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Introduction to Operating Systems

• Operating Systems (OS) act as an intermediary between the user and the hardware.
• Key functions of an OS include running user applications and providing a convenient environment.
• An OS aims to optimize resource utilization by ensuring efficient operation.
• The Kernel is a crucial part of the OS that remains active throughout computer operation.
• System programs enhance the OS and offer user-facing services (e.g., compilers, assemblers).
• Application programs are separate from the OS, including utilities like VLC, Notepad, and games.
• Middleware software frameworks provide additional services (databases, multimedia, graphics) typically found in general-purpose OS.
• Mobile computing often integrates middleware for functionalities.

Hardware Components

• Hardware includes the central processing unit (CPU), memory, and input/output (I/O) devices.
• Adapters/Controllers connect hardware to the system. Individual devices may have controllers (sometimes integrated).
• Software Device Drivers interact with the controllers.
• Controllers often contain buffers to store data temporarily. Controllers operate independently from the main CPU.
• Interrupts enable communication between the CPU and external devices. Devices signal the CPU when they're ready to transfer data.

Interrupts

• Interrupts are signals from hardware or software to the CPU to perform a critical action.
• Interrupt service routines (ISRs) handle interrupts, transferring control to the appropriate functions.
• Hardware interrupts originate from hardware devices, while software interrupts include exceptions like errors (e.g., division by zero) or system calls.

Interrupt Timeline

• CPU activity is represented by peaks, while valleys represent I/O activity.
• I/O device activity corresponds to data transfers.
• Direct Memory Access (DMA) handles data transfer independently to the CPU.

Memory Hierarchy

• Registers, cache, main memory, magnetic disks, optical disks, and magnetic tapes make up the hierarchy.
• Registers have very high speed and low capacity.
• Cache is faster than main memory.
• Main memory is faster than secondary storage.
• Secondary storage is the slowest but largest capacity storage.
• Volatile memory loses data when the power is off (e.g., registers, cache, RAM).
• Non-volatile memory retains data when the power is off (e.g., magnetic disks, optical drives, magnetic tapes).

System Calls Interface

• The system call interface enables programs to request services from the OS.
• It functions as a set of codes used for system calls.
• System calls use special codes to initiate actions, forwarding requests and data to the kernel through registers.

Single and Multiprocessing

• Single processor systems handle only one task at a time.
• Multiprocessor systems (tightly coupled systems) often have multiple CPUs sharing resources.
• Parallel systems are a specific type of multiprocessor system.

Symmetric/Asymmetric Multiprocessing

• Symmetric multiprocessing (SMP) treats all processors equally, coordinating tasks among them.
• Asymmetric multiprocessing assigns specific tasks to particular processors, with one acting as primary.

Multiprogramming vs. Multitasking

• Multiprogramming manages multiple jobs in memory to improve CPU utilization.
• Multitasking (timesharing) allows users to interact with multiple programs simultaneously, allowing each program a short slice of processor time.
• Multiprogramming is a component of multitasking.

Kernel Data Structures

• Data structures in the kernel, such as linked lists, binary search trees, and hash maps, significantly affect system performance.

Computing Environments

• Traditional computing environments consist of stand-alone computers.
• Mobile computing involves devices connected wirelessly.
• Client-server systems feature centralized servers.
• Peer-to-peer systems connect similarly-enabled devices.
• Cloud computing utilizes virtualization and distributed resources.
• Real-time embedded systems necessitate precise timing for critical applications.
• Distributed computing networks connect multiple devices.

Operating System Functions

• Process Management: Manages processes, their creation, and their termination.
• Memory Management: Controls memory allocation for processes.
• File-System Management: Handles directory structures and file operations.
• Mass-Storage Management: Oversees secondary storage.
• I/O Management: Provides a common interface for device drivers.
• Protection and Security: Enables access control and system security.