---
title: "Define PnP POST"
subject: "Computer Organization and Architecture"
chapter: 7
key: "semester_5/computer_organization_and_architecture:pnp-post"
source: https://www.bctengineer.com/q/semester_5/computer_organization_and_architecture/pnp-post
site: BCT Engineering
---

# Define PnP POST

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

- Asked in: 2067 Asar (old course), 4 marks
- 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/pnp-post
- Whole chapter: https://www.bctengineer.com/md/semester_5/computer_organization_and_architecture/chapter-7

## Question

Define the term PnP POST.

## Short answer

PnP POST is the BIOS power‑on self‑test that detects and configures PnP devices. It isolates each card, assigns a card select number, reads resource requirements, resolves conflicts with legacy devices, and assigns IRQ, DMA, and I/O addresses before booting the OS.

## Answer

**PnP POST** is the part of the power-on self-test (POST) of a Plug and Play BIOS that detects and configures PnP devices at start-up. After the basic POST checks of CPU, memory and the boot devices, the PnP BIOS isolates every PnP card on the ISA bus and gives each a card select number (CSN), reads its resource requirements, resolves conflicts with the legacy devices recorded in the ESCD, assigns IRQ, DMA, I/O and memory resources, activates the cards, and then continues to boot the operating system.

## Check yourself

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

1. What is PnP POST?
   A. A printer test
   B. A network protocol
   C. An operating system driver
   D. The part of POST that detects and configures PnP devices at start-up
   Answer: D. After basic POST, the PnP BIOS isolates and configures PnP cards. (Key point: PnP POST meaning)

2. What does the PnP BIOS give each isolated card?
   A. A file name
   B. A card select number (CSN)
   C. A password
   D. A new serial number
   Answer: B. Each card gets a CSN after isolation. (Key point: CSN)

3. How are conflicts with legacy devices avoided?
   A. By using the configuration recorded in the ESCD
   B. By asking the user
   C. By ignoring them
   D. By disabling them
   Answer: A. The BIOS avoids resources recorded in the ESCD. (Key point: Legacy devices)

4. What happens after the cards are activated?
   A. POST starts again
   B. The BIOS continues to boot the operating system
   C. The system powers off
   D. The cards are removed
   Answer: B. Activation is followed by booting the OS. (Key point: Order)