Operating Systems and Kernels
Operating Systems and Kernels
An operating system (OS) is not simply what users see on the screen, such as windows, icons, or menus. Although many users think of the graphical interface as the operating system, this view is technically incomplete.
What Is an Operating System?
In a technical sense, the operating system consists of the essential components required for the basic use and administration of a computer system. These include:
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The kernel
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Device drivers
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Boot loader
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Command shell or other user interfaces
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Basic system and file utilities
The Kernel: Core of the Operating System
The kernel is the innermost and most critical part of the operating system. While the user interface is the outer layer, the kernel forms the core internals of the system.
The kernel is responsible for:
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Managing hardware resources
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Providing basic services to all programs
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Controlling access to the CPU, memory, and devices
Because of this central role, the kernel is also called the core, supervisor, or internals of the operating system.
Main Functions of the Kernel
Typical kernel components include:
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Interrupt handlers to respond to hardware events
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A scheduler to share processor time among processes
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Memory management to control process address spaces
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System services such as networking and interprocess communication (IPC)
Kernel Space and User Space
Modern operating systems use hardware protection to separate execution into two modes:
Kernel Space (Kernel Mode)
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Kernel code executes here
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Full access to hardware and memory
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Runs with elevated privileges
User Space (User Mode)
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User applications execute here
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Limited access to system resources
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Cannot directly access hardware or kernel memory
This separation improves security, stability, and fault isolation.
System Calls: Communication with the Kernel
Applications interact with the kernel through system calls.
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Applications usually invoke library functions (such as the C library)
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These library functions may internally use system calls to request kernel services
Examples:
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printf()performs formatting and buffering, then callswrite() -
open()maps almost directly to theopen()system call -
Some functions (e.g.,
strcpy()) do not require kernel involvement
When a system call is executed:
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The kernel runs on behalf of the application
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The kernel executes in process context
This system call interface is the fundamental mechanism through which applications get work done.
Interrupt Handling
The kernel also manages hardware using interrupts:
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Hardware devices generate interrupts to signal events
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Each interrupt has an associated interrupt handler
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The kernel executes the appropriate handler to respond
Example:
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A keyboard interrupt notifies the kernel of new input
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The kernel reads the data and signals readiness for more input
Three Execution States of the CPU
At any moment, a processor is executing exactly one of the following:
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User-space: running user code in a process
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Kernel-space (process context): executing kernel code on behalf of a process
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Kernel-space (interrupt context): handling a hardware interrupt
Even when the system is idle, the kernel is executing an idle process in kernel mode.
Key Takeaway
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The operating system provides the essential environment for program execution
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The kernel is the heart of the operating system
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User applications rely on the kernel through system calls
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Hardware interaction occurs via interrupts
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Clear separation of user space and kernel space ensures safety and efficiency
📌 Summary
The kernel is the privileged core of the operating system that manages hardware, resources, and system services, enabling applications to run safely and efficiently.
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