---
title: "Types of I/O commands"
subject: "Computer Organization and Architecture"
chapter: 7
key: "semester_5/computer_organization_and_architecture:io-commands"
source: https://www.bctengineer.com/q/semester_5/computer_organization_and_architecture/io-commands
site: BCT Engineering
---

# Types of I/O commands

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

- Asked in: 2067 Asar (old course), 4 marks
- Video: [L-4.1 I/O Interface | Input Output Interface | I/O Commands | Computer Architecture | COA | CSA](https://www.youtube.com/watch?v=gy_LyA1RMJw) — Shanu Kuttan CSE Classes
- 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/io-commands
- Whole chapter: https://www.bctengineer.com/md/semester_5/computer_organization_and_architecture/chapter-7

## Question

What are the four types of I/O commands that an interface receives during the communication link between the processor and peripherals?

## Short answer

The four I/O commands are: control to activate and direct the peripheral, status to test conditions like ready or busy, data output to write data from the bus to the device, and data input to read data from the device into the interface buffer.

## Answer

When the processor communicates with a peripheral through the interface, the interface can receive four types of I/O commands:

1. **Control command:** activates the peripheral and tells it what to do (for example rewind a tape, move the disk head, start a motor).
2. **Status command:** tests the conditions of the interface and the device (ready, busy, error) before a transfer begins and after it finishes.
3. **Data output command:** makes the interface take a word from the data bus and send it to the peripheral (a write).
4. **Data input command:** makes the interface take a word from the peripheral and place it in its buffer register so that the processor can read it from the data bus (a read).

## Check yourself

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

1. What does a control command do?
   A. Tests whether the device is ready
   B. Writes a word to memory
   C. Reads a word
   D. Activates the peripheral and tells it what to do, e.g. rewind a tape
   Answer: D. A control command starts an action such as moving the head or starting a motor. (Key point: Control command)

2. When is a status command used?
   A. To test the conditions of the interface and device before and after a transfer
   B. To send data to the printer
   C. To change the clock
   D. To move the disk head
   Answer: A. It checks ready, busy or error conditions. (Key point: Status command)

3. What does a data output command do?
   A. Makes the interface take a word from the data bus and send it to the peripheral
   B. Clears the buffer
   C. Tests errors
   D. Makes the interface take a word from the peripheral
   Answer: A. Data output is a write to the peripheral. (Key point: Data output)

4. In a data input command, where is the word placed?
   A. In the ALU
   B. Directly in memory
   C. In the printer
   D. In the interface buffer register so the processor can read it from the data bus
   Answer: D. The interface buffers the peripheral word for the processor to read. (Key point: Data input)

## Related in other subjects

- [Largest of four integers processor](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Aspp-largest-of-four) — Embedded System, chapter 2
- [Two-wire vs four-wire communication](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Atwo-vs-four-wire) — Telecommunications, chapter 2
- [Control methods for interface communication](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Ainterfacing-control-methods) — Embedded System, chapter 5
- [Selecting a processor or microcontroller](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aprocessor-selection) — Instrumentation II, chapter 1, asked 4×