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Computer Operating Systems

Objective   2/14/2016

To provide resource information on the most popular Operating Systems.

What IS an Operating System ?   4/25/2016

The History of Operating Systems

An operating system (OS) is system software that manages computer hardware and software resources and provides common services for computer programs.

The operating system is a component of the system software in a computer system.

Application programs usually require an operating system to function.

Time-sharing operating systems schedule tasks for efficient use of the system and may also include accounting software for cost allocation of processor time, mass storage, printing, and other resources.

For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between programs and the computer hardware, although the application code is usually executed directly by the hardware and frequently makes system calls to an OS function or is interrupted by it.

Operating systems are found on many devices that contain a computer—from cellular phones and video game consoles to web servers and supercomputers.

Examples of popular modern operating systems include BlackBerry, BSD, iOS, Linux (Android, Chrome OS, Debian, Steam OS, Fedora, Gentoo, PCLinuxOS, RHEL), OS X, QNX, Microsoft Windows (and variant Windows Phone), and z/OS.

The first seven of these examples share roots in Unix.

Popular hard real-time operating systems include FreeRTOS, Micrium and VxWorks.


Kernel (operating system)   3/21/2016

Wikipedia

The kernel is a computer program that constitutes the central core of a computer's operating system.

It has complete control over everything that occurs in the system.

As such, it is the first program loaded on startup, and then manages the remainder of the startup, as well as input/output requests from software, translating them into data processing instructions for the central processing unit.

It is also responsible for managing memory, and for managing and communicating with computing peripherals, like printers, speakers, etc.

The kernel is a fundamental part of a modern computer's operating system.

A kernel connects the application software to the hardware of a computer

The critical code of the kernel is usually loaded into a protected area of memory, which prevents it from being overwritten by other, less frequently used parts of the operating system or by applications.

The kernel performs its tasks, such as executing processes and handling interrupts, in kernel space, whereas everything a user normally does, such as writing text in a text editor or running programs in a GUI (graphical user interface), is done in user space.

This separation prevents user data and kernel data from interfering with each other and thereby diminishing performance or causing the system to become unstable (and possibly crashing).

When a process makes requests of the kernel, the request is called a system call.

Various kernel designs differ in how they manage system calls and resources.

For example, a monolithic kernel executes all the operating system instructions in the same address space in order to improve the performance of the system.

A microkernel runs most of the operating system's background processes in user space, to make the operating system more modular and, therefore, easier to maintain.

The kernel's interface is a low-level abstraction layer.

Microkernel   3/21/2016

Wikipedia

In computer science, a microkernel (also known as µ-kernel) is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system (OS).

These mechanisms include low-level address space management, thread management, and inter-process communication (IPC).

If the hardware provides multiple rings or CPU modes, the microkernel may be the only software executing at the most privileged level, which is generally referred to as supervisor or kernel mode.

Traditional operating system functions, such as device drivers, protocol stacks and file systems, are typically removed from the microkernel itself and are instead run in user space.

In terms of the source code size, as a general rule microkernels tend to be smaller than monolithic kernels, usually sizing at under 10,000 lines of code.

The MINIX 3 microkernel, for example, has fewer than 6,000 lines of code.


Android   4/25/2016    Android Developer

Android Developer

The Android Operating System and Applications

Android is a mobile operating system (OS) currently developed by Google, based on the Linux kernel and designed primarily for touchscreen mobile devices such as smartphones and tablets.

Android's user interface is mainly based on direct manipulation, using touch gestures that loosely correspond to real-world actions, such as swiping, tapping and pinching, to manipulate on-screen objects, along with a virtual keyboard for text input.

In addition to touchscreen devices, Google has further developed Android TV for televisions, Android Auto for cars, and Android Wear for wrist watches, each with a specialized user interface.

Variants of Android are also used on notebooks, game consoles, digital cameras, and other electronics.

As of 2015, Android has the largest installed base of all operating systems.

Initially developed by Android, Inc., which Google bought in 2005, Android was unveiled in 2007, along with the founding of the Open Handset Alliance – a consortium of hardware, software, and telecommunication companies devoted to advancing open standards for mobile devices.

As of July 2013, the Google Play store has had over one million Android applications ("apps") published, and over 50 billion applications downloaded.

An April–November 2913 survey of mobile application developers found that 71% of developers create applications for Android and a 2015 survey found that 40% of full-time professional developers see Android as their priority target platform, which is comparable to Apple's iOS on 37% with both platforms far above others.

At Google I/O 2014, the company revealed that there were over one billion active monthly Android users, up from 538 million in November 2913.

Android's source code is released by Google under open source licenses, although most Android devices ultimately ship with a combination of open source and proprietary software, including proprietary software required for accessing Google services.

Android is popular with technology companies that require a ready-made, low-cost and customizable operating system for high-tech devices.

Its open nature has encouraged a large community of developers and enthusiasts to use the open-source code as a foundation for community-driven projects, which add new features for advanced users or bring Android to devices originally shipped with other operating systems.

At the same time, as Android has no centralized update system most Android devices fail to receive security updates: research in 2015 concluded that almost 90% of Android phones in use had known but unpatched security vulnerabilities due to lack of updates and support.

The success of Android has made it a target for patent litigation as part of the so-called "smartphone wars" between technology companies.

Android Developer

Apple OSX   4/25/2016

History of Mac OS

More than ever, Mac is the computer people love to use.

And one of the biggest reasons is OS X.

It’s what makes a Mac a Mac. OS X El Capitan, named for the iconic landmark in Yosemite National Park, builds on the groundbreaking features and beautiful design introduced in OS X Yosemite, refining the experience and improving performance in lots of little ways that make a big difference.

And it’s free to upgrade.

iOS 9   4/25/2016    Developing for iOS 9

iOS 9

Flashback - History of iOS (iPhone OS to iOS 8)

iOS (originally iPhone OS) is a mobile operating system created and developed by Apple Inc. and distributed exclusively for Apple hardware.

It is the operating system that presently powers many of the company's mobile devices, including the iPhone, iPad, and iPod touch.

In October 2015, it was the most commonly used mobile operating system, in a few countries, such as in Canada, the United States – but no longer in the North American continent as a whole, for smartphones – the United Kingdom, Norway, Sweden, Denmark, Japan, and Australia, while iOS is far behind Google's Android globally; iOS had a 19.7% share of the smartphone mobile operating system units shipped in the fourth quarter of 2014, behind Android with 76.6%.

However, on tablets, iOS is the most commonly used tablet operating system in the world, while it has lost majority in many countries (e. g. the Africa continent and briefly lost Asia).

Originally unveiled in 2007, for the iPhone, it has been extended to support other Apple devices such as the iPod Touch (September 2007), iPad (January 2010), iPad Mini (November 2012) and second-generation Apple TV onward (September 2010).

As of January 2015, Apple's App Store contained more than 1.4 million iOS applications, 725,000 of which are native for iPads.

These mobile apps have collectively been downloaded more than 100 billion times.

The iOS user interface is based on the concept of direct manipulation, using multi-touch gestures.

Interface control elements consist of sliders, switches, and buttons.

Interaction with the OS includes gestures such as swipe, tap, pinch, and reverse pinch, all of which have specific definitions within the context of the iOS operating system and its multi-touch interface.

Internal accelerometers are used by some applications to respond to shaking the device (one common result is the undo command) or rotating it in three dimensions (one common result is switching from portrait to landscape mode).

iOS shares with OS X some frameworks such as Core Foundation and Foundation Kit; however, its UI toolkit is Cocoa Touch rather than OS X's Cocoa, so that it provides the UIKit framework rather than the AppKit framework.

It is therefore not compatible with OS X for applications.

Also while iOS also shares the Darwin foundation with OS X, Unix-like shell access is not available for users and restricted for apps, making iOS not fully Unix-compatible either.

Major versions of iOS are released annually.

The current release, iOS 9.2, was released on December 8, 2015.

In iOS, there are four abstraction layers: the Core OS layer, the Core Services layer, the Media layer, and the Cocoa Touch layer.

The current version of the operating system (iOS 9), dedicates around 1.3 GB of the device's flash memory for iOS itself.

It runs on the iPhone 4S and later, iPad 2 and later, iPad Pro, all models of the iPad Mini, and the 5th-generation iPod Touch and later.

Linux   4/25/2016

Linux

Introduction to Linux

Linux is a Unix-like and mostly POSIX-compliant computer operating system (OS) assembled under the model of free and open-source software development and distribution.

The defining component of Linux is the Linux kernel, an operating system kernel first released on 5 October 1991 by Linus Torvalds.

The Free Software Foundation uses the name GNU/Linux to describe the operating system, which has led to some controversy.

Linux was originally developed as a free operating system for personal computers based on the Intel x86 architecture, but has since been ported to more computer hardware platforms than any other operating system.

Thanks to its dominance on smartphones, Android, which is built on top of the Linux kernel, has the largest installed base of all general-purpose operating systems.

Linux, in its original form, is also the leading operating system on servers and other big iron systems such as mainframe computers and virtually all fastest supercomputers, but is used on only around 1.6% of desktop computers with Linux-based Chrome OS taking about 5% of the overall and nearly 20% of the sub-$300 notebook sales.

Linux also runs on embedded systems, which are devices whose operating system is typically built into the firmware and is highly tailored to the system; this includes smartphones and tablet computers running Android and other Linux derivatives, TiVo and similar DVR devices, network routers, facility automation controls, televisions, video game consoles, and smartwatches.

The development of Linux is one of the most prominent examples of free and open-source software collaboration.

The underlying source code may be used, modified and distributed – commercially or non-commercially – by anyone under the terms of its respective licenses, such as the GNU General Public License.

Typically, Linux is packaged in a form known as a Linux distribution, for both desktop and server use.

Some of the popular mainstream Linux distributions are Debian, Ubuntu, Linux Mint, Fedora, openSUSE, Arch Linux and Gentoo, together with commercial Red Hat Enterprise Linux and SUSE Linux Enterprise Server distributions.

Linux distributions include the Linux kernel, supporting utilities and libraries, and usually a large amount of application software to fulfill the distribution's intended use.

Distributions oriented toward desktop use typically include a windowing system, such as X11, Mir or a Wayland implementation, and an accompanying desktop environment, such as GNOME or the KDE Software Compilation; some distributions may also include a less resource-intensive desktop, such as LXDE or Xfce.

Distributions intended to run on servers may omit all graphical environments from the standard install, and instead include other software to set up and operate a solution stack such as LAMP.

Because Linux is freely redistributable, anyone may create a distribution for any intended use.

Linux

Microsoft Windows   4/25/2016

Microsoft Windows

History Of Microsoft Windows And it's Evolution

Microsoft Windows (or simply Windows) is a metafamily of graphical operating systems developed, marketed, and sold by Microsoft.

It consists of several families of operating systems, each of which cater to a certain sector of the computing industry.

Active Windows families include Windows NT, Windows Embedded and Windows Phone; these may encompass subfamilies, e.g. Windows Embedded Compact (Windows CE) or Windows Server.

Defunct Windows families include Windows 9x and Windows Mobile.

Microsoft introduced an operating environment named Windows on November 20, 1985, as a graphical operating system shell for MS-DOS in response to the growing interest in graphical user interfaces (GUIs).

Microsoft Windows came to dominate the world's personal computer market with over 90% market share, overtaking Mac OS, which had been introduced in 1984.

However, since 2012, thanks to the massive growth of smartphones, Windows sells less than Android, which became the most popular operating system in 2014, when counting all of the computing platforms each operating system runs on; in 2014, the number of Windows devices sold were less than 25% of Android devices sold.

However, comparisons across different markets are not fully relevant; and for personal computers, Windows is still the most popular operating system.

As of July 2015, the most recent version of Windows for personal computers, tablets and smartphones is Windows 10.

The most recent versions for server computers and embedded devices are respectively Windows Server 2012 R2 and Windows Embedded 8.

A specialized version of Windows runs on the Xbox One game console.

The next server version of Windows is Windows Server 2016, which is expected to be released in early 2016.

Microsoft Windows

UNIX   4/25/2016

UNIX

AT&T Archives: The UNIX Operating System

The history of Unix dates back to the mid-1960s when the Massachusetts Institute of Technology, AT&T Bell Labs, and General Electric were jointly developing an experimental time sharing operating system called Multics for the GE-645 mainframe.

Multics introduced many innovations, but had many problems.

Bell Labs, frustrated by the size and complexity of Multics but not the aims, slowly pulled out of the project.

Their last researchers to leave Multics, Ken Thompson, Dennis Ritchie, Doug McIlroy, and Joe Ossanna, decided to redo the work on a much smaller scale.

In 1979, Dennis Ritchie described their vision for Unix:

What we wanted to preserve was not just a good environment in which to do programming, but a system around which a fellowship could form.

We knew from experience that the essence of communal computing, as supplied by remote-access, time-shared machines, is not just to type programs into a terminal instead of a keypunch, but to encourage close communication.

UNIX

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