OPERATING SYSTEM • An Operating system (OS) is a software which acts as an interface between the end user and computer hardware. • Every computer must have at least one OS to run other programs. An application like Chrome, MS Word, Games, etc needs some environment in which it will run and perform its task. • 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.

Features of Operating System • 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

Function of an Operating System

1. Process management - Process management helps OS to create and delete processes. It also provides mechanisms for synchronization and communication among processes.
2. Memory management - Memory management module performs the task of allocation and de-allocation of memory space to programs in need of this resources.
3. File management - It manages all the file-related activities such as organization storage, retrieval, naming, sharing, and protection of files.
4. 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.
5. I/O System Management - One of the main objects of any OS is to hide the peculiarities of that hardware devices from the user.
6. 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.
7. Security - Security module protects the data and information of a computer system against malware threat and authorized access.
8. Command interpretation - This module is interpreting commands given by the and acting system resources to process that commands.
9. 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. 10.Job accounting - Keeping track of time & resource used by various job and users. 11.Communication management - Coordination and assignment of compilers, interpreters, and another software resource of the various users of the computer systems.

Classification 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.

Multiprocessing operating system Multiprocessor operating systems are used in operating systems to boost the performance of multiple CPUs within a single computer system. Multiple CPUs are linked together so that a job can be divided and executed more quickly.

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.

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.

The 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.

1. System Programs
2. Application Programs
3. Utilities

UNIX OPERATING SYSTEM:

BASIC STRUCTURE OF UNIX OPERATING SYSTEM:

Figure – system structure