The operating system is the most important program that runs on a computer. Every general-purpose computer must have an operating system to run other programs. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers.

For large systems, the operating system has even greater responsibilities and powers. It is like a traffic cop — it makes sure different programs and users running at the same time do not interfere with each other. The operating system is also responsible for security, ensuring that unauthorized users do not access the system.


HISTORY OF OPERATING SYSTEMS

Historically operating systems have been tightly related to the computer architecture, it is good idea to study the history of operating systems from the architecture of the computers on which they run.

Operating systems have evolved through a number of distinct phases or generations which corresponds roughly to the decades.
THE 1940’S – FIRST GENERATIONS

The earliest electronic digital computers had no operating systems. Machines of the time were so primitive that programs were often entered one bit at time on rows of mechanical switches (plug boards). Programming languages were unknown (not even assembly languages). Operating systems were unheard of.
THE 1950’S – SECOND GENERATION

By the early 1950’s, the routine had improved somewhat with the introduction of punch cards. The General Motors Research Laboratories implemented the first operating systems in early 1950’s for their IBM 701. The system of the 50’s generally ran one job at a time. These were called single-stream batch processing systems because programs and data were submitted in groups or batches.
THE 1960’S – THIRD GENERATION

The systems of the 1960’s were also batch processing systems, but they were able to take better advantage of the computer’s resources by running several jobs at once. So operating systems designers developed the concept of multiprogramming in which several jobs are in main memory at once; a processor is switched from job to job as needed to keep several jobs advancing while keeping the peripheral devices in use.

For example, on the system with no multiprogramming, when the current job paused to wait for other I/O operation to complete, the CPU simply sat idle until the I/O finished. The solution for this problem that evolved was to partition memory into several pieces, with a different job in each partition. While one job was waiting for I/O to complete, another job could be using the CPU.

Another major feature in third-generation operating system was the technique called spooling (simultaneous peripheral operations on line). In spooling, a high-speed device like a disk interposed between a running program and a low-speed device involved with the program in input/output. Instead of writing directly to a printer, for example, outputs are written to the disk. Programs can run to completion faster, and other programs can be initiated sooner when the printer becomes available, the outputs may be printed.

Note that spooling technique is much like thread being spun to a spool so that it may be later be unwound as needed.

Another feature present in this generation was time-sharing technique, a variant of multiprogramming technique, in which each user has an on-line (i.e., directly connected) terminal. Because the user is present and interacting with the computer, the computer system must respond quickly to user requests, otherwise user productivity could suffer. Timesharing systems were developed to multi-program large number of simultaneous interactive users.
FOURTH GENERATION

With the development of LSI (Large Scale Integration) circuits, chips, operating system entered the personal computer and the workstation age. Microprocessor technology evolved to the point that it became possible to build desktop computers as powerful as the mainframes of the 1970s. Two operating systems have dominated the personal computer scene: MS-DOS, written by Microsoft, Inc. for the IBM PC and other machines using the Intel 8088 CPU and its successors, and UNIX, which is dominant on the large personal computers using the Motorola 6899 CPU family.


TYPES OF OPERATING SYSTEM
SINGLE USER, SINGLE TASKING OPERATING SYSTEM

This type of operating system only has to deal with one person at a time, running one user application at a time. An example of this kind of operating system would be found on a mobile phone. There can only be one user using the mobile and that person is only using one of its applications at a time.
SINGLE USER, MULTI TASKING OPERATING SYSTEM

You will find this kind of operating system on a personal computer. The operating system is designed mainly with a single user in mind, but it can deal with many applications running at the same time. For example, you might be writing an essay, while searching the internet, downloading a video file and also listening to a piece of music.
MULTI TASKING OPERATING SYSTEM

A multitasking operating system is any type of operating system that is capable of running more than one program at a time. Most modern operating systems are configured to handle multiple programs simultaneously, with the exception of some privately developed systems that are designed for use in specific business settings. With older examples of the multitasking operating system, managing two or more tasks normally involved switching system resources back and forth between the two running processes. The system would execute tasks for one, freeze that program for a few seconds, and then execute tasks for the other program. While this approach did create a short time lag for the operator, this lag was usually no more than a few seconds and still offered considerable more efficiency than the older single-task operating system.
MULTI USER OPERATING SYSTEM

A multi-user operating system allows many different users to take advantage of the computer’s resources simultaneously. The operating system must make sure that the requirements of the various users are balanced, and that each of the programs they are using has sufficient and separate resources so that a problem with one user doesn’t affect the entire community of users. UNIX, VMS and mainframe operating systems, such as MVS, are examples of multi-user operating systems.
DISTRIBUTED OPERATING SYSTEM

Distributed Operating System is a model where distributed applications are running on multiple computers linked by communications. A distributed operating system is an extension of the network operating system that supports higher levels of communication and integration of the machines on the network. This system looks to its users like an ordinary centralized operating system but runs on multiple, independent central processing units (CPUs).
EMBEDDED OPERATING SYSTEM

An embedded operating system is a computer operating system that is part of a different kind of machine. Examples include computers in cars, traffic lights, digital televisions, ATMs, airplane controls, point of sale (POS) terminals, digital cameras, GPS navigation systems, elevators, digital media receivers and smart meters, among many other possibilities. In contrast to an operating system for a general-purpose computer, an embedded operating system is typically quite limited in terms of function – depending on the device in question, the system may only run a single application. However, that single application is crucial to the device’s operation, so an embedded OS must be reliable and able to run with constraints on memory, size and processing power.
REAL TIME OPERATING SYSTEM

A real-time operating system (RTOS) is an operating system (OS) intended to serve real-time application process data as it comes in, typically without buffering delays. Processing time requirements (including any OS delay) are measured in tenths of seconds or shorter. A key characteristic of an RTOS is the level of its consistency concerning the amount of time it takes to accept and complete an application’s task; the variability is jitter. A hard real-time operating system has less jitter than a soft real-time operating system. The chief design goal is not high throughput, but rather a guarantee of a soft or hard performance category. An RTOS that can usually or generally meet a deadline is a soft real-time OS, but if it can meet a deadline deterministically it is a hard real-time OS.


MAJOR OPERATING SYSTEMS
MICROSOFT WINDOWS

Microsoft Windows (or simply Windows) is a meta-family 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, it sells less than Android, that became the most popular operating system in 2014, when counting on all of the computing platforms Windows runs on (same as Android), not just desktop; in 2014, selling less than a quarter of Android.

As of April 2014, the most recent versions of Windows for personal computers, smartphones, server computers and embedded devices are respectively Windows 8.1, Windows Phone 8.1, Windows Server 2012 R2 and Windows Embedded 8. A specialized version of Windows runs on the Xbox One game console.

The next version of Windows is Windows 10 and is currently available as a technical preview; it is set for release for phones, tablets, laptops, and PCs in late 2015.
MAC OS

Mac OS is a series of graphical user interface-based operating systems developed by Apple Inc. for their Macintosh line of computer systems.

The original operating system was first introduced in 1984 as being integral to the original Macintosh, and referred to as the “System”. Referred to by its major revision starting with “System 6” and “System 7″, Apple rebranded version 7.6 as “Mac OS” as part of their Macintosh clone program in 1996. The Macintosh, specifically its system software, is credited with having popularized the early graphical user interface concept.

Macintosh operating systems have been released in two major series. Up to major revision 9, from 1984 to 2000, it is historically known as Classic Mac OS. Major revision 10, from 2001 to present, is branded OS X (originally referred to as Mac OS X). Major revisions to the Macintosh OS are now issued as point revisions, such that, for example, 10.2 is substantially different from 10.5. Both series share a general interface design, and there has been some overlap with shared application frameworks and virtual machine technology for compatibility; but the two series also have deeply different architectures.
LINUX

Linux is a Unix-like and mostly POSIX-compliant computer operating system 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 Intel x86–based personal computers, but has since been ported to more computer hardware platforms than any other operating system. It is the leading operating system on servers and other big iron systems such as mainframe computers and supercomputers, but is used on only around 1% of desktop computers. 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 mobile phones, tablet computers, network routers, facility automation controls, televisions and video game consoles. Android, the most widely used operating system for tablets and smartphones, is built on top of the Linux kernel.

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 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 popular mainstream Linux distributions include Debian, Ubuntu, Linux Mint, Fedora, openSUSE, Arch Linux, and the commercial Red Hat Enterprise Linux and SUSE Linux Enterprise Server. Linux distributions include the Linux kernel, supporting utilities and libraries and usually a large amount of application software to fulfil the distribution’s intended use.

A distribution oriented toward desktop use will typically include X11, Wayland or Mir as the windowing system, and an accompanying desktop environment such as GNOME or the KDE Software Compilation. Some such distributions may include a less resource intensive desktop such as LXDE or Xfce, for use on older or less powerful computers. A distribution intended to run as a server 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.


COMPONENTS OF OPERATING SYSTEMS

Even though, not all systems have the same structure many modern operating systems share the same goal of supporting the following types of system components.
PROCESS MANAGEMENT

The operating system manages many kinds of activities ranging from user programs to system programs like printer spooler, name servers, file server etc. Each of these activities is encapsulated in a process. A process includes the complete execution context (code, data, PC, registers, OS resources in use etc.).

It is important to note that a process is not a program. A process is only ONE instant of a program in execution. There are many processes can be running the same program. The five major activities of an operating system in regard to process management are:

Creation and deletion of user and system processes.
Suspension and resumption of processes.
A mechanism for process synchronization.
A mechanism for process communication.
A mechanism for deadlock handling.

MAIN-MEMORY MANAGEMENT

Primary-Memory or Main-Memory is a large array of words or bytes. Each word or byte has its own address. Main-memory provides storage that can be access directly by the CPU. That is to say for a program to be executed, it must be in the main memory.

The major activities of an operating in regard to memory-management are:

Keep track of which part of memory are currently being used and by whom.
Decide which processes are loaded into memory when memory space becomes available.
Allocate and de-allocate memory space as needed.

FILE MANAGEMENT

A file is a collected of related information defined by its creator. Computer can store files on the disk (secondary storage), which provide long term storage. Some examples of storage media are magnetic tape, magnetic disk and optical disk. Each of these media has its own properties like speed, capacity, and data transfer rate and access methods.

A file system is normally organized into directories to ease their use. These directories may contain files and other directories. The five main major activities of an operating system in regard to file management are:

The creation and deletion of files.
The creation and deletion of directions.
The support of primitives for manipulating files and directions.
The mapping of files onto secondary storage.
The backup of files on stable storage media.

I/O SYSTEM MANAGEMENT

I/O subsystem hides the peculiarities of specific hardware devices from the user. Only the device driver knows the peculiarities of the specific device to which it is assigned.
SECONDARY-STORAGE MANAGEMENT

Generally speaking, systems have several levels of storage, including primary storage, secondary storage and cache storage. Instructions and data must be placed in primary storage or cache to be referenced by a running program. Because main memory is too small to accommodate all data and programs, and its data are lost when power is lost, the computer system must provide secondary storage to back up main memory. Secondary storage consists of tapes, disks, and other media designed to hold information that will eventually be accessed in primary storage (primary, secondary, cache) is ordinarily divided into bytes or words consisting of a fixed number of bytes. Each location in storage has an address; the set of all addresses available to a program is called an address space.

The three major activities of an operating system in regard to secondary storage management are:
Managing the free space available on the secondary-storage device.
Allocation of storage space when new files have to be written.
Scheduling the requests for memory access.

NETWORKING

A distributed system is a collection of processors that do not share memory, peripheral devices, or a clock. The processors communicate with one another through communication lines called network. The communication-network design must consider routing and connection strategies, and the problems of contention and security.
PROTECTION SYSTEM

If a computer system has multiple users and allows the concurrent execution of multiple processes, then the various processes must be protected from one another’s activities. Protection refers to mechanism for controlling the access of programs, processes, or users to the resources defined by a computer system.
COMMAND INTERPRETER SYSTEM

A command interpreter is an interface of the operating system with the user. The user gives commands with are executed by operating system (usually by turning them into system calls). The main function of a command interpreter is to get and execute the next user specified command. Command-Interpreter is usually not part of the kernel, since multiple command interpreters (shell, in UNIX terminology) may be supported by an operating system, and they do not really need to run in kernel mode. There are two main advantages to separating the command interpreter from the kernel.

If we want to change the way the command interpreter looks, i.e., I want to change the interface of command interpreter, I am able to do that if the command interpreter is separate from the kernel. I cannot change the code of the kernel so I cannot modify the interface.

If the command interpreter is a part of the kernel it is possible for a malicious process to gain access to certain part of the kernel that it showed not have to avoid this ugly scenario it is advantageous to have the command interpreter separate from kernel.

Source: http://www.inyavic.com/2015/03/06/operating-system/

What is Operating System and It’s Types – Operating System this could be defined as an interface or link between the computer syste4m and the computer operator. Someone could also define operating system as a low level software which have a basic function to support the hardware which could be use to perform some schedule. http://www.techcules.com/operating-system-types/

Computer has been program to run with an operating system in other for your pc programs not to interfere with one another.

The operating system is the most important program that runs on a computer. Every general-purpose computer must have an operating system to run other programs and applications. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers.

For large systems, the operating system has even greater responsibilities and powers. It is like a traffic cop -- it makes sure that different programs and users running at the same time do not interfere with each other. The operating system is also responsible for security, ensuring that unauthorized users do not access the system.