What is Operating System? Types of OS, Features and Examples

What is an Operating System?

An Operating System (OS) is a software that acts as an interface between computer hardware components and the user. Every computer system must have at least one operating system to run other programs. Applications like Browsers, MS Office, Notepad Games, etc., need some environment to run and perform its tasks.

The OS helps you to communicate with the computer without knowing how to speak the computer’s language. It is not possible for the user to use any computer or mobile device without having an operating system. Introduction to Operating System

History Of OS

• Operating systems were first developed in the late 1950s to manage tape storage
• The General Motors Research Lab implemented the first OS in the early 1950s for their IBM 701
• In the mid-1960s, operating systems started to use disks
• In the late 1960s, the first version of the Unix OS was developed
• The first OS built by Microsoft was DOS. It was built in 1981 by purchasing the 86-DOS software from a Seattle company
• The present-day popular OS Windows first came to existence in 1985 when a GUI was created and paired with MS-DOS.

Examples of Operating System with Market Share

Following are the examples of Operating System with the latest Market Share

OS Name	Share
Windows	40.34
Android	37.95
iOS	15.44
Mac OS	4.34
Linux	0.95
Chrome OS	0.14
Windows Phone OS	0.06

Types of Operating System (OS)

Following are the popular types of Operating System:

• Batch Operating System
• Multitasking/Time Sharing OS
• Multiprocessing OS
• Real Time OS
• Distributed OS
• Network OS
• Mobile OS

Batch Operating System

Some computer processes are very lengthy and time-consuming. To speed the same process, a job with a similar type of needs are batched together and run as a group.

The user of a batch operating system never directly interacts with the computer. In this type of OS, every user prepares his or her job on an offline device like a punch card and submit it to the computer operator.

Multi-Tasking/Time-sharing Operating systems

Time-sharing operating system enables people located at a different terminal(shell) to use a single computer system at the same time. The processor time (CPU) which is shared among multiple users is termed as time sharing.

Real time OS

A real time operating system time interval to process and respond to inputs is very small. Examples: Military Software Systems, Space Software Systems are the Real time OS example.

Distributed Operating System

Distributed systems use many processors located in different machines to provide very fast computation to its users.

Network Operating System

Network Operating System runs on a server. It provides the capability to serve to manage data, user, groups, security, application, and other networking functions.

Mobile OS

Mobile operating systems are those OS which is especially that are designed to power smartphones, tablets, and wearables devices.

Some most famous mobile operating systems are Android and iOS, but others include BlackBerry, Web, and watchOS.

Functions of Operating System

Below are the main functions of Operating System: Functions of Operating System

In an operating system software performs each of the function:

1. Process management:- Process management helps OS to create and delete processes. It also provides mechanisms for synchronization and communication among processes.

1. Memory management:- Memory management module performs the task of allocation and de-allocation of memory space to programs in need of this resources.

1. File management:- It manages all the file-related activities such as organization storage, retrieval, naming, sharing, and protection of files.

1. Device Management: Device management keeps tracks of all devices. This module also responsible for this task is known as the I/O controller. It also performs the task of allocation and de-allocation of the devices.

1. I/O System Management: One of the main objects of any OS is to hide the peculiarities of that hardware devices from the user.

1. Secondary-Storage Management: Systems have several levels of storage which includes primary storage, secondary storage, and cache storage. Instructions and data must be stored in primary storage or cache so that a running program can reference it.

1. Security:- Security module protects the data and information of a computer system against malware threat and authorized access.

1. Command interpretation: This module is interpreting commands given by the and acting system resources to process that commands.

1. Networking: A distributed system is a group of processors which do not share memory, hardware devices, or a clock. The processors communicate with one another through the network.

1. Job accounting: Keeping track of time & resource used by various job and users.

1. Communication management: Coordination and assignment of compilers, interpreters, and another software resource of the various users of the computer systems.

Features of Operating System (OS)

Here is a list important features of OS:

• Protected and supervisor mode
• Allows disk access and file systems Device drivers Networking Security
• Program Execution
• Memory management Virtual Memory Multitasking
• Handling I/O operations
• Manipulation of the file system
• Error Detection and handling
• Resource allocation
• Information and Resource Protection

Advantage of using Operating System

• Allows you to hide details of hardware by creating an abstraction
• Easy to use with a GUI
• Offers an environment in which a user may execute programs/applications
• The operating system must make sure that the computer system convenient to use
• Operating System acts as an intermediary among applications and the hardware components
• It provides the computer system resources with easy to use format
• Acts as an intermediator between all hardware’s and software’s of the system

Disadvantages of using Operating System

• If any issue occurs in OS, you may lose all the contents which have been stored in your system
• Operating system’s software is quite expensive for small size organization which adds burden on them. Example Windows
• It is never entirely secure as a threat can occur at any time

What is a Kernel?

The kernel is the central component of a computer operating systems. The only job performed by the kernel is to the manage the communication between the software and the hardware. A Kernel is at the nucleus of a computer. It makes the communication between the hardware and software possible. While the Kernel is the innermost part of an operating system, a shell is the outermost one.

Features of Kennel

• Low-level scheduling of processes
• Inter-process communication
• Process synchronization
• Context switching

Types of Kernels

There are many types of kernels that exists, but among them, the two most popular kernels are:

1.Monolithic

A monolithic kernel is a single code or block of the program. It provides all the required services offered by the operating system. It is a simplistic design which creates a distinct communication layer between the hardware and software.

2. Microkernels

Microkernel manages all system resources. In this type of kernel, services are implemented in different address space. The user services are stored in user address space, and kernel services are stored under kernel address space. So, it helps to reduce the size of both the kernel and operating system.

Is there an equivalent of ‘which’ on the Windows command line?

As I sometimes have path problems, where one of my own cmd scripts is hidden (shadowed) by another program (earlier on the path), I would like to be able to find the full path to a program on the Windows command line, given just its name.

Is there an equivalent to the UNIX command ‘which’?

On UNIX, which command prints the full path of the given command to easily find and repair these shadowing problems.

26 Answers 26

Windows Server 2003 and later (i.e. anything after Windows XP 32 bit) provide the where.exe program which does some of what which does, though it matches all types of files, not just executable commands. (It does not match built-in shell commands like cd .) It will even accept wildcards, so where nt* finds all files in your %PATH% and current directory whose names start with nt .

Try where /? for help.

Note that Windows PowerShell defines where as an alias for the Where-Object cmdlet, so if you want where.exe , you need to type the full name instead of omitting the .exe extension.

While later versions of Windows have a where command, you can also do this with Windows XP by using the environment variable modifiers, as follows:

You don’t need any extra tools and it’s not limited to PATH since you can substitute any environment variable (in the path format, of course) that you wish to use.

And, if you want one that can handle all the extensions in PATHEXT (as Windows itself does), this one does the trick:

It actually returns all possibilities but you can tweak it quite easily for specific search rules.

$PATH:%i To add it to an alias.bat script that you load everytime you run cmd.exe (put the above script in a new directory called C:\usr\aliases): DOSKEY which=C:\usr\aliases\which.bat $* Then you can make a script to launch cmd.exe with the alias.bat file: cmd.exe /K E:\usr\aliases\alias.bat – Brad T. Apr 25 ’14 at 20:42

Under PowerShell, Get-Command will find executables anywhere in $Env:PATH .

And since powershell let’s you define aliases, which can be defined like so.

PowerShell commands are not just executable files ( .exe , .ps1 , etc). They can also be cmdlets, functions, aliases, custom executable suffixes set in $Env:PATHEXT , etc. Get-Command is able to find and list all of these commands (quite akin to Bash’s type -a foo ). This alone makes it better than where.exe , which.exe , etc which are typically limited to finding just executables.

Finding executables using only part of the name

Finding custom executables

Unlike UNIX, where executables are files with the executable ( +x ) bit set, executables on windows are files present in one of the directories specified in the $PATH env. variable whose filename suffixes are named in the $PATHEXT env. variable (defaults to .COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC;.CPL ).

As Get-Command also honours this env. variable, it can be extended to list custom executables. e.g.

See Get-Command for more options and examples.

In Windows PowerShell:

If you have PowerShell installed (which I recommend), you can use the following command as a rough equivalent (substitute programName for your executable’s name):

The GnuWin32 tools have which , along with a whole slew of other Unix tools.

In Windows CMD which calls where :

Cygwin is a solution. If you don’t mind using a third-party solution, then Cygwin is the way to go.

Cygwin gives you the comfort of *nix in the Windows environment (and you can use it in your Windows command shell, or use a *nix shell of your choice). It gives you a whole host of *nix commands (like which ) for Windows, and you can just include that directory in your PATH .

In PowerShell, it is gcm , which gives formatted information about other commands. If you want to retrieve only path to executable, use .Source .

For instance: gcm git or (gcm git).Source

• Available for Windows XP.
• Available since PowerShell 1.0.
• gcm is an alias of Get-Command cmdlet.
• Without any parameters, it lists down all the available commands offered by the host shell.
• You can create a custom alias with Set-Alias which gcm and use it like: (which git).Source .
• Official docs: https://technet.microsoft.com/en-us/library/ee176842.aspx

I have a function in my PowerShell profile named ‘which’

Here’s what the output looks like:

gold on windows platforms, puts all the nice unix utilities on a standard windows DOS. Been using it for years.

It has a ‘which’ included. Note that it’s case sensitive though.

NB: to install it explode the zip somewhere and add . \UnxUtils\usr\local\wbin\ to your system path env variable.

If you can find a free Pascal compiler, you can compile this. At least it works and shows the algorithm necessary.

Not in stock Windows but it is provided by Services for Unix and there are several simple batch scripts floating around that accomplish the same thing such this this one.

The best version of this I’ve found on Windows is Joseph Newcomer’s «whereis» utility, which is available (with source) from his site.

The article about the development of «whereis» is worth reading.

None of the Win32 ports of Unix which that I could find on the Internet are satistactory, because they all have one or more of these shortcomings:

• No support for Windows PATHEXT variable. (Which defines the list of extensions implicitely added to each command before scanning the path, and in which order.) (I use a lot of tcl scripts, and no publicly available which tool could find them.)
• No support for cmd.exe code pages, which makes them display paths with non-ascii characters incorrectly. (I’m very sensitive to that, with the ç in my first name :-))
• No support for the distinct search rules in cmd.exe and the PowerShell command line. (No publicly available tool will find .ps1 scripts in a PowerShell window, but not in a cmd window!)

So I eventually wrote my own which, that suports all the above correctly.