Introduction to Operating Systems

Introduction to Operating Systems

• An operating system (OS) is a collection of software that manages hardware resources and provides various services to users.
• A computer system comprises a central processing unit (CPU), memory, input/output (I/O) devices, and storage devices. These work together to deliver desired results.
• Computer systems come in diverse forms and sizes, ranging from high-end servers to smartphones.
• Input devices, such as keyboards and mice, provide data and instructions to the computer system.
• The output unit delivers results from computations to the external environment through devices like printers and monitors.
• Storage units hold data and instructions, temporarily (primary storage) or permanently (secondary storage).
• Primary storage (memory) can include RAM, ROM, and cache. Secondary storage includes hard disks and floppy disks and can be magnetic or optical. Primary storage is directly accessible by the CPU.

Computer System Architecture

• A block diagram illustrates the flow of data and signals between computer system components.
• Key components include the CPU, input devices, output devices, and memory units (Figure 1.1).
• Inside the CPU, there is a Control Unit and Arithmetic Logic Unit.
• The Control Unit is the central nervous system of the computer, managing all other units.
• The Arithmetic Logic Unit (ALU) performs calculations (e.g., addition, subtraction, multiplication, division).
• Registers, PC, CIR, AC, MAR, and MDR are examples of specific computer components.

CPU (Central Processing Unit)

• The Arithmetic Logic Unit (ALU) and the Control Unit (CU) work together as the CPU.
• The CPU is the brain of the computer system.
• It performs computations, makes decisions, and controls computer units.

ALU (Arithmetic Logic Unit)

• The ALU performs all calculations like addition, subtraction, multiplication, and division within a computer system.
• The Control Unit (CU) directs the flow of data and instructions to the ALU.
• The result of ALU operations are returned to the storage unit.

CU (Control Unit)

• The Control Unit (CU) controls all other units of the computer.
• It manages the flow of data and instructions to and from the storage unit (memory) and the ALU.
• It is also considered the brain of the system, just like the central nervous system inside a human.

What is Operating System (OS)

• An OS manages hardware.
• The OS hides the complexity of hardware.
• OS serves as intermediary between hardware and user.

Modes of Operation

• Kernel Mode: Has complete access to all hardware. Can execute any instruction.
• User Mode: Limited access to hardware. Can only execute instructions from a specific subset.

Operating Systems (OS) Services

• A program requires loading instructions, data, I/O devices, and initialization tasks.
• The OS handles those requests for the user.
• The OS controls I/O devices, manages resource allocation, and provides services to programs.

Objectives/Goals of Operating Systems

• Hide hardware details from Users
• Provide a convenient interface to the system
• Act as intermediary between Hardware and Users
• Manage computer system resources.

Generations of Operating Systems

• First Generation (1945-1955): Vacuum tubes and plug boards.
• Second Generation (1955-1965): Transistors, and mainframes; Batch systems.
• Third Generation (1965-1980): Integrated circuits (ICs). Multiprogramming offered capability of running several programs concurrently.
• Fourth Generation (1980-Present): Large-Scale Integration (LSI) circuits, Personal Computers (PCs), etc.

Types of Operating Systems

• Mainframe operating systems: Found in large computer systems (e.g., OS/390, OS/360). Offer batch, transaction, and time-sharing processing services.
• Server operating systems: Serve multiple users simultaneously (e.g., Windows Server).
• Multiprocessor operating systems: Run on multiple CPUs, enabling parallel processing. (e.g., Linux, Windows).
• Personal computer operating systems: Designed for single-user environments (e.g., Linux, Windows).
• Handheld operating systems: Run on portable devices (e.g., Symbian OS, Palm OS).
• Embedded operating systems: Designed for specific devices, controlling functions. (e.g., QNX, VxWorks)
• Sensor node operating systems: Run on tiny embedded computers in networks.
• Real-time operating systems: Time is critical; operations must complete within predefined time bounds (e.g., e-Cos).
• Smart card operating systems: Run on credit card-sized devices for security and payment operations.

System Calls

• System calls are a crucial method for programs to interact with the operating system's kernel.
• They facilitate programs' requests for services from the kernel.
• System calls serve as entry points for the kernel (e.g., to perform file management, device management, process control, and communication).

Multiprogramming vs. Multiprocessing vs. Multitasking

• Multiprogramming: Executes multiple programs concurrently on a single CPU by swapping them in and out of main memory.
• Multiprocessing: Executes multiple programs concurrently on multiple CPUs.
• Multitasking: Executes multiple tasks concurrently on a single CPU by rapidly switching between them. It's a form of multiprogramming.

Time-Sharing Operating System

• Allows many users to share a computer's resources simultaneously.
• The computer allocates time slots to different programs to provide concurrent access.
• Mainframes often utilize time-sharing operating systems to facilitate multiple user interactions.

Parallel Processing Operating System

• Designed to speed up program execution by running program fragments concurrently on multiple CPUs.
• Such systems use multiple processors to enhance computation speed.

Distributed Operating System

• Manages applications running across multiple interconnected computers.
• Supports higher-level communication and integration of networked computers.

Views of Operating Systems

• User View: Focuses on the system interface presented to users. Emphasizes ease of use and simple interactions.
• System View: Focuses on how the system interacts with hardware for tasks like resource allocation and I/O control.

Resource Allocation

• The OS manages resources like registers, caches, RAM, ROM, CPUs, and I/O interaction.

Control Program

• This program regulates input and output device interactions with the operating system.
• Handles communication, control, detection, and device management.