Operating System — Overview

An Operating System (OS) is an interface between a computer user and computer hardware. An operating system is a software which performs all the basic tasks like file management, memory management, process management, handling input and output, and controlling peripheral devices such as disk drives and printers.

Some popular Operating Systems include Linux Operating System, Windows Operating System, VMS, OS/400, AIX, z/OS, etc.

Definition

An operating system is a program that acts as an interface between the user and the computer hardware and controls the execution of all kinds of programs.

Following are some of important functions of an operating System.

• Memory Management
• Processor Management
• Device Management
• File Management
• Security
• Control over system performance
• Job accounting
• Error detecting aids
• Coordination between other software and users

Memory Management

Memory management refers to management of Primary Memory or Main Memory. Main memory is a large array of words or bytes where each word or byte has its own address.

Main memory provides a fast storage that can be accessed directly by the CPU. For a program to be executed, it must in the main memory. An Operating System does the following activities for memory management −

Keeps tracks of primary memory, i.e., what part of it are in use by whom, what part are not in use.

In multiprogramming, the OS decides which process will get memory when and how much.

Allocates the memory when a process requests it to do so.

De-allocates the memory when a process no longer needs it or has been terminated.

Processor Management

In multiprogramming environment, the OS decides which process gets the processor when and for how much time. This function is called process scheduling. An Operating System does the following activities for processor management −

Keeps tracks of processor and status of process. The program responsible for this task is known as traffic controller.

Allocates the processor (CPU) to a process.

De-allocates processor when a process is no longer required.

Device Management

An Operating System manages device communication via their respective drivers. It does the following activities for device management −

Keeps tracks of all devices. Program responsible for this task is known as the I/O controller.

Decides which process gets the device when and for how much time.

Allocates the device in the efficient way.

File Management

A file system is normally organized into directories for easy navigation and usage. These directories may contain files and other directions.

An Operating System does the following activities for file management −

Keeps track of information, location, uses, status etc. The collective facilities are often known as file system.

Decides who gets the resources.

Allocates the resources.

De-allocates the resources.

Other Important Activities

Following are some of the important activities that an Operating System performs −

Security − By means of password and similar other techniques, it prevents unauthorized access to programs and data.

Control over system performance − Recording delays between request for a service and response from the system.

Job accounting − Keeping track of time and resources used by various jobs and users.

Error detecting aids − Production of dumps, traces, error messages, and other debugging and error detecting aids.

Coordination between other softwares and users − Coordination and assignment of compilers, interpreters, assemblers and other software to the various users of the computer systems.

User Interface Language Management

MUI allows your applications to manage user interface languages in two ways. An application can use a simple approach to language management by defaulting to the operating system language settings. Alternatively, the application can support its own languages from which the user can select. The MUI API also allows your application direct access to languages and language lists supported by the operating system and maintained by the resource loader. The remainder of this topic defines the system-supported languages and the language fallback mechanism.

Languages Maintained by the Operating System

System Default UI Language/Install Language

The system default UI language is the language of the localized version used to set up Windows. All menus, dialog boxes, error messages, and help files are represented in this language, except when the user selects a different language.

On WindowsВ Vista and later, the system default UI language is known as the «install language» and plays a more limited role. For most purposes, it is superseded by the system preferred UI languages. However, in certain contexts it is useful to have a single install language that is always known to be fully supported.

No MUI function is available to set the system default UI language. To retrieve this language, the application can call GetSystemDefaultUILanguage.

System UI Language

The operating system defines the system UI language as a user interface language that can be set by an administrator in the Advanced tab of the regional and language options portion of Control Panel. The operating system uses this language if the current user has not made specific language settings or if no active account is logged in. The language can be changed only if more than one user interface language is installed on the computer.

The operating system must be rebooted for all users and services to see the effect of the language change.

No MUI function is available to set the system UI language. To retrieve this value, an application targeted at WindowsВ Vista and later can call GetSystemPreferredUILanguages and obtain the first language in the system preferred UI languages list. Applications targeted at pre-WindowsВ Vista operating systems cannot use GetSystemPreferredUILanguages and should be based on the assumption that the system UI language is always the same as the system default UI language.

User UI Language

The user UI language determines the user interface language used for menus, dialog boxes, help files, and so forth. It can be set by the current user in the Language tab of the regional and language options portion of Control Panel. This language can be changed only if more than one user interface language is installed on the computer. Note that the user will have to log off and then log back on to see the effect. For example, a multinational corporation wants to deploy Windows in all of its subsidiaries. The company creates a global install job, which installs the English language version of Windows on all clients, regardless of location. At the same time, it installs specific language modules depending on the organizational unit of which a computer is a member. When the user logs on the first time to a newly installed operating system, Windows appears as a localized version.

On WindowsВ Vista and later, the user UI language is the first language in the user preferred UI languages list. Note that fallback languages can be used if particular resources are not available in this language.

On pre-WindowsВ Vista operating systems, the user UI language is usually the same as the system default UI language. However, for Windows MUI, the two languages can be different.

To retrieve the user UI language, an application can call GetUserDefaultUILanguage or GetUserPreferredUILanguages. The application cannot change the user UI language, as there is no function to set it.

Language Lists Maintained by the Operating System

System Preferred UI Languages List

The resource loader maintains a system preferred UI languages list. Included in this list are languages preferred by the operating system for its own resources, such as menus and dialogs, messages, INF files, and help files. The list is made up of the system default UI language and the system UI language and their fallbacks. An application can retrieve system preferred UI languages by calling GetSystemPreferredUILanguages.

User Preferred UI Languages List

The resource loader uses a user preferred UI languages list that includes languages that the user prefers. The resource loader uses resources matching languages from this list, if available, for a particular application thread. These languages take precedence over any system preferences. To retrieve user preferred UI languages, your application can call GetUserPreferredUILanguages.

Process Preferred UI Languages List

On WindowsВ Vista and later, the resource loader maintains a process preferred UI languages list consisting of up to five valid languages set by a running process for a MUI application. The languages can be set by the application with a call to SetProcessPreferredUILanguages. The application can retrieve the languages by calling GetProcessPreferredUILanguages.

Thread Preferred UI Languages List

On WindowsВ Vista and later, the resource loader uses a thread preferred UI languages list that consists of up to five valid languages set by a thread in a running process for a MUI application. These languages are used to customize the application user interface languages and make them different from the operating system language. The thread preferred UI languages list is based on the user preferred UI languages, the system preferred UI languages, and the system default UI language.

To set the thread preferred UI languages, the application should call SetThreadPreferredUILanguages. To retrieve these languages, the application calls GetThreadPreferredUILanguages.

Neutral Language Representation

A neutral language is represented as the language alone, without region or locale. For example, the neutral representation of the English (Canada) language, en-CA, is represented as «en». Even though a neutral language is not associated with the aspects of a region or locale, you can associate it with a resource set. Typically, a neutral language resource is based on the use in the most prevalent region for the language.

As an illustration, suppose that your MUI application localizes German language resources for German (Switzerland) represented as de-CH and German (Austria) represented as de-AT, while building a full set of resources for German (Germany) represented as de-DE. You must make decisions for this application considering entire resource files. If the application duplicates the de-DE resources as neutral language resources, it must provide a fallback language for the resource loader. If the loader does not find a particular language-specific resource file for de-CH or for de-AT, it falls back to the language-neutral «de» resources. These resources are most likely more appropriate than resources for a completely different language, for example, English (United States), which are the only other possible fallbacks.

As another example, an application might not localize at all for Belize. However, support of a language preference of English (Belize), represented as en-BZ, allows the application to fall back to «en» resources.

Language Fallback in the Resource Loader

WindowsВ Vista and later arrange user interface language settings in a preordered fallback language list used by the resource loader. To form the list, the operating system combines several languages, in the order shown:

Thread preferred UI languages, consisting of thread user interface language and its neutral form. Examples are fr-FR for French (France) and its neutral form «fr» and es-ES for Spanish (Spain) and its neutral form «es».

Process preferred UI languages, consisting of process user interface language and its neutral form. An example is de-DE for German (Germany) and its neutral form «de».

User UI language and its neutral form. An example is ja-JP for Japanese (Japan) and its neutral form «ja».

System UI language and its neutral form. An example is it-IT for Italian (Italy) and its neutral form «it».

This language is only included in the fallback list when the user UI language is not set.

System default UI language and its neutral form. An example is es-ES for Spanish (Spain) and its neutral form «es».

The following shows the merged fallback list. Note that the duplication of languages, for example, es-ES and es, is eliminated. Since the example sets the user UI language to ja-JP, the system UI language does not appear in the merged fallback list.

fr-FR, fr, es-ES, es, de-DE, de, ja-JP, ja

When loading resources for a MUI application, the resource loader tries to select one of the files matching the thread preferred UI languages list for the currently running application thread. If the resource loader cannot find a direct match between a selected language and the first language-specific resource in the merged fallback list, it checks the subsequent languages in the list until it finds an acceptable fallback.

If the resource loader finds no file that it needs, it must use a «guaranteed good» fallback language. For the MUI resource technology, the resource loader determines the fallback language from the provided resource configuration data. For more information, see MUI Resource Management.

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Operating system and user interface

As already mentioned, in addition to the hardware, a computer also needs a set of programs—an operating system—to control the devices. This page will discuss the following:

• There are different kinds of operating systems : such as Windows, Linux and Mac OS
• There are also different versions of these operating systems, e.g. Windows 7, 8 and 10
• Operating systems can be used with different user interfaces (UI) : text user interfaces (TUI) and graphical user interfaces (GUI) as examples
• Graphical user interfaces have many similarities in different operating systems : such as the start menu, desktop etc.

When you can recognize the typical parts of each operating system’s user interface, you will mostly be able to use both Windows and Linux as well as e.g. Mac OS.

The role of operating system in the computer

An operating system (OS) is a set of programs which ensures the interoperability of the hardware and software in your computer. The operating system enables, among other things,

• the identification and activation of devices connected to the computer,
• the installation and use of programs, and
• the handling of files.

What happens when you turn on your computer or smartphone?
– The computer checks the functionality of its components and any devices connected to it, and starts to look for the OS on a hard drive or other memory media.
– If the OS is found, the computer starts to load it into the RAM (Random Access Memory).
– When the OS has loaded, the computer waits for commands from you.

Different operating systems

Over the years, several different operating systems have been developed for different purposes. The most typical operating systems in ordinary computers are Windows, Linux and Mac OS.

Windows

The name of the Windows OS comes from the fact that programs are run in “windows”: each program has its own window, and you can have several programs open at the same time. Windows is the most popular OS for home computers, and there are several versions of it. The newest version is Windows 10.

Linux and Unix

Linux is an open-source OS, which means that its program code is freely available to software developers. This is why thousands of programmers around the world have developed Linux, and it is considered the most tested OS in the world. Linux has been very much influenced by the commercial Unix OS.

In addition to servers, Linux is widely used in home computers, since there are a great number of free programs for it (for text and image processing, spreadsheets, publishing, etc.). Over the years, many different versions of Linux have become available for distribution, most of which are free for the user (such as Ubuntu, Fedora and Mint, to name a few). See the additional reading material for more information on Linux.

Mac OS X

Apple’s Mac computers have their own operating system, OS X. Most of the programs that are available for PCs are also available for Macs running under OS X, but these two types of computers cannot use the exact same programs: for example, you cannot install the Mac version of the Microsoft Office suite on a Windows computer. You can install other operating systems on Mac computers, but the OS X is only available for computers made by Apple. Apple’s lighter portable devices (iPads, iPhones) use a light version of the same operating system, called iOS.

Mac computers are popular because OS X is considered fast, easy to learn and very stable and Apple’s devices are considered well-designed—though rather expensive. See the additional reading material for more information on OS X.

Android

Android is an operating system designed for phones and other mobile devices. Android is not available for desktop computers, but in mobile devices it is extremely popular: more than a half of all mobile devices in the world run on Android.

User interfaces

A user interface (UI) refers to the part of an operating system, program, or device that allows a user to enter and receive information. A text-based user interface (see the image to the left) displays text, and its commands are usually typed on a command line using a keyboard. With a graphical user interface (see the right-hand image), the functions are carried out by clicking or moving buttons, icons and menus by means of a pointing device.

Larger image: text UI | graphical UI

The images contain the same information: a directory listing of a computer. You can often carry out the same tasks regardless of which kind of UI you are using.

Text user interface (TUI)

Modern graphical user interfaces have evolved from text-based UIs. Some operating systems can still be used with a text-based user interface. In this case, the commands are entered as text (e.g., “cat story.txt”).

To display the text-based Command Prompt in Windows, open the Start menu and type cmd. Press Enter on the keyboard to launch the command prompt in a separate window. With the command prompt, you can type your commands from the keyboard instead of using the mouse.

Graphical user interface

In most operating systems, the primary user interface is graphical, i.e. instead of typing the commands you manipulate various graphical objects (such as icons) with a pointing device. The underlying principle of different graphical user interfaces (GUIs) is largely the same, so by knowing how to use a Windows UI, you will most likely know how to use Linux or some other GUI.

Most GUIs have the following basic components:

• a start menu with program groups
• a taskbar showing running programs
• a desktop
• various icons and shortcuts.