Introduction to Operating Systems (OS)

Introduction to Operating Systems (OS)

• OS acts as an intermediary between the user and computer hardware, providing a suitable environment for running programs.
• OS objectives include executing user programs, simplifying user problems, providing a convenient environment, and maximizing resource utilization (efficiently).

Kernel

• The kernel is a crucial part of the OS that cannot be disabled while the computer is running.
• It essentially serves as the core of the OS.
• Kernel's role includes memory management, process management, device drivers, and system calls/security.

System Programs

• System programs create the environment for executing and running other applications.
• They provide services to the users. Examples include Assembler, Compiler, and Command Line.

Application Programs

• Application programs are not directly linked to the OS; they work independently.
• These are programs like Adobe, VLC, Notepad, and various games.

Middleware

• These are software frameworks that deliver extra services to application developers.
• They are built into general-purpose OS and are present in mobile computing systems.
• Examples include frameworks for databases, multimedia, and graphics.

Computer Types

• Mainframe Computers: A single large computer with multiple terminals (dumb terminals without memory or processor) connected to it.
• Minicomputers: Mid-range multi-user computers.
• Servers: Dedicated networked computers providing specific services and handling requests from other computers. Their hardware is powerful and designed for continuous operation.

Embedded Systems

• Embedded systems are information processing systems integrated into larger products.
• They are often invisible to the user, with limited or no user interface. (e.g., car systems).
• Users prioritize ease of use and high performance; resource consumption isn't a significant concern.

Computer Components

• Users: Rely on an OS for easy use and high performance.
• Application Programs: Solve user problems using available resources.
• Operating System: Manages the use of hardware resources for different applications.
• Hardware: Contains all the components such as the CPU, memory, and I/O devices.

Controllers

• Controllers, also known as Adapters, manage devices.
• They can be integrated into the device or external.
• The OS communicates with controllers through software called Device Drivers.
• Each controller has a temporary storage area called a buffer.
• Multiple CPUs and device controllers share access to memory through shared bus lines.

Interrupts

• An interrupt is a signal that notifies the CPU of a specific event.
• Hardware interrupts are electrical pulses from hardware devices.
• Software interrupts occur due to programming errors (e.g., division by zero), system calls, or infinite loops.
• By sending an interrupt, the controller informs the CPU that it has completed its task.

Time Frame for I/O Interrupts

• The CPU's activity is represented by peaks, and valleys occur when an I/O interrupt alerts the CPU.
• Output for the I/O is represented by valleys, where the controller writes to memory.
• Direct Memory Access (DMA) is used for high-speed data transfers between devices and memory.

Memory Hierarchy

• The hierarchy of memory consists of various levels with various characteristics.
• Registers are the fastest level, followed by the cache, main memory, magnetic disks, and magnetic tapes.
• Volatile memory loses its content when the computer is turned off; non-volatile memory retains data.

System Calls Interface

• System calls are codes that enable programs and applications to request services from the OS.
• Each system call has a unique number that identifies its function.
• The kernel executes system calls in kernel mode (privileged mode).

Single and Multiprocessing

• Single Processor: A single processor for a single task.
• Multiprocessor: Systems using parallel or tightly-coupled systems.
• Advantages of multiprocessors include increased efficiency, reduced cost, and higher reliability.

Multiprogramming

• Multiprogramming: Allows the CPU and I/O devices to utilize their time effectively.
• The OS schedules tasks (jobs) to run in a timely manner.