The document discusses operating systems and their functions. It begins by defining an operating system as system software that manages computer hardware and resources, providing services to programs. It then discusses the dominant desktop, mobile, and server operating systems. Finally, it lists and describes several key functions of operating systems, including I/O management, memory management, process management, time sharing, security, deadlock prevention, and interrupt handling.

2. INTRODUCTION
An operating system (OS) is system software that
manages computer hardware and software resources and provides
common services for computer programs.
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,[1][2] 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.

3. The dominant desktop operating system is Microsoft
Windows with a market share of around
82.74%. macOS by Apple Inc. is in second place (13.23%),
and the varieties of Linux are collectively in third place
(1.57%).[3] In the mobile (smartphone and tabletcombined)
sector, use in 2017 is up to 70% of Google's Android[4] and
according to third quarter 2016 data, Android on
smartphones is dominant with 87.5 percent and a growth
rate 10.3 percent per year, followed by Apple's iOS with
12.1 percent and a per year decrease in market share of 5.2
percent, while other operating systems amount to just 0.3
percent.[5] Linux distributions are dominant in the server
and supercomputing sectors. Other specialized classes of
operating systems, such as embedded and real-time
systems, exist for many applications.

5. FUNCTIONS OF OPERATING
SYSTEM
There are Many Functions those are Performed by the
Operating System But the Main Goal of Operating System is
to Provide the Interface between the user and the hardware
Means Provides the Interface for Working on the System by
the user. The various Functions those are Performed by the
Operating System are-
 I/O Management: OS manages I/O devices and makes the
I/O process effective. OS accepts the input from the input
device, stores it in the main memory, ask the CPU to
process it and finally provides the result to the output
devices for output.

6.  Command Interpreter: Command interpreter is one of the
part of operating system which reads the commands that
user types in at a terminal, interprets them and translate
them into a detailed set of instructions that the computer
hardware can understand. It varies widely from one OS to
other OS. Every OS must provide command interpreter for
its operation.
 Memory Management: Memory is the large array of words
or bytes, each with its own address. When user requests
CPU for read/write operation, OS determines the amount of
memory required for the program instructions and data.
Then, OS allocates required memory to load the program
and data into RAM. When program terminates its memory
area is free and the same memory area is allocated for
other programs.

7.  Process Management: OS finds the status of processor
and processes, chooses a job, chooses processer in the
job, allocates the processor to the process and frees the
processer when the process is executed.
 Time Sharing: OS manages the time of CPU. The kernel
OS checks frequency for other processes requesting CPU
time. Time sharing checks for CPU request from higher
priority processes that are made every 10 milliseconds.
When two or more processes at the same priority level are
competing for the CPU time, CPU time is sliced into
segments, defined by time slice and passed from process to
process in a round robin fashion, preventing a single
process from monopolizing the CPU until it blocks or
terminates.

8.  Security: OS makes sure that only authorized users get
access to the computer and its data and the users only do
things they are authorized to do.
 Deadlock Prevention: During processing, a situation can
arise in which a resource shared by two or more processes
cannot continue because the resource required by one
process is held by the other. This situation is called
deadlock. OS ensures that the above condition do not hold
by carefully allocating resources.
 Interrupt Handling: Interrupt is a signal generated from a
device or program when they need attention of the CPU. OS
determines the type of interrupt and priority of the interrupt,
stops the execution process of CPU, preserves the initial
state of the CPU, perform the requested operation and
brings the CPU at the same state when it was stopped.