Introduction to Operating Systems

Introduction to Operating Systems

• An Operating System (OS) functions as a mediator between users and computer hardware, overseeing resource management and application execution.
• Goals of OS include executing programs, enhancing user-friendliness, and efficiently managing hardware resources.
• The computer system structure consists of hardware, OS, application programs, and users, with the OS serving as an interface among them.
• Users seek convenience and performance, necessitating effective resource management in systems like mainframes and mobile devices.
• The OS may refer to just the kernel or encompass all system and application programs from the vendor.
• The kernel is the OS's core, consistently managing resources and program execution.
• Middleware enhances application development by offering additional services such as databases and multimedia functionalities.

Overview of Computer System Structure

• Multiple CPUs and device controllers are linked through a shared bus for system operation.
• Device controllers interact with the CPU via the OS, managing specific types of devices.
• Device drivers facilitate communication between hardware and the OS, with each device featuring a controller and local buffer for data transfer.
• Interrupts pause CPU tasks to manage urgent events, and the OS is responsible for saving CPU state and determining next actions.
• Input/Output (I/O) can be synchronous (CPU waits for completion) or asynchronous (CPU continues tasks uninterrupted).
• Interrupt-Driven I/O involves device drivers triggering I/O processes and generating interrupts upon task completion.

Storage Structure

• Main Memory (RAM) is volatile, fast storage directly used by the CPU, while secondary storage (e.g., hard drives) is non-volatile and offers larger capacity.
• Storage hierarchy is categorized by speed, cost, and volatility: volatile (e.g., RAM, Cache), non-volatile (e.g., Hard disks, SSDs), primary storage (fast and small), and secondary & tertiary storage (larger and slower).
• Caching accelerates data access by storing copies in faster storage.
• Device drivers deliver a consistent interface for hardware communication with the OS.
• Direct Memory Access (DMA) enables high-speed devices to transfer data directly to memory, bypassing CPU intervention for greater efficiency.

System Initialization

• The bootstrap program is executed at startup to initialize hardware and load the OS kernel into memory.
• System daemons are background services initiated after kernel loading to provide extended functionalities.

Interrupts

• Hardware interrupts signal events from devices (e.g., I/O completion).
• Software interrupts, like exceptions or traps, stem from software errors (e.g., division by zero) or from system calls for OS services.

Multiprogramming (Batch System)

• The multiprogramming system optimizes CPU utilization by maintaining several jobs in memory to ensure continuous job execution.
• Essential OS features include:
  • I/O Routine Management for input/output operations.
  • Efficient Memory Management for allocating resources to multiple jobs.
  • CPU Scheduling to determine job execution order.
  • Device Allocation to manage hardware resources for active jobs.