Understanding Operating Systems

What is an Operating System?

• An operating system acts as a bridge between the user and the computer hardware.
• Facilitates user program execution and makes problem-solving easier.
• Enhances the user experience by making the system more convenient to use.
• Optimizes resource usage to ensure efficient hardware utilization.

Computer System Structure

• Four primary components: hardware, operating system, application programs, and users.
• Hardware provides fundamental computing resources, including CPU, memory, and I/O devices.
• The operating system controls and coordinates hardware access for various applications and users.
• Application programs define how system resources are used to solve user computing problems.
• Users can be individuals, machines, or other computers.

Operating System Functions

• The operating system's role varies depending on the perspective.
• Users prioritize ease of use and performance, often overlooking resource utilization.
• Shared systems like mainframes require efficient resource allocation and user program management to ensure optimal service for all users.
• Mobile devices, like smartphones and tablets, prioritize usability and battery life while managing limited resources.
• Embedded computers, often found in devices, typically operate without significant user interaction and are optimized for specific tasks.

Operating System Definition

• No universally accepted definition exists.
• The "kernel" is considered the core operating system component, always running on the computer.
• System programs are included with the operating system but are not part of the kernel.
• Application programs encompass all software not directly associated with the operating system.
• Modern operating systems often include middleware, providing additional services for application developers, like databases and multimedia capabilities.

Computer-System Organization

• Computer systems typically consist of one or more CPUs and device controllers connected via a common bus.
• The bus provides shared memory access for concurrent CPU execution and device competition for memory cycles.

Computer-System Operation

• Each device controller manages a specific device type.
• Each controller has a local buffer for temporary data storage.
• Operating system device drivers are associated with each device controller type, managing its operations.
• The CPU transfers data between main memory and local buffers.
• I/O occurs between the device and the controller's local buffer.
• Device controllers notify the CPU of operation completion through interrupts.

Interrupt Handling

• Interrupts transfer control to the interrupt service routine, typically through an interrupt vector.
• The interrupt architecture saves the address of the interrupted instruction.
• Traps and exceptions are software-generated interrupts triggered by errors or user requests.
• Operating systems are interrupt-driven.

Computer Startup

• The bootstrap program is the first program loaded during power-up or reboot.
• Typically stored in ROM or EPROM, it initializes all system aspects and loads the operating system kernel for execution.

Storage Structure

• Main memory is the only storage directly accessible by the CPU, providing fast, volatile, random access capabilities.
• Secondary storage extends main memory by offering large, nonvolatile storage capacity, using technologies like Hard Disk Drives (HDD) and Non-Volatile Memory (NVM) devices.

Storage Hierarchy

• Storage systems are organized hierarchically based on speed, cost, and volatility.
• Caching involves copying information to faster storage levels, where main memory acts as a cache for secondary storage.
• Device drivers manage I/O for each device controller.