An operating system (OS) manages application programs and hardware devices. It determines which applications run and in what order, manages memory sharing between applications, and handles input/output to hardware. Popular desktop OSs include Windows, Mac OS, and Linux. Batch systems run jobs non-interactively while time-sharing systems allow interactive use by multiple users simultaneously. Distributed, network, real-time, and embedded OSs are designed for specialized environments. A library OS provides typical OS services as libraries to compose with applications.

2. Operating System (OS)
• An operating system (OS) is the program that, after
being initially loaded into the computer by
a boot program, manages all the other programs in a
computer.
• The other programs are called applications or
application programs.
• The application programs make use of the operating
system by making requests for services through a
defined application program interface (API).
• In addition, users can interact directly with the
operating system through a user interface such as a
command line or a graphical user interface (GUI).

4. Various services for
applications
• In a multitasking operating system where multiple programs
can be running at the same time, the operating system
determines which applications should run in what order and
how much time should be allowed for each application
before giving another application a turn.
• It manages the sharing of internal memory among multiple
applications.
• It handles input and output to and from attached hardware
devices, such as hard disks, printers, and dial-up ports.

5. Various services for
applications
• It sends messages to each application or interactive
user (or to a system operator) about the status of
operation and any errors that may have occurred.
• It can offload the management of what are
called batch jobs (for example, printing) so that the
initiating application is freed from this work.
• On computers that can provide parallel processing,
an operating system can manage how to divide the
program so that it runs on more than one processor
at a time.

6. Classification of Operating
systems
• Multi-user: Allows two or more users to run programs at the
same time. Some operating systems permit hundreds or even
thousands of concurrent users.
• Multiprocessing: Supports running a program on more than
one CPU.
• Multitasking : Allows more than one program to run
concurrently.
• Multithreading : Allows different parts of a single program to
run concurrently.
• Real time: Responds to input instantly. General-purpose
operating systems, such as DOSand UNIX, are not real-time.

7. Most Popular Desktop
Operating Systems
• The three most popular types of operating systems for
personal and business computing include Linux,
Windows and Mac.
• Windows
• Microsoft Windows is a family of operating systems for
personal and business computers. Windows dominates
the personal computer world, offering a graphical user
interface (GUI), virtual memory management,
multitasking, and support for many peripheral devices.

8. Most Popular Desktop
Operating Systems
• Mac:
• Mac OS is the official name of the Apple Macintosh
operating system. Mac OS features a graphical user
interface (GUI) that utilizes windows, icons, and all
applications that run on a Macintosh computer have a
similar user interface.
• Linux:
• Linux is a freely distributed open source operating
system that runs on a number of hardware platforms.
The Linux kernel was developed mainly by Linus
Torvalds and it is based on Unix.

11. Batch operating system
• The users of a batch operating system do not interact with
the computer directly. Each user prepares his job on an off-
line device like punch cards and submits it to the computer
operator. To speed up processing, jobs with similar needs
are batched together and run as a group. The programmers
leave their programs with the operator and the operator
then sorts the programs with similar requirements into
batches.
• The problems with Batch Systems are as follows −
• Lack of interaction between the user and the job.
• CPU is often idle, because the speed of the mechanical I/O
devices is slower than the CPU.
• Difficult to provide the desired priority.

12. Time-sharing operating
systems
• Time-sharing is a technique which enables many
people, located at various terminals, to use a particular
computer system at the same time. Time-sharing or
multitasking is a logical extension of
multiprogramming. Processor's time which is shared
among multiple users simultaneously is termed as
time-sharing.
• The main difference between Multiprogrammed Batch
Systems and Time-Sharing Systems is that in case of
Multiprogrammed batch systems, the objective is to
maximize processor use, whereas in Time-Sharing
Systems, the objective is to minimize response time.

13. Time-sharing operating
systems
• Advantages of Timesharing operating systems are
as follows −
• Provides the advantage of quick response.
• Avoids duplication of software.
• Reduces CPU idle time.
• Disadvantages of Time-sharing operating systems
are as follows −
• Problem of reliability.
• Question of security and integrity of user
programs and data.
• Problem of data communication.

14. Distributed operating
System
• Distributed systems use multiple central processors to serve multiple real-
time applications and multiple users. Data processing jobs are distributed
among the processors accordingly.
• The processors communicate with one another through various
communication lines (such as high-speed buses or telephone lines). The
advantages of distributed systems are as follows −
• With resource sharing facility, a user at one site may be able to use the
resources available at another.
• Speedup the exchange of data with one another via electronic mail.
• If one site fails in a distributed system, the remaining sites can potentially
continue operating.
• Better service to the customers.
• Reduction of the load on the host computer.
• Reduction of delays in data processing.

15. Network operating System
• A Network Operating System runs on a server and
provides the server the capability to manage data,
users, groups, security, applications, and other
networking functions. The primary purpose of the
network operating system is to allow shared file and
printer access among multiple computers in a network,
typically a local area network (LAN), a private network
or to other networks.
• Examples of network operating systems include
Microsoft Windows Server 2003, Microsoft Windows
Server 2008, UNIX, Linux, Mac OS X, Novell NetWare,
and BSD.

16. Network operating System
• The advantages of network operating systems are as follows −
• Centralized servers are highly stable.
• Security is server managed.
• Upgrades to new technologies and hardware can be easily
integrated into the system.
• Remote access to servers is possible from different locations and
types of systems.
• The disadvantages of network operating systems are as follows −
• High cost of buying and running a server.
• Dependency on a central location for most operations.
• Regular maintenance and updates are required.

17. Real Time operating System
• A real-time system is defined as a data processing system in which
the time interval required to process and respond to inputs is so
small that it controls the environment. The time taken by the
system to respond to an input and display of required updated
information is termed as the response time. So in this method, the
response time is very less as compared to online processing.
• Real-time systems are used when there are rigid time requirements
on the operation of a processor or the flow of data and real-time
systems can be used as a control device in a dedicated application.
A real-time operating system must have well-defined, fixed time
constraints, otherwise the system will fail. For example, Scientific
experiments, medical imaging systems, industrial control systems,
weapon systems, robots, air traffic control systems, etc.

18. Real Time operating System
• There are two types of real-time operating systems.
• Hard real-time systems
• Hard real-time systems guarantee that critical tasks
complete on time. In hard real-time systems, secondary
storage is limited or missing and the data is stored in ROM.
In these systems, virtual memory is almost never found.
• Soft real-time systems
• Soft real-time systems are less restrictive. A critical real-
time task gets priority over other tasks and retains the
priority until it completes. Soft real-time systems have
limited utility than hard real-time systems. For example,
multimedia, virtual reality, Advanced Scientific Projects like
undersea exploration and planetary rovers, etc.

19. Embedded operating system
• Embedded operating system are designed to be
used in embedded computer system.
• They are designed to operate on small machines like
PDAs with less autonomy.
• They are able to operate with a limited number of
resources. They are very compact and extremely
efficient by design.
• Windows CE and Minix 3 are some examples of
embedded operating systems.

20. Embedded operating system
• The hardware running an embedded operating
system can be very limited in resources such
as RAM and ROM, therefore embedded design of
these operating systems may have a narrow
scope tailored to a specific application in order to
achieve desired operation under these
constraints.
• In order to take better advantage of the
processing power of the CPU, software
developers may write critical code directly
in assembly.

21. Library Operating System
• A library operating system is one in which the
services that a typical operating system
provides, such as networking, are provided in
the form of libraries and composed with the
application and configuration code to
construct a unikernel: a specialized, single
address space, machine image that can be
deployed to cloud or embedded
environments.