(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 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.

Microsoft Windows is a family of proprietary operating systems designed by Microsoft Corporation and primarily targeted to Intel architecture-based computers. Windows comes as pre-loaded on most of the new personal computers and laptops.

Microsoft Windows Home Screen
iOS - iPhone OS
iOS (formerly iPhone OS) is a mobile operating system created and developed by Apple Inc. exclusively for its hardware. It is the operating system that presently powers many of the company's mobile devices, including the iPhone, iPad and iPod Touch. It is the second most popular mobile operating system globally after Android.

    iPhone Home Screen

(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 RobinScheduling :
(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.

(i) File management is an important function of OS which handles the data storage techniques. The operating System manages the files, folders and directory systems on a computer.
(ii) Any type of data in a computer is stored in the form of files and directories/folders through File Allocation Table (FAT).
(iii) The FAT stores general information about files like filename, type (text or binary), size, starting address and access mode (sequential/indexed / indexed-sequential/direct/relative).
(iv) The file manager of the operating system helps to create, edit, copy, allocate memory to the files and also. updates the FAT.
(v) The OS also takes care of the files that are opened with proper access rights to read or edit them. There are few other file management techniques available like Next Generation File System (NTFS) and ext2(Linux).

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).