Operating System Structure and System Files

 

Operating System Structure and System Files

Major Operating System Functions

·         Operating systems provide an interface through which you can interact with the computer system.

·         Operating systems provide the means by which you can store and organize data—one of the most fundamental computing requirements.

·         Operating systems provide printer subsystems and drivers so that you can print to a multitude of different printing devices.

·         Operating systems provide the ability to create, manage, organize, and secure data and programs.

·         Windows 9x and Windows Me are operating systems designed for use in non-business settings where an affordable OS that offers compatibility with a wide range of applications and hardware is required, but other features like advanced networking support and high levels of security are not required. Windows 9x and Windows Me are no longer supplied by Microsoft, having been replaced with Windows XP.

·         Windows NT was a robust operating system that built on the strengths of its predecessor, Windows NT 3.51 while implementing the new Windows 95–style interface. Windows NT 4 came in two primary versions—Windows NT Workstation, which was designed as a robust business-quality workstation operating system, and a server version designed as a corporate-level server operating system. Implementation of Windows NT was widespread and was largely responsible for establishing Microsoft in the server operating system market.

·         Windows 2000 is a business-level operating system that was released in a Professional edition designed for workstation use, and multiple server versions designed for corporate networking. Although Windows 2000 was built on Windows NT technologies, it came with many new features including support for Microsoft’s directory services system—Active Directory.

·         Windows XP is the most recent workstation operating system release from Microsoft. It comes in two versions—Windows XP Home Edition is designed to replace Windows 9x/Me and Windows XP Professional is designed to replace Windows 2000 Professional. Windows XP has a slightly different user interface but in general terms it shares many of the same features as its predecessors.

·         To see which version of Windows you are running, right-click My Computer and select Properties, or access the System Properties dialog box by double-clicking the System icon in Control Panel.

Major Operating System Components

·         Registry

o        The registry is a single hierarchical database that holds the system’s hardware and software settings.

o        The registry is the central location where all of the system configurations are kept.

o        In a Windows 9x system, the registry is made up of two files, System.dat and User.dat.

o        Changes are sometimes made manually to the registry using registry editors such as Regedit.exe and Regedt32.exe.

o        A common method of making changes to the registry is by using the utilities in Control Panel.

·         Virtual Memory

o        This is the name given to an area of space on the hard disk that is used by the operating system as if it were normal physical memory.

·         File Systems

o        File systems are the means by which data (in the form of files) is organized on storage devices such as hard disks and CDs.

o        The characteristics of a file system define such things as the maximum partition size, security measures, the permissible characters, and the organization of the files within folders.

o        Windows 9x supports the FAT16 file system and starting with Windows 95 OSR2 the FAT32 file system is supported as well.

o        Windows 2000 supports the FAT16, FAT32, and NTFS file systems.

Major Operating System Interfaces

·         Windows Explorer

o        Windows Explorer shows all of the drives connected to the system. Clicking on any of these drives allows you to see the files and folders held within the drive.

o        Files and folders in Windows Explorer are organized in a tree-like structure with parent folders containing other folders and files.

o        Windows Explorer gives you a method of easily copying and moving files and folders around the system.

o        To view hidden files in Windows, you can select Folder Options from the Tools menu in Windows Explorer.

·         My Computer

o        The My Computer window displays all of the installed system drives and shortcuts to some of the commonly accessed Windows utilities including Control Panel.

o        Selecting any of the drives in the My Computer window will open that drive and display the contents of that drive.

·         Control Panel provides access to the areas used to perform system tasks such as installing, managing, and configuring hardware and software on Windows-based systems. Inside Control Panel, several utilities can be accessed to start management programs including:

o        Add/Remove Programs:   Used to add or remove programs from the system. The Add/Remove Programs utility is also used in Windows 9x to create a startup disk.

o        Add New Hardware:   When new hardware is added to the system that is not detected by Plug and Play, use the Add New Hardware utility to add devices to the system. You can also use the Add New Hardware utility to troubleshoot an existing device.

o        Display:   The Display utility is used to customize the display settings for the system. From within the applet, the hardware acceleration settings are modified when troubleshooting video display problems such as system freezing.

o        Printers:   The Printers utility in Control Panel is used to add, remove, and configure the printers connected to the computer system. From the Printers utility you can also stop and restart print jobs you have sent to the printer.

o        System:   Some of the key areas accessed through the System Properties dialog box include: Device Manager, which shows the installed hardware in the system and its status; Hardware Profiles, which enable you to establish different hardware profiles on your computer (a setting typically used with laptop systems); and Performance Options, which allow you to optimize program response and change the system’s virtual memory.

o        Network or Network Connections:   The Network or Network Connections utility in Control Panel is where you go to configure the network. Options include adding and removing protocols, configuring network cards, and enabling file and print sharing.

·         Computer Management Console

o        The Computer Management utility is available in Windows 2000 and Windows XP. It allows you to perform system configuration and management tasks such as working with hard disks, user accounts, and other system settings.

·         Accessories/System Tools

o        The Accessories/System Tools program group contains many tools that are used in the maintenance and upkeep of the system. Which tools are included in this group will depend on the OS in use and the options installed.

·         Command Line

o        There are many command line utilities that can be used in the management of the system. The command line can be accessed through the Accessories program group or by launching Command.com (and/or Cmd.exe in Windows NT 4/2000/XP) from the Run dialog box.

·         Network Neighborhood/My Network Places

o        On a Windows 9x/NT 4 system, the Network Neighborhood utility allows you to view, or browse, the network and access resources. On Windows 2000 and Windows XP systems the utility is renamed My Network Places.

·         Taskbar/Systray

o        The taskbar provides a home for the Start button and the system tray (systray). In a default configuration the taskbar can be found at the bottom of the screen, but it can be repositioned at any edge of the screen. It can also be resized as necessary.

·         Start Menu

o        The Start menu is a pop-up menu present in all versions of Windows since Windows 95. The Start menu is intended as a way of easily accessing programs and utilities. The Start menu is activated by clicking the Start button on the taskbar.

·         Device Manager

o        Device Manager is used to identify what hardware has been detected by the system, the resources used by the device, and whether the device is currently functioning.

o        If a resource conflict is shown in Device Manager, you can manually change resources to correct the conflict.

o        Devices that are not recognized by the system or that are incorrectly configured will be displayed with a yellow circle that contains either a question mark or an exclamation point. A red X indicates that the device has been disabled.

Identifying Major System Files

·         Windows 9x core system files include the following:

o        Io.sys is located in the root directory (C:) and is responsible for loading system files and verifying their settings.

o        Msdos.sys contains the multiboot configuration for Windows 9x systems. Msdos.sys must be at least 1024 bytes (1 KB) in size.

o        Autoexec.bat is used during the boot process and contains the program and environment settings. Programs can be added and removed from the Autoexec.bat file using the Edit command or Sysedit from within Windows.

o        Command.com provides the command interface for the user. Basic commands such as Dir, Copy, and Cd are built into Command.com.

o        Config.sys is often used in conjunction with the Autoexec.bat file, but instead of handling the loading of programs, the Config.sys file is responsible for the loading of the device drivers and the configuration of the system’s memory. Though not needed with Windows 9x versions, it is still used for backward compatibility for those programs that need to access a Config.sys file to operate. Device drivers loaded into Config.sys are added with the line Device= or Devicehigh= followed by the device driver name. The Devicehigh option loads the devices into upper memory.

o        Himem.sys is an extended memory driver, which makes the memory area above 1 MB available for use by the operating system.

o        Emm386 is an expanded memory manager that works by deceiving the process into thinking that it is storing data in a special type of memory called expanded memory when in fact it is using extended memory.

o        Win.com is the startup file for Windows 9x. It is located in the root of the directory in which Windows is installed. There are a number of switches that can be used, but one of the most useful is /d, which causes Windows to start in safe mode.

o        System.ini is held in the Windows root directory and is included with Windows 9x for backward compatibility. The System.ini file stores data about the system’s hardware for use with DOS and Windows 3.x operating systems.

o        Win.ini holds program settings and personalized settings such as fonts, screen savers, and display settings. The Win.ini file is included for backward compatibility only.

o        System.dat is a registry file and maintains the settings for the system’s hardware including resource allocation, device drivers, and hardware configurations. The backup file of System.dat, System.da0, is held in the Windows folder and will be used by the system in the event that the System.dat file fails.

o        User.dat is the other file comprising the registry. User.dat holds only user-specific information such as passwords, personalized color settings, and installed programs. A backup file of User.dat, User.da0, is used should the original User.dat file become corrupt.

·         When you want to exclude a line from executing in the Config.sys or Autoexec.bat file, add a semicolon or the word Rem before the line and the entry will be ignored.

·         Editing text-based Windows files can be done using the Edit command-line program, and using Notepad or the Sysedit utility in Windows.

·         Windows NT/2000 core files include the following:

o        Boot.ini defines the location of the Windows NT and Windows 2000 system files.

o        Ntldr is responsible for loading the operating system.

o        Bootsect.dos holds the boot sector information of any other operating systems that are loaded on the system.

o        Ntdetect.com is responsible for detecting hardware and builds a hardware list.

o        Ntbootdd.sys is used only when the system boots from a SCSI device that does not have a BIOS installed.

o        Ntuser.dat is a file that stores a user’s settings. When the user logs on, the information in the Ntuser.dat file is placed in the registry.

o        A number of files comprise the registry. In a default installation they can be found in the C:\Winnt\System32\Config directory.

Using Command Line Functions

·         DOS commands are referred to as both internal and external commands. Internal commands are primary DOS commands and are built into the Command.com file. Internal commands include Dir, Cls, Copy, and Delete. External commands are not included in the Command.com file. Such commands include Xcopy, Attrib, and Edit.

·         Help for practically all DOS commands can be obtained by typing the command followed by the /? switch.

·         There are two wildcard characters you can use. The question mark (?) is used to denote a single character. The other permissible wildcard character is an asterisk (*), which is used to denote a group of characters.

Dir

·         The Dir command is used to list the contents of various directories. An example would be issuing dir windows from the root folder, which would give a listing of the files in the Windows directory.

Attrib

·         The Attrib command is used to view and modify the attributes of a file. File attributes include hidden (h), system (s), read-only (r), and archive (a). The + and – signs are used to add an attribute to or remove an attribute from a file or folder. An example of the Attrib command is attrib +h +r comptia.bat, which would change the attributes of the file Comptia.bat to hidden and read-only.

Ver

·         The Ver command is an internal DOS command used to identify which operating system version is being used on the system. The syntax is simply ver.

Mem

·         The Mem command is used to view the available memory including conventional, extended, and expanded memory. The simplest form of the command is mem.

ScanDisk

·         ScanDisk is a widely used utility and is used to detect and correct file problems and errors on hard disks and floppy disks.

·         During the ScanDisk operation, the hard disk is examined by looking for physical errors on it that will be marked as bad so no new data can be stored in that location.

Defrag.exe

·         The function of this utility is to rearrange the files on the disk in a contiguous fashion.

·         When using Defrag, you should really try to leave the system alone so that it can do its thing. Also, programs like virus checkers and screen savers can cause delays in the Defrag process because they use valuable system resources.

·         Defrag can improve the performance of a hard disk by better organizing its contents.

·         Defrag is not used to identify errors on a hard disk.

Edit

·         The Edit command is widely used as a text editor to modify the key system files and even create batch files. The command edit will open the editor.

Copy

·         The Copy command is used to copy a file from one location to another from the command line. For example, this command will copy a file from the floppy disk to the hard disk: copy a:\text.doc c:\.

Xcopy

·         The Xcopy command enables multiple directories to be copied at once. To copy subdirectories with the Xcopy command, the /s switch is used. Xcopy uses the same general command line syntax as the Copy command, but it includes many additional switches with added functionality.

Format

·         The Format command is used after a hard disk has been partitioned. The formatting process prepares the disk for use. The Format command can also be used to prepare a floppy disk for use.

Fdisk

·         The Fdisk command is used to partition a hard disk.

Setver

·         The Setver command is used to manually set the DOS version reported to a program. This is typically done for backward compatibility.

Scanreg

·         The Scanreg utility is used to make a backup copy of the system’s registry, restore a copy of the backed-up registry, or attempt to fix the registry. Scanreg is issued with one of three primary switches: Scanreg /fix, Scanreg /restore, or Scanreg /backup.

Md/Cd/Rd

·         The Make Directory command (Md) is used to create directories from the command prompt. The Change Directory command (Cd) is used to move around the file structure. The Remove Directory command (Rd) is used to remove a directory from the structure. Note that the directory must be empty before it can be removed with the Rd command.

Delete/Rename

·         The Delete command is used to delete a file or files. The Rename command is used to rename a file. The commands can be shortened to Del and Ren, respectively.

Deltree

·         The Deltree command can be used to remove multiple directories, populated or unpopulated, at the same time.

Type

·         The Type command is used to display text files on the screen. Its only feature is the display of files—you cannot edit files with the Type utility.

Echo

·         The Echo command is used to cause a string of characters to be displayed on the screen. Echo is commonly used in batch files to turn on and off the showing of messages on the screen.

Set

·         The Set command is used to set environment variables.

Ping

·         The Ping utility is used to test connectivity between two devices on a network running the TCP/IP protocol.

Managing Disks, Directories, and Files

Disk Management

·         Windows 2000 and Windows XP use the Disk Management utility found in the Computer Management console to manage hard disks.

·         Within the Disk Management utility in Windows 2000 and Windows XP, hard disks can be formatted with either the FAT16, FAT32, or NTFS file systems.

·         Windows 2000 and Windows XP can use both basic disks and dynamic disks.

·         Windows 9x uses the Fdisk utility to manage hard disks.

·         Disks can be formatted from within My Computer and Windows Explorer.

Partitioning, Formatting, and File Systems

·         Partitions are logical divisions of the hard disk. Each partition can be formatted with a file system. There are two types of partitions, primary and extended. Primary partitions can be made bootable, in which case they are referred to as active partitions. There can be only one active partition on a disk at a time.

·         Extended partitions can be further divided up into logical partitions.

·         A hard disk can have a maximum of four partitions on it, either four primary partitions, or three primary partitions and one extended partition.

File Systems

·         FAT16

o        The FAT16 file system will only recognize partitions up to 2 GB in size.

o        The FAT16 file system offers no local security on files and folders.

o        FAT16 partitions can be read and accessed by MS-DOS, Windows 3.x, Windows 9x, Windows NT, and Windows 2000/XP.

·         FAT32

o        FAT32 was introduced with Windows 95 OSR2.

o        FAT32 supports hard disk volumes up to 2 terabytes.

o        FAT32 does not offer local security for files and folders.

o        FAT32 does not support disk compression.

o        FAT32 uses more efficient cluster sizes than FAT16, often enabling it to store more files in a given amount of space.

o        Windows 9x since Windows 95 OSR2 supports FAT32; Windows 2000 and Windows XP support FAT32, but Windows NT 4 does not.

·         NTFS

o        NTFS partitions cannot be accessed on Windows 9x systems.

o        Security:   The NTFS file system allows for permissions to be applied to local files and folders.

o        Volume size:   NTFS allows for large volume sizes, and a maximum volume size of 2 TB.

o        Disk performance:   NTFS offers a higher level of performance than FAT, particularly with larger files.

·         NTFS5

o        NTFS5 was introduced with Windows 2000 and offers enhancements to earlier versions of NTFS.

o        Encryption:   Windows 2000 allows you to encrypt individual files and folders. Once a file or folder is encrypted, only those who have the decryption key can access it. Windows 2000 does this through a feature called the Encrypting File System (EFS).

o        Disk quotas:   Disk quotas are a means to restrict the amount of space that a user can use to save files on the system. Any Windows 2000 NTFS partition can support disk quotas.

·         HPFS

o        HPFS was not widely used in the Windows world and while ­Windows NT could read HPFS volumes, no other Windows OS offers support for HPFS. HPFS originated on the OS/2 platform.

·         CDFS

o        This is the standard format used by data CDs.

·         Converting File Systems

o        You can convert a FAT32 or FAT16 file system to NTFS on a Windows 2000/XP system using the following command: convert x: /fs:ntfs (where x is the drive letter you want to convert).

o        You can convert from a FAT16 file system in Windows NT 4 using the same command as in Windows 2000/XP.

o        NTFS cannot be converted back to FAT16 or FAT32.

o        FAT16 can be converted to FAT32 using the Cvt1.exe command.

Directory Structures

·         A directory structure provides a framework that allows you to organize files on a disk. At the very top of the directory structure is the root. This is reflected in commands such as the backslash (\). Under the root directory other folders are created. These are referred to as subfolders.

• Creating folders

You can create folders as you need them. There are a number of ways to create folders. The most common is now to create folders from within Windows Explorer, but you can also use the Make Directory command (Md) at the command prompt.

• Navigating the directory structure

You can navigate the directory structure from within Windows Explorer or by using the Change Directory (Cd) command at the command prompt.

Files

·         Files are typically created when you save a file through a program or when you copy files to or from your computer. You can also create new files by right-clicking in a folder in Windows Explorer and clicking New.

·         The most common file name extensions and their functions are listed in Table B-1.

Table B-1. Common File Name Extensions
File Name Extension	Associated Program or Function
.exe	Identifies an executable program. Examples of such files include Setup.exe and Install.exe.
.bat	Identifies an executable batch file. Batch files are used to run specific programs or sets of commands.
.com	Used to identify a command file. An example of a command file is Command.com.
.bmp	Identifies a graphics (bitmap) file.
.jpg	Identifies a graphics (JPEG) file.
.ini	Identifies an initialization file for a program. Good examples of .ini files include Win.ini and System.ini. These are text files and typically edited with the Sysedit utility.
.sys	Used with system files.
.doc	The file extension associated with Microsoft Word documents.
.txt	Documents saved in a text format.

·         Files with certain file names suggest that they are executable, that is, they can be run from the command line. Executable file name extensions include .bat, .exe, and .com. File names cannot include the following characters: \ / ? * : ” < > │

·         File Attributes

o        There are four attributes that can be assigned to individual files and folders: read-only (r), archive (a), system (s), and hidden (h). Table B-2 lists file and folder attributes.

Table B-2. File and Folder Attributes
Attribute	Description
Archive	When the archive attribute is applied, the file or folder will be marked for backup. Windows backup utilities can be set to back up files with the archive attribute set. By default, all files are assigned the archive attribute but folders will have to be done manually.
System	The system attribute is automatically assigned to key Windows and DOS files. System files are often also assigned the hidden attribute as an extra level of precaution.
Hidden	Files and folders assigned the hidden attribute will not be visible by default from within Windows or DOS.

o        Attributes are modified from the command line using the Attrib command. When removing attributes the minus (<;$MI>) sign is used, and when adding attributes the plus (+) sign is used.

·         In Windows, you can view and modify the attributes for a file simply by right-clicking on the file you wish to view and choosing Properties from the menu.

·         File Compression

o        File compression saves space on the hard disk by reducing a file to less than its original size. The compression algorithm is able to do this because the way that programs save files is not always the most efficient way of doing it. File systems like NTFS support file compression on a file-by-file basis.

·         File Encryption

o        File encryption is a process that scrambles the file so that only someone with the appropriate access rights can access it. File encryption is available through third-party products and with some Windows operating systems through the Encrypting File System (EFS) feature.

·         File Permissions

o        File permissions are attributes applied to files that denote who can perform what action to the file. NTFS supports the file permissions detailed in Table B-3.

Table B-3. NTFS File Permissions
Permission	Description
Full Control	Allows full access and control over the file including changing the permissions and ownership.
Modify	Allows the user to see, change, and delete existing files. If applied to a folder, also allows the creation of new files.
Read & Execute	Allows the user to see the file and its contents. If the file is an executable, the user can also execute that file.
List Folder Contents	Allows the user to see the files in a folder and their attributes but not to actually open the file.
Read	Allows the user to see the files in a folder and to open them, but not make any changes to the file.
Write	Allows a user to create new files and make changes to the contents of existing files. It does not allow the user to delete a file.

o        File permissions can be combined between users and groups but if a permission is denied through one or the other, it is not allowed.

·         File Types

o        There are two types of files used on a computer. Text files, which can contain a standard set of numbers and characters, and can be read in a text editor, and binary files, which store information in code. The latter should not be opened in a text editor because even a small change will affect its ability to be used.

Major Operating System Utilities

Backup and Restore

·         There are three primary backup types used:

o        A full backup saves all directories and files from the hard disk and does not use the archive bit to determine whether a file should be backed up. It does however clear the archive bit once the file or directory has been backed up.

o        An incremental backup includes only the files that have changed or been created since the last full or incremental backup. To determine whether a file has changed since the last full backup, the backup software looks at the archive bit setting on the file. Only files and folders with the archive bit set to on will be backed up. Once the file has been backed up, the archive bit is cleared so that the file is not backed up again unnecessarily.

o        Differential backups back up the files that have changed since the last full backup.

·         Chkdsk

o        Chkdsk is a utility that is used to check, and if necessary repair, the file system on a hard disk. It is a DOS-based utility.

·         Disk Cleanup

o        The Disk Cleanup feature in Windows 2000 and Windows XP scans your computer hard disk looking for files such as temporary files and temporary Internet files that can be deleted to free up space on the disk.

·         Format

o        The Format command is the tool used in the final step to prepare a disk for use. The Format command can be used on both hard and floppy disks.

·         Device Manager

o        Device Manager is used to identify what hardware has been detected by the system, the resources used by the device, and whether the device is currently functioning.

o        If a resource conflict is shown in Device Manager, you can manually change resources to correct the conflict.

o        Devices that are not recognized by the system or that are incorrectly configured will be displayed with a yellow circle that contains either a question mark or an exclamation point. A red X indicates that the device has been disabled.

·         Msconfig.exe

o        The Msconfig utility enables you to safely modify legacy Windows files without making permanent changes. It allows you to customize these files, determining which of the legacy files Windows is to use.

·         Regedit.exe

o        The Regedit utility enables you to navigate through the registry, modify and search through the values in the registry, and manually export the entire registry to create a backup.

o        Regedit is used by all versions of Windows since Windows 95.

o        Regedit can be used to export the registry for backup purposes and import that file when needed.

·         Regedt32.exe

o        This is a registry editing tool used on 32-bit operating systems like Windows NT 4 and Windows 2000.

o        When editing the registry, you normally use Regedit in Windows 9x and Regedt32 in Windows NT 4 and Windows 2000. Where possible, you should always try to configure the system through Control Panel rather than with a registry editor because it is safer.

·         Sysedit.exe

o        The Sysedit utility lets you edit the legacy system files simultaneously, including the Autoexec.bat, Win.ini, System.ini, Config.sys, and Protocol.ini files.

·         Event Viewer

o        The Event Viewer utility in Windows NT/2000/XP provides access to the various system logs. These provide useful information on how the system is running and any issues that have occurred.

·         Task Manager

o        The Task Manager can be activated by pressing Ctrl+Alt+Delete on a Windows NT/2000/XP Professional system and selecting Task Manager. Information provided by the Task Manager can help you determine the current state of the system and is useful in tracking down problems.

·         Attrib.exe

o        This command line utility is used to change or view the attributes of a file or folder.

·         Extract.exe

o        The Extract utility is used to manually extract Windows installation files.

o        The Extract utility must be run from the command line. To extract a compressed file, use the syntax extract followed by the file you wish to decompress.

o        Extract lets you retrieve a single file from a .cab file, which can be useful if a user deletes an important file by accident.

·         Edit.com

o        The Edit command is used as a text editor to modify the key system files and even create batch files. Issuing edit at a command prompt will open this simple text editor and allow you to save, print, and edit text files.

·         Windows Explorer

o        Windows Explorer is an all-in-one file management tool that allows you to create, delete, modify, and move files and folders through one interface.