Kernel Mode

What is a System Call?

A system call is the controlled interface a user-space program uses to request a privileged service from the operating system kernel, such as reading a file, a…

Kernel Mode vs User Mode

Kernel mode is a privileged CPU execution state where the operating system can execute any instruction and access all hardware directly, while user mode is a r…

What Are the Types of System Calls?

System calls are the controlled entry points through which a user-space program requests a privileged service from the kernel, and they fall into five broad ca…

What Are Protection Rings in an Operating System?

Protection rings are hierarchical privilege levels enforced by the CPU, typically numbered from Ring 0 (most privileged, running the kernel) to Ring 3 (least p…

What Is the System Call Interface in an Operating System?

The system call interface is the well-defined, kernel-validated boundary through which a user-mode application requests privileged operations — like file I/O,…

Trap vs Interrupt: What Is the Difference?

A trap is a synchronous event deliberately raised by the currently executing instruction (such as a system call or a divide-by-zero error), while an interrupt…

How Does Interrupt Handling Work in an OS?

Interrupt handling is the sequence by which the CPU detects an interrupt request, saves the currently running task’s state, looks up and runs a dedicated handl…

What is an Interrupt Vector Table?

An interrupt vector table (IVT) is an array of handler addresses indexed by interrupt or exception number, used by the CPU to jump directly to the correct hand…

What is a Software Interrupt?

A software interrupt is an interrupt deliberately triggered by executing a special CPU instruction from within a running program, most commonly to request a se…

What Are Nested Interrupts and How Are They Handled?

A nested interrupt occurs when a higher-priority interrupt is allowed to preempt a currently executing lower-priority interrupt handler, so the CPU suspends th…

Context Switch vs Mode Switch: What Is the Difference?

A mode switch is the CPU transitioning between user mode and kernel mode privilege levels while staying within the same process, whereas a context switch is th…