible in multiple boot environment), your system may not be able to boot to it after a conversion to FAT32.


FAT to NTFS Conversion:


"convert" command converts FAT (usually means FAT16) and FAT32 volumes to NTFS. You cannot convert the current drive. If convert cannot lock the drive it will offer to convert it the next time the computer restarts.

convert [drive:] /fs:ntfs [/v]

Parameters

drive:

Specifies the drive to convert to NTFS.

/fs:ntfs

Specifies that the volume be converted to NTFS.

/v

FILES:

  • Creating files

  • File naming conventions (Most common extensions, 8.3, maximum length)

  • File attributes - Read Only, Hidden, System, and Archive attributes

A user may create files by using any text editor or any other program such as Microsoft Word. A file basically consists of two parts. These are:

  • File Name: The given name of the file. When using conventional DOS, this part of the file name must be between one and eight characters in length. 

  • File Extension: The extension of the file is usually set by the system based on the program used for creating the file. The extension is optional, and can be from zero to three characters long.

Since the file name is limited to maximum eight characters and the extension to three, the conventional DOS naming scheme is often called 8.3 naming. Windows Operating Systems automatically assign file extension (you can still manually over-ride the system, if you want to), and use appropriate program automatically to open the file when clicked. For example, if the file extension is .txt, the default text editor is launched when the file is double clicked. A .htm extension will launch default browser when clicked.

Long File Names (LFNs) are supported by Windows 9x, and later Windows Operating Systems. The following conditions are met with LFNs:

  • Windows Operating Systems and applications written for Windows could use file names much longer than 11 total characters.

  • The long file names could be stored on existing DOS volumes using standard directory structures.

  • Older pre-Windows software would be able to access the files that use these new file names.

File Attributes:

Important File attributes supported by DOS are given below:

Read-Only: With a file marked Read-Only, most software will refuse to delete or modify it. For example, DOS will give "Access denied" message if you try to delete a read-only file. 

Hidden: If the file is marked hidden then it is hidden from viewing using the "DIR" command. DOS will not display the file when you type "DIR" unless a special flag is used.

System: This flag is used to tag important files that are used by the system and should not be changed or removed from the disk. In essence, this is like more like a read-only flag.

Volume Label: Every disk volume can be assigned an identifying label, either when it is formatted, or later through various tools such as the DOS command "LABEL". The volume label is stored in the root directory as a file entry with the label attribute set.

Directory: This is the bit that differentiates between entries that describe files and those that describe subdirectories within the current directory. 

Archive: Backup software usually allows the user to do an incremental backup, which only selects for backup any files that have changed since the last backup. The Archive bit is used for this purpose. When the backup software backs up ("archives") the file, it clears the Archive bit. Any subsequent modification to the file will make the archive bit set. When the backup software runs again, it knows that the file has been modified since previous back-up, and backs it up again (and ofcourse, clears the archive bit).

In DOS, you can use ATTRIB command to modify any file attributes. Using Windows, by looking at the file's properties through Windows Explorer (or any similar software), you can modify file attributes. 

  • File Compression

  • File Encryption

File compression is a technique that compresses program or data files so that they occupy less disk space. The file is decompressed before use. Note that recompressing an already compressed file usually makes the file slightly larger due to compression overhead. File compression can be performed by the operating system automatically, or it can be manually performed using a file compression program. Examples of file compression programs are winzip, and pkzip.

File encryption is the process of encoding information in order to make it secure from unauthorized access, particularly during transmission. File decryption is done to reverse the encryption before using the file.  There are mainly two types of encryption schemes. One is based on Symmetric Keys, and the other is based on Asymmetric Keys. 

Windows 2000 uses compression similar to DriveSpace in windows 98, but unlike DriveSpace which compress entire volumes, it can compress individual files and folders.

Using Windows 2000, you can compress files and folders only on drives formatted with NTFS. Note that compressed files and folders cannot be encrypted.

If you add or copy a file into a compressed folder, it is compressed automatically. If you move a file from a different NTFS drive into a compressed folder, it is also compressed. However, if you move a file from the same NTFS drive into a compressed folder, the file retains its original attributes.

To compress a file or folder

1. In explorer select the file or folder you want to compress, then right click -> Properties
2. Check on the "Compress contents to save disk space"

To remove compression from a file or folder, just uncheck the "Compress contents to save disk space box"

Encryption: Windows 2000 includes greater security than other versions of windows, with its Encrypting File System (EFS). It is based on public and private key encryption. The file system automatically generates an encryption certificate for the user along with a private key. You can encrypt individual files or folders, only on the NTFS file system.

When a user is logged on, they don't have to decrypt files to use them EFS automatically detects an encrypted file, locates the users private key and decrypts the file.

To encrypt a file or folder

1. In explorer select the file or folder you want to encrypt, then right click -> Properties
2. Choose advanced button to display the advanced attributes
3. Check the "Encrypt Contents To Secure Data" box

To remove encryption from a file or folder, just uncheck the "Encrypt Contents To Secure Data" box.

You can also encrypt file and folders from the DOS command prompt using cipher.exe If you do not use any command line options cipher will just display the encryption status of the folder.

cipher [/e | /d] [/s:dir] [/i] [/q] [dirname]

- /e Encrypts specified directory
- /d Decrypts specified directory
- /s : dir Specifies the directory to encrypt or decrypt
- /i Ignors errors
- /q Specifies a directory
- dirname

Viewing hidden files:

System files and other important files that normally do not require user edits are hidden by the Operating System. You can view these files by using Windows Explorer -> Tools -> Folder Options. Select show hidden files and folders button. 

The figure above shows the option using Windows 2000 Operating System.

 

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