Interrupts are broadly classified based on their origin and behavior:

Hardware Interrupts (External Interrupts):

• Source: Originate from external I/O devices or other hardware components, completely asynchronous to the CPU's current program execution. They are signals on physical wires.
• Examples:
• Keyboard/Mouse: A key press or mouse movement triggers an interrupt.
• Disk Drive: Signals completion of a read/write operation, or an error.
• Network Interface Card (NIC): Indicates arrival of a network packet.
• Timer: A programmable timer chip generates an interrupt at regular intervals, crucial for operating system time-slicing and scheduling.
• Power Supply: A warning signal indicating imminent power failure (often a Non-Maskable Interrupt).
• USB Device: A new USB device has been plugged in or data is ready.
• Reset: A dedicated hardware line that forces the CPU to reinitialize.

Software Interrupts (Internal Interrupts / Traps / Exceptions):

• Source: Generated by the execution of a program instruction itself, or by an internal CPU event during instruction execution. They are synchronous, meaning they occur predictably at specific points in the instruction stream.
• Traps (Intentional):
• Concept: These are explicitly generated by a program using a special instruction (e.g., INT n in x86, SYSCALL in MIPS/ARM). They are intentional calls to the operating system kernel.
• Purpose: User programs cannot directly access privileged hardware resources (like I/O ports, memory management units). They use traps to request services from the operating system kernel (e.g., opening a file, reading from the keyboard, allocating memory, creating a process). The trap causes a switch from user mode to privileged kernel mode.
• Exceptions (Unintentional):
• Concept: These are synchronous events caused by an abnormal or erroneous condition that arises during the execution of a CPU instruction. They signal a problem that the CPU itself detected.
• Examples: Divide-by-Zero, Invalid Opcode, Page Fault, Protection Violation, Bus Error.
• Handling: The CPU detects the exception, automatically saves context, and jumps to a specific exception handler routine to diagnose and potentially recover from the error.

Vectored vs. Non-Vectored Interrupts:

• Vectored Interrupts:
• Mechanism: When an I/O device asserts an interrupt, it simultaneously provides the CPU with a unique numerical identifier, often called an interrupt vector or interrupt number.
• ISR Dispatch: The CPU uses this interrupt vector directly as an index into a predefined Interrupt Vector Table (IVT).
• Advantages: Fast dispatch to the correct ISR based on the vector ID without polling.
• Non-Vectored Interrupts:
• Mechanism: The interrupting device asserts a generic interrupt request line to the CPU but does not provide a unique identifier.
• ISR Dispatch: The OS must identify which device caused the interrupt by checking each device's status registers.
• Disadvantages: Slower response compared to vectored interrupts due to polling.

Interrupt Priority:

• Handling Multiple Concurrent Interrupts Based on Priority Levels:
• Assignment of Priorities: Each interrupt source is assigned a specific priority level, with critical events receiving higher priorities.
• Hardware Prioritization: Uses hardware (the Programmable Interrupt Controller - PIC/APIC) to manage these priorities, ensuring higher priority interrupts are serviced first.
• Software Priority Management: When processing an ISR for a lower-priority interrupt, if a higher-priority interrupt occurs, it can preempt the current ISR.

Maskable vs. Non-Maskable Interrupts (NMI):

• Maskable Interrupts: These can be temporarily disabled or 'masked' by the CPU, allowing for critical code sections to run without interruption.
• Non-Maskable Interrupts (NMI): These are high-priority interrupts that cannot be ignored or disabled, meant for critical hardware failures requiring immediate attention.