Operating Systems Concepts

• Operating systems, taught by Prof. Abhijitsinh Parmar from Computer Science & Engineering, are explored.

Core Concepts

• Software is defined as a collection of programs, which are, in turn, collections of code/instructions.
• Hardware refers to the physical devices within a computer system, such as the processor, RAM, hard disk, and I/O devices.

Types of Software

• System software performs system-level tasks, examples are compilers, operating systems, interpreters, linkers and loaders.
• Utility software provides additional functionality to the computer system, examples are calculators, MS Paint, browsers, Notepad and media players.
• Application software is created by users using high-level languages and database systems for specific purposes, like library management, banking, and ticket reservation.

Defining Operating Systems

• An OS is a collection of system software, manages computer hardware resources, and offers common services to computer programs.
• An OS is an intermediary between computer user and hardware and provides an interface.
• Users and processes interact with computer resources by OS.

Goals of an Operating System

• Simplify user program execution and problem solving.
• Use computer hardware efficiently.
• Enable sharing of hardware and software resources.
• Make application software portable and flexible.
• Provide isolation, security, and protection among user programs.
• Increase overall system reliability through error confinement, fault tolerance, and reconfiguration.

Generations of Operating Systems

• The history of operating systems can be split into four generations:
• First Generation (1945-1955): vacuum tubes and plug boards, digital computers weren't constructed until the second world war.
• Calculating engines had mechanical relays, but they were slow and were replaced with vacuum tubes.
• Programming languages and operating systems were nonexistent, programming was performed in machine language, numerical calculations were simple. - Punched cards were introduced in the 1950s, which improved the computer system by replacing plugboards for program input.
• Second Generation (1955-1965): transistors and batch systems, transistors helped manufacture computer systems and sell to customers.
• Resulted in mainframes that were kept in air-conditioned rooms and operated by staff.
• The Batch System was introduced to reduce computer idle time, jobs were collected in input room and were read on magnetic tape.
• Third Generation (1965-1980): integrated circuits and multiprogramming, IBM combined the scientific and commercial computer systems into System/360 using integrated circuits.
• Resulted in price and performance advantages over the second generation systems.
• Multiprogramming was introduced, and the processor was not idle while completing I/O operations by using another job on the processor.
• Fourth Generation (1980-Present): personal computers, development of personal computers became easier using big integrated circuits with thousands of transistors per square centimetre.
• Rise of networks created network and distributed operating systems.
• Users became aware of network usage, and could log in and copy files.

Examples of Personal Computer Operating Systems

• Microsoft Windows, created in the mid-1980s. Current versions: Windows 10 (2015), 8 (2012), 7 (2009), Vista (2007). Comes pre-installed on PCs to be popular.
• Mac OS, operating systems were created by Apple, preinstalled in Macintosh computers/Macs. Notable versions are El Capitan (2015), Yosemite (2014), and Mavericks (2013).
• Linux, family of open-source operating systems that can be changed/distributed with many distributions/versions, and is free.

Mobile Operating Systems

• Mobile devices such as smartphones, tablets, and MP3 can have operating systems, specifically designed for them.
• Examples include Apple iOS and Google Android.

Types of Operating Systems

• Simple Batch System: No direct user interaction, jobs are submitted to operator, and operator places batches of jobs on an input device.
• Multiprogramming Batch System: Several jobs are in memory at once that the CPU processes.
• Multitasking System
• Multiprocessor System
• Distributed Operating System
• Real-time Operating System

Simple Batch Systems

• Increased performance while a job finishes and another starts.
• They are suitable for executing large jobs that need little interaction.
• Do not have much user and computer interaction.
• Do not feature process prioritization.

Multiprogramming Batch Operating Systems

• CPU utilization is increased.
• Multiple jobs loaded into main memory, one chosen for execution by CPU.
• For program in progress requiring service of a peripheral device, control of CPU goes to another job

Multitasking/Time Sharing Systems (TSS).

• TSS extends multiprogramming making more user interaction, and handles multiple interactive jobs.
• The CPU scheduling and multiprogramming is economical to provide system of two or more users.
• Each user gets a time-slice, with context switches being more frequent as one switches after a time of a process duration.
• This gives impression that computer is dedicated to their use, and it's is shared among users.

TSS Advantages/Disadvantages

• Advantage: Quick response and CPU is not idle.
• Disadvantage: Security/integrity needed for user programs/data, system might overload due to high configuration.

Multiprocessor/Parallel Systems

• Have multiple CPUs working in close communication.
• Tightly coupled systems share memory/I/O devices, systems/bus, and uses shared-memory communication.
• A system comprises several processors that share a common physical memory
• Deliver more speed.
• All processors function under one operating system.
• Advantages: Higher throughput , economical because one systems uses 3 CPUs compared to three systems that require peripherals.
• Increased Reliability

Real Time System

• A system (RTOS) promises a certain capability for constriants.
• Known to give time for operations like OS calls and interrupt handling.
• Hard real-time system guarantees operation time which is referred to using critical operations and deadline.

Various Operating Systems

• Soft real-time systems is a critical task and priority over other tasks, they offer security, but cannot be a completion.
• Distributed System has physical processor.
• OS is the part that is used on machines and controls them.
• Loosely coupled systems is that each processor has its low local memory.

Distributed System

• Resources can be shared.
• Fast computation of load.
• Reliability
• Function of system can be extended

Operating System Services

• User interface is required for most operating systems using varying lines, and graphic batches.
• Program needs to be stored, and can must be able to run to end process, and may involve user programs.
• The operating system has read and write files on manipulation.
• The communication can access computer of similar systems.
• The OS also runs error detection and can occur in CPU.

Additional OS Services

• When users need to run concurrently over others, there must be resources to each to of them.
• The device needs special devices etc
• Accounting helps keep track that and what kinda of sources.
• Protection ensures systems access to resources
• Security requires Authentication, and needs protection in information.

System Calls

• Allows programs to receive a service.
• When in user model it provides access for hard ware.
• In Kernel mode can access code.
• Programs are halted and and there is a program crashed. There is process process, system file, directory.

Virtual Machine

• Virtual machine also can abstract hardware computer.
• Is is can have drives, cards into execution runs the same PC.
• Virtual machine is called guest machine.