---
title: "Define ISA"
subject: "Computer Organization and Architecture"
chapter: 7
key: "semester_5/computer_organization_and_architecture:isa-define"
source: https://www.bctengineer.com/q/semester_5/computer_organization_and_architecture/isa-define
site: BCT Engineering
---

# Define ISA

Computer Organization and Architecture · Chapter 7: Input-Output Organization

- Asked in: 2067 Asar (old course), 4 marks
- Video: [ISA 1.1 Introduction to the ISA](https://www.youtube.com/watch?v=PlavjNH_RRU) — David Black-Schaffer
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/computer_organization_and_architecture/isa-define
- Whole chapter: https://www.bctengineer.com/md/semester_5/computer_organization_and_architecture/chapter-7

## Question

Define the term ISA.

## Short answer

In Plug and Play, ISA stands for Industry Standard Architecture, the older 8/16-bit expansion bus with jumper‑set resources. In general computing, ISA also means Instruction Set Architecture, the programmer‑visible instructions, registers, and addressing modes.

## Answer

In the context of plug and play, **ISA** is the **Industry Standard Architecture** bus. It is the 8-bit/16-bit expansion bus introduced in the IBM PC/XT/AT, running at about 8 MHz, to which add-on cards (sound card, modem, network card) are connected. Resources such as IRQ lines, DMA channels and I/O addresses of ISA cards were traditionally set by jumpers, which led to conflicts; the PnP ISA specification added automatic configuration to this bus.

(In a general architecture context ISA also means *Instruction Set Architecture*, the set of instructions, registers and addressing modes visible to the programmer.)

## Check yourself

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

1. What is connected to the ISA bus?
   A. Only the power supply
   B. Add-on cards such as sound card, modem and network card
   C. Only memory chips
   D. Only the CPU
   Answer: B. ISA is an expansion bus for add-on cards. (Key point: ISA bus use)

2. Why did ISA cards cause conflicts before PnP?
   A. They were too fast
   B. IRQ, DMA and I/O addresses were set by jumpers by hand
   C. They ran too slowly
   D. They had no resources
   Answer: B. Manual jumper settings led to overlapping resources; PnP ISA added automatic configuration. (Key point: Conflict problem)

3. What else does ISA mean in a general architecture context?
   A. Integrated Storage Array
   B. Interrupt Service Address
   C. Instruction Set Architecture
   D. Industry System Architecture
   Answer: C. It is the set of instructions, registers and addressing modes visible to the programmer. (Key point: Other meaning)