Introduction to Operating Systems

• The course covers these topics: Introduction, Processes and Threads, Scheduling, Process Synchronization, Deadlock, Memory Management, Input/Output Management, and Storage Management.

Objectives

• Define operating systems.
• Explain the services provided by operating systems.
• Describe the evolution of operating systems.
• Describe the various types of operating systems and their services.
• Understand the structure of operating systems.

Outline

• Definition of an Operating System
• Operating System Services
• Types of Operating Systems
• Operating System Structure
• History of Operating Systems

What is an Operating System

• An operating system is a program that facilitates interaction between a user and computer hardware.
• Operating system functions as an extended machine, hiding complex implementation details and presenting a virtual machine for easier use.
• As a resource manager, an operating system allocates time and space to each program.

Computer System Components

• Hardware provides the basic computing resources like CPU, memory, and I/O devices.
• The OS controls and coordinates the use of hardware among applications.
• Application programs define how system resources are used to solve computing problems.
• Users are the people, machines, or other computers interacting with the system.

Operating System Objectives

• Convenience: Top-down view, acting as a virtual machine that extends real hardware, hides hardware details, and provides a user-friendly interface.
• Efficiency: Bottom-up view, serving as a resource manager that orderly controls allocation and improves resource utilization.
• Ability to Evolve: Permitting effective development, testing, and introduction of new system functions without disrupting existing services.
• Protection: Allows only authorized access to data, computation, and services.

Operating System Services

• Process Management
• Memory Management
• File Management
• Secondary-Storage Management
• Input/Output Management
• Network Management
• Protection System

Process Management

• A process is a program in execution and needs resources like CPU time, memory, files, and I/O devices to complete tasks.
• Processes are active entities, while programs are passive.
• The OS manages process creation, deletion, suspension, resumption.
• The OS provides mechanisms for process synchronization and communication.

Memory Management

• The OS tracks which parts of memory are being used and by whom.
• The OS decides which processes to load when memory becomes available.
• The OS allocates and deallocates memory space as needed.

File Management

• A file is a collection of related information defined by its creator.
• The OS handles file and directory creation/deletion.
• The OS maps files onto secondary storage and provides file backup on stable storage media.

Secondary-Storage Management

• The OS manages free space, storage allocation, and disk scheduling.

I/O Management

• Since user programs can't directly execute I/O operations, the OS provides a way to perform them.

Protection System

• Protection is a mechanism that controls access to system and user resources by programs, processes, or users.
• The protection mechanism must distinguish authorized/unauthorized usage, specify controls, and provide enforcement.

Kernel

• The kernel is the core of the OS, acting as a bridge between software applications and hardware.
• The kernel manages system resources.
• The kernel handles tasks like running programs, accessing files, and connecting devices.
• The kernel decides the state of incoming processes.
• The kernel facilitates communication between hardware and user applications.
• The kernel ensures efficient and secure multitasking.
• The kernel manages system stability and prevents unauthorized resource access.

Modes of Operation

• Dual-mode operation enables the OS to protect itself and system components.
• User mode is when the computer executes on behalf of a user application.
• Kernel/privileged/supervisor/system mode is when the OS gains control.
• At boot time, hardware starts in kernel mode, loads the OS, and then switches to user mode for applications.

System Calls

• System calls provide an interface to OS-available services.
• System calls are often accessed through an Application Programming Interface (API).
• System calls are used when a program needs to read data from a file and copy it to another.
• Three common APIs include Windows API for Windows, POSIX API for UNIX, Linux, and Mac OS X, and Java API for the Java virtual machine.

Operating System Structure

• General-purpose OSes are large and need to be well-structured by partitioning tasks into components or modules.

Various Structures

• Simple (monolithic structure)
• Layered
• Microkernel
• Module
• Hybrid

Monolithic/Simple Structure

• Does not have well-defined structures and lacks distinction between user and kernel modes, allowing direct access to hardware.
• Advantage: Efficient performance due to single address space and simplicity in design and debugging.
• Disadvantage: Stability issues, difficulty in maintenance, and vulnerability to malicious programs; examples include Linux and Unix.

Layered Approach

• OS is divided into layers built on top of each other.
• The bottom layer is hardware, and the top layer is the user interface.
• Each layer provides a specific functionality and uses functions/services from lower layers.
• Advantage: Easier debugging.
• Disadvantage: Difficult to define layers, requires careful planning, and can be less efficient due to overhead.

Microkernel System Structure

• Removes nonessential components from the kernel and implements them in user space, communication takes place through message passing.
• Mac OS X kernel (Darwin) is partly based on Mach.
• Advantages: More reliable, easier to extend and port to new architectures.
• Disadvantages: Performance overhead in user-kernel space communication, increased complexity requiring more inter-component communication

Module Approach

• Modern OSes implement loadable kernel modules, with the kernel having core components. Additional services are linked via modules.
• Each core component is separate, interacts with others through known interfaces, and loads as needed within the kernel.
• Similar to layers but more flexible since any module can call another; examples include Linux and Solaris.

Hybrid Systems

• Combination of multiple approaches.
• Linux and Solaris are monolithic in the kernel address space, with modular dynamic loading of functionality.
• Windows: Mostly monolithic but with microkernel-like behavior and support for dynamic kernel modules.
• Apple Mac OS X uses a layered, hybrid structure containing Aqua GUI, Cocoa environment, Mach microkernel (memory management, RPCs, IPC), BSD Unix (networking, file systems), I/O kit (device drivers), and kernel extensions (dynamic modules).

Types of Operating Systems

• Batch operating systems
• Distributed operating systems
• Multitasking/Time Sharing OS
• Network operating systems
• Real-time operating systems
• Multiprogramming Operating System
• Multiprocessing Operating System
• Mobile operating systems

Batch Operating Systems

• Do not allow direct interaction; an operator groups similar jobs into batches, which are then processed efficiently.

Batch Advantages

• Multiple users can share the same systems.
• The idle time for the system is less
• Managing large work is easy

Batch Disadvantages

• CPU is not efficiently used and can be idle while waiting
• Other jobs will need to wait for an unknown time if any job fails
• Increased average response time

Distributed Operating Systems

• Run on multiple interconnected computers working together as a single system.
• Individual computers are nodes or hosts with their own processor, memory, and storage, appearing as one cohesive system.
• Key features are suitable for cloud computing, large-scale data processing, distributed databases, and AI.

Distributed Advantages

• If there is a failure, it does not affect the other network communication since its independent.
• Electronic mail increases the data exchange speed.
• Computation is highly fast and durable since resources are being shared
• Reduced load on host computer
• Systems are easily scalable since systems can easily be added to the network.
• Delay in data processing is reduced.

Distributed Disadvantages

• Failure of the main network will stop the entire communication.
• Expensive and not not readily available
• Software is highly complex and not understood well yet

Multitasking/Time Sharing OS

• Allow multiple users to share a single computer simultaneously, dividing CPU time among the users.
• It Enables users to perform interactive tasks concurrently (e.g., Unix, Linux, Windows Server).

Network Operating Systems

• Manage and coordinate network resources.
• It Allows multiple computers to communicate and share data with services like file/printer sharing and network security.

Real-Time Operating Systems

• Prioritizes the timely execution of tasks (microseconds/milliseconds).
• This is crucial for industrial control systems, robotics, and aviation.

Real-time OS Advantages

• Maximum consumption
• Task Shifting
• Focus on application
• Real-time operating system in the embedded system
• Error Free
• Memory allocation

Real-time OS Disadvantages

• Device driver and interrupt signals; it needs specific device drivers and interrupts signal to respond earliest to interrupts.
• Limited tasks
• Uses heavy system resources
• Complex algorithms

Multiprogramming Operating System

• Allows multiple programs to reside in memory simultaneously.
• Efficiently switches CPU attention among different programs.
• Maximizes processor utilization by dividing available CPU time into time slices/quanta.
• Rapid switching gives the illusion of simultaneous execution, but programs are executed sequentially at a fast pace.

Multiprocessing Operating System

• Utilizes multiple processors or cores within a single computer for executing tasks.
• This Improves system performance and enable concurrent execution of various processes.
• Distributes tasks evenly across processors/cores, which maximizes resource utilization.
• Usually deployed in high-performance computing environments.

Mobile Operating Systems

• Powers smartphones, tablets, and other mobile devices.
• Provides a user-friendly interface.
• Supports mobile hardware components.
• Allows access to various applications.
• Android, iOS, and Windows Mobile are some examples.
• Designed for touch-based interaction and provide user-friendly interfaces with icons, menus, and gestures.
• Security and privacy are top priorities due to the storage of sensitive personal data.

History of Operating Systems

• The history of OS had 4 major generations.
• Operating systems were first developed in the late 1950s to manage tape storage.
• In the early 1950s, General Motors Research Lab made the first OS for IBM 701.
• In the mid-1960s, started to use disks
• In the late 1960s, the first version of the Unix OS was developed
• First OS built by Microsoft, DOS, was built in 1981.
• Windows first came to existence in 1985 with a GUI paired with MS-DOS.