The main use of Operating System is
1. to ensure that a computer can be used to extract what the user wants it do.
2. Easy interaction between the users and computers.
3. Starting computer operation automatically when power is turned on (Booting),
4. Controlling Input and Output Devices
5. Manage the utilization of main memory.
6. Providing security to user programs.

(i) Android is a mobile operating system developed by Google, based on the Linux and designed primarily for touchscreen mobile devices such as smartphones and tablets.
(ii) Google has further developed Android TV for televisions, Android Auto for cars and Android Wear for wrist watches, each with a specialized user interface.
(iii) Variants of Android are also used on game consoles, digital cameras, PCs and other electronic gadgets.

UNIX :
UNIX is a family of multitasking, multi-user operating systems that derive originally from AT&T Bell Labs, where the development began in the 1970s by Ken Thompson and Dennis Ritchie.
Linux
(i) Linux is a family of open-source operating systems. It can be modified and distributed by anyone around the world.
(ii) This is different from proprietary software like Windows, which can only be modified by the company that owns it.
(iii) The main advantage of the Linux operating system is that it is open source. There are many versions and their updates
(iv) Most of the servers run on Linux because it is easy to customize.

(a) FIFO (First In First Out)Scheduling :
(i) This algorithm is based on queuing technique. Assume that a student is standing in a queue (Row) to get grade sheet from his/her teacher.
(ii) The other student who stands first in the queue gets his/her grade sheet first and leaves from the queue (Row). Followed by the next student in the queue gets it corrected and so on. This is the basic logic of the FIFO algorithm.
(iii) Technically, the process that enters the queue first is executed first by the CPU, followed by the next and so on. The processes are executed in the order of the queue (row).
(b) SJF (Shortest Job First)Scheduling:
(i) This algorithm works based on the size of the job being executed by the CPU.
(ii) Consider two jobs A and B.
(iii) 1) A = 6 kilo bytes 2) B = 9 kilo bytes.
(iv) First the job "A" will be assigned and then job "B" gets its turn.
(c) Round Robin Scheduling :
(i) The Round Robin (RR) Scheduling algorithm is designed especially for time sharing systems.
(ii) Jobs (processes) are assigned and processor time in a circular method.
(iii) For example take three jobs A, B, C. First the job A is assigned to CPU then job B and job C and then again A, Band C and so on.

Memory Management:
(i) Memory Management is the process of controlling and coordinating computer's main memory and assigning memory block (space) to various running programs to optimize overall computer performance.
(ii) The Memory management involves the allocation of specific memory blocks to individual programs based on user demands. At the application level, memory management ensures the availability of adequate memory for each running program at all times.
(iii) The objective of Memory Management process is to improve both the utilization of the CPU and the speed of the computer's response to its users via main memory. For these reasons, the computers must keep several programs in main memory that associates with many different Memory Management schemes.
(iv) The Operating System is responsible for the following activities in connection with memory management.
(v) Keeping track of which portion of memory are currently being used and who is using them.
(vi) Determining which processes (or parts of processes) and data to move in and out of memory.
(vii) Allocation and de-allocation of memory blocks as needed by the program in main memory. (Garbage Collection).

A Software is a set of instructions that perform a specific task. It interacts basically with the hardware to generate the desired output.
Types of Software
Software is classified into two types:
1. Application Software
2. System Software
Application Software:
Application software is a set of programs to perform specific tasks. For example, MS-word is an application software to create a text document and VLC player is a familiar application software to play audio, video files, and many more.
System Software:
System software is a type of computer program that is designed to run the computer's hardware and application programs. For example Operating System and Language Processor.