To explain an input-output choice, name the device, state what it does in this task, and give a reason that comes from the situation, not from a general fact about the device.
This lesson comes after comparing memory and storage and belongs to hardware and processing. It prepares you for the last lesson, keeping your answer inside the model.
What structure makes a justification work?
Use four short steps:
- Task: what must the system do, and what kind of data is involved (text, numbers, sound, a reading, a code)?
- Device: which input or output device fits that data?
- Reason: which feature of the device matches the situation (speed, accuracy, no training needed, works for the user)?
- Limit (optional): one honest drawback, if the question asks you to evaluate.
Common input devices include a keyboard, mouse, touch screen, microphone, camera, scanner, barcode or QR scanner and sensors. Common output devices include a monitor, speaker, printer and actuators such as a motor or buzzer.
Worked example
A school canteen installs a self-service ordering kiosk. Students tap what they want, pay and collect a ticket with an order number. Choose and justify an input device and two output devices.
Task: a student must pick items quickly, without typing, in a busy queue.
Input: touch screen. It lets the student select items by tapping pictures. This matches the task because there is no need to type, so it is quick and needs no training. A limit: screens can get dirty and need cleaning.
Output 1: the same screen. It shows the menu, the chosen items and the total, so the student can check the order before paying.
Output 2: a ticket printer. It prints the order number on paper so the student can collect the food. This matches the task because the number is still readable if the student puts the phone away.
Each choice follows the same shape: device, what it does here, reason from the situation.
The mistake to watch for
The usual error is a device named with a reason that would fit any situation.
Mistaken answer: “A touch screen is used because it is fast and modern.”
This reason is true of almost any device in any question, so it earns little.
Correct it by pointing back to the task. For example: “A touch screen is used because students can choose food by tapping pictures without typing. This means the queue moves quickly”.
Underline the words in the question that describe the user and the place. Make sure your reason uses them.
Check yourself
1. A warehouse worker needs to record hundreds of boxes quickly as they are delivered. Suggest an input device and justify it.
Show answer
A barcode scanner (or QR scanner). Each box carries a code, so scanning records it in one quick action with fewer typing errors than a keyboard.
2. A car warns the driver when it is close to an object while reversing. Name one input device and one output device.
Show answer
Input: a distance (proximity) sensor at the rear measuring how close the object is. Output: a buzzer (or speaker) that sounds faster as the object gets nearer, so the driver does not need to look away.
3. A visually impaired student uses a computer. Suggest an output device that suits them and give a reason.
Show answer
A speaker (or headphones) with software that reads the screen aloud. The student receives the information by sound instead of needing to see the screen.
Where this leads next
Carry on to keeping your answer inside the model, then try the practice set. The safe Python reasoning sandbox can help you experiment with how a sensor reading changes a decision in a small program.
Many students know plenty of devices but run out of reasons under exam pressure. A teacher can help you build one clear reason per device in online one-to-one Computer Science tuition.