---
title: "Hardware vs software interrupts"
subject: "Microprocessor"
chapter: 5
key: "semester_4/microprocessor:hardware-vs-software-interrupts"
source: https://www.bctengineer.com/q/semester_4/microprocessor/hardware-vs-software-interrupts
site: BCT Engineering
---

# Hardware vs software interrupts

Microprocessor · Chapter 5: Interrupt Operations

- Asked in: 2069 Poush, 2 marks
- Video: [Software Interrupt vs Hardware Interrupt in 8085 Microprocessor: Key Differences](https://www.youtube.com/watch?v=KjO5rZAL7wQ) — Engineering Funda
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/microprocessor/hardware-vs-software-interrupts
- Whole chapter: https://www.bctengineer.com/md/semester_4/microprocessor/chapter-5

## Question

Differentiate between hardware and software interrupts.

## Short answer

Hardware interrupts come from external devices (e.g., NMI, INTR) and are asynchronous and maskable. Software interrupts are caused by instructions (e.g., INT n) and are synchronous and non-maskable.

## Answer

| Basis | Hardware interrupt | Software interrupt |
|---|---|---|
| Source | External device or signal on an interrupt pin | An instruction in the program |
| Examples | 8085: TRAP, RST 5.5/6.5/7.5, INTR; 8086: NMI, INTR | 8085: RST 0–7; 8086: INT n, INT 3, INTO |
| Timing | Asynchronous: can happen at any time | Synchronous: occurs at a known place in the program |
| Masking | Most can be masked (except TRAP, NMI) | Cannot be masked |
| Acknowledge | Needs INTA' (for INTR) | No acknowledge cycle |
| Use | Servicing I/O devices, emergencies | System calls, debugging, exceptions |

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is the source of a hardware interrupt compared with a software interrupt?
   A. An external signal on a pin versus an instruction in the program
   B. An instruction versus an external signal
   C. The stack versus the flags
   D. Both come from instructions but at different speeds
   Answer: A. Hardware interrupts come from external devices; software interrupts are caused by instructions like INT n. (Key point: Source)

2. Which describes the timing of hardware and software interrupts?
   A. Hardware is synchronous; software is asynchronous
   B. Hardware is asynchronous; software is synchronous (at a known program point)
   C. Both are asynchronous
   D. Both occur only at reset
   Answer: B. Hardware interrupts can occur at any time; software interrupts occur where the instruction is placed. (Key point: Timing)

3. Which statement about masking is correct?
   A. Software interrupts can be masked by IF
   B. No hardware interrupt can be masked
   C. Most hardware interrupts can be masked (except TRAP/NMI); software interrupts cannot
   D. Only software interrupts need INTA'
   Answer: C. Software interrupts are always executed, while most hardware interrupts can be masked. (Key point: Masking)

## Related in Microprocessor

- [Hardware interrupts available in 8086](https://www.bctengineer.com/question.md?key=semester_4%2Fmicroprocessor%3A8086-hardware-interrupts) — Microprocessor, chapter 5
- [Software interrupts of 8085](https://www.bctengineer.com/question.md?key=semester_4%2Fmicroprocessor%3A8085-software-interrupts) — Microprocessor, chapter 5
- [Maskable vs non-maskable interrupts](https://www.bctengineer.com/question.md?key=semester_4%2Fmicroprocessor%3Amaskable-vs-nonmaskable) — Microprocessor, chapter 5, asked 2×
- [Interrupt vs polling; interrupts in 8085](https://www.bctengineer.com/question.md?key=semester_4%2Fmicroprocessor%3Ainterrupt-vs-polling-8085) — Microprocessor, chapter 5

## Related in other subjects

- [Audio hardware and audio software](https://www.bctengineer.com/question.md?key=semester_8%2Fmultimedia_system%3Aaudio-hardware-software) — Multimedia System, chapter 2
- [Structured I/O software; SCAN vs SSTF](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Astructured-io-software-scan-vs-sstf) — Operating System, chapter 6
- [Software reliability; waterfall vs prototyping; embedded software](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Asw-reliability-models-embedded) — Instrumentation II, chapter 9