Input and Output Devices for UPSC ISS looks like the easiest topic in the Computer section, and it is. That is exactly why the paper sets traps inside it rather than asking hard questions.
Quick answer. Peripherals have produced 12 questions in the last ten papers, an average of 1.2 a year, or 3 marks. Almost every one of them is a classification question. Is a webcam input or output. Is a plotter a printer. Which device reads cheques. The knowledge is easy. The sorting is where marks are lost.
Statistics Paper I, Section IV. Syllabus items: input unit, output unit, and hardware including different types of input, output and peripheral devices.
The one thing that decides most of these questions
Ask one question of every device: does information go into the machine, or come out of it?
| Input | Output | Both |
|---|---|---|
| Keyboard, mouse, trackball | Monitor | Touchscreen |
| Scanner, OCR, OMR, MICR | Printer, plotter | Modem |
| Barcode reader, light pen | Speaker, headphones | Network card |
| Joystick, microphone, webcam | Projector | Storage drives |
A webcam is an input device. It has been placed in a list of output devices to see who is paying attention, and it catches people every year because a camera feels like it produces something.
A plotter is an output device. It looks unusual, so candidates hesitate, but it prints. That settles it.
Pointing devices
| Device | What it is |
|---|---|
| Mouse | Controls two dimensional cursor movement. Comes in mechanical and optical types |
| Trackball | An upside down mouse. Stationary, works on any surface, used in CAD |
| Light pen | An electro optical pointing device connected to the visual display unit |
| Touchscreen | Enter data or select by touching the screen directly |
| Joystick | Cursor control in any direction, used in games and flight simulators |
Two traps live in this table. A mouse cannot replace a keyboard for all purposes, because it cannot type. And a joystick is not limited to one particular direction, it moves in all of them. Both of those wordings have appeared as false statements.
Optical and magnetic recognition
Four technologies that sound alike and are constantly swapped in the options.
| Device | Reads | Used for |
|---|---|---|
| OCR | Printed or typed characters, converted to editable text | Digitising documents |
| OMR | The presence or absence of a mark | Objective answer sheets |
| MICR | Characters printed in magnetic ink containing iron oxide | Bank cheques |
| Barcode reader | Vertical lines of varying width | Supermarkets, retail, libraries |
Only OCR is an optical character recognition device. OMR reads marks, not characters. MICR is magnetic, not optical. A question asking which of the three are optical character recognition devices has one answer, and it is OCR alone.
The supermarket question needs care. In real shops the device is a barcode reader. When the options offer only OCR, OMR and MICR, the intended answer is OCR, because it is the only one that reads printed characters on labels. Read every option before you choose, because the honest real world answer may not be on the list.
Display monitors
| Type | Built from | Power use |
|---|---|---|
| CRT | A vacuum tube with a phosphor coated screen | Highest |
| LCD | Liquid crystals in a flat panel | Lower than CRT |
| LED | An LCD panel with LED backlighting | Lowest |
| TFT | A variant of LCD with better image quality | Similar to LCD |
LED uses less power than LCD, not the other way round. A 2016 statement reversed this, and it was the false one in the set.
Inside a cathode ray tube
Three internal components, asked as a list.
| Component | Function |
|---|---|
| Electron gun | Emits the beam of electrons |
| Electromagnetic coils | Steer the beam to the right point |
| Screen | Phosphor coated surface that glows where the beam lands |
All three are internal components of the CRT.
Printers and plotters
| Impact | Non impact | |
|---|---|---|
| How | Strikes an inked ribbon against the paper | No physical contact with the paper |
| Examples | Dot matrix, daisy wheel, drum, line printer | Inkjet, laser, thermal |
| Noise | Loud | Quiet |
| Carbon copies | Possible | Not possible |
A laser printer uses the same underlying technology as a photocopier, which is xerography. That has been asked directly.
A plotter draws continuous lines by moving a pen across the paper, which is why it is used for maps and engineering drawings rather than text. In a flatbed plotter, if the pen speed is increased too much, the lines may become distorted, because the pen cannot keep contact cleanly at high speed.
Resolution and the dpi calculation
Resolution is measured in dots per inch, dpi, for both scanners and printers. It counts dots along each inch, in both directions.
Do not confuse the units. Resolution is dpi. Processor speed is GHz. Memory is bytes.
Worked Example 1: Total dots on a printed page
Rule. Dots on a page = (dpi × width in inches) × (dpi × height in inches)
A laser printer has a resolution of 1200 dpi. A page measures 8 by 10 inches. How many dots can theoretically be printed on one page?
| Step | Working |
|---|---|
| 1. Dots across the width | 1200 × 8 = 9,600 |
| 2. Dots down the height | 1200 × 10 = 12,000 |
| 3. Multiply | 9,600 × 12,000 |
Answer: 115,200,000 dots, which is 115.2 million
dpi applies to both directions. The most common wrong answer comes from multiplying 1200 by the page area of 80 square inches, which gives 96,000 and appears in the options as 0.096 million. You have to square the dpi effect, not apply it once.
Worked Example 2: Sorting a mixed device list
This is the shape most peripheral questions take, so practise the sorting rather than the facts.
Which of the following are output devices? 1. Printer 2. Speaker 3. Plotter 4. Webcam
| Device | Direction | Verdict |
|---|---|---|
| Printer | Produces a hard copy | Output |
| Speaker | Produces sound | Output |
| Plotter | Draws on paper | Output |
| Webcam | Captures video into the machine | Input |
Answer: 1, 2 and 3 only
Ask the same one question of every item on the list and the question answers itself.
Worked Example 3: What forms a terminal
A terminal is the point where a user meets the system. It needs a way to put information in and a way to get information out.
| Component | Role |
|---|---|
| Keyboard | Input |
| Monitor | Output |
A terminal is a keyboard paired with a monitor. A mouse is not required, and a printer is not part of it.
Direct memory access
When a peripheral needs to move a large block of data, having the CPU carry every byte wastes processor time. There are four ways to handle the transfer, and the paper has asked which one frees the CPU.
| Technique | CPU involvement |
|---|---|
| Programmed data transfer | CPU handles every byte |
| Polling | CPU repeatedly checks whether the device is ready |
| Interrupt driven transfer | Device signals the CPU when ready, CPU then transfers |
| Direct memory access, DMA | Device transfers straight to memory with no constant CPU involvement |
DMA is the technique that lets a peripheral transfer data continuously without constant intervention of the CPU. Interrupt driven transfer still needs the CPU for the transfer itself, which is why it is the most tempting wrong answer.
Two small definitions that have been asked
The main function of an input device is to accept data and instructions from the user and convert them into a form the computer can process.
A webcam’s video quality depends on its frame rate and resolution. Higher is better for both. A statement claiming that smooth video needs maximum frame rate and minimum resolution is false.
How This Gets Asked
The classification trap [2021]
Which of the following are output devices? 1. Printer 2. Speaker 3. Plotter 4. Webcam
Printer, speaker and plotter. The webcam is input.
This is the purest form of the peripheral question. No technology, no calculation, just whether you can sort four familiar objects into two boxes under time pressure.
The calculation nobody expects [2026]
A laser printer has a resolution of 1200 dpi. If a page measures 8 by 10 inches, how many total dots can theoretically be printed on one page?
115.2 million.
A calculation, in the peripherals topic, in a Statistics paper. It appeared for the first time in 2026, which is worth noting: the paper is adding arithmetic to areas that used to be pure recall.
The three statement device question [2024]
Consider the following statements: I. Light pen is an electro optical pointing device generally connected to the Visual Display Unit. II. Touchscreen enables us to enter data by directly touching the screen. III. Joystick controls the movement of the cursor by pointing in a particular direction only.
I and II only. The joystick statement fails on two words, “only” and “particular direction“. A joystick moves the cursor in every direction.
Read the qualifiers, not the nouns. Most false statements in this topic are true sentences with one restrictive word added.
Quick Revision Table
| Point | Value |
|---|---|
| Webcam | Input device |
| Plotter | Output device |
| Terminal | Keyboard plus monitor |
| Mouse types | Mechanical and optical |
| Mouse cannot | Replace a keyboard for all purposes |
| Joystick moves | In all directions, not one only |
| Light pen | Electro optical, connected to the VDU |
| OCR reads | Printed characters |
| OMR reads | Marks, used for answer sheets |
| MICR reads | Magnetic ink, used for cheques |
| Barcode reader | Supermarkets and libraries |
| Only optical character recognition device | OCR |
| CRT internal parts | Electron gun, electromagnetic coils, screen |
| Power use, lowest first | LED, then LCD, then CRT |
| Impact printers | Dot matrix, daisy wheel, drum |
| Non impact printers | Inkjet, laser, thermal |
| Laser printer technology | Same as a photocopier |
| Flatbed plotter, pen too fast | Lines may be distorted |
| Resolution unit | dpi |
| Dots on a page | (dpi × width) × (dpi × height) |
| Transfer without CPU intervention | Direct memory access |
| Webcam quality depends on | Frame rate and resolution |
Practice Set
Ten questions. No answer key below.
Write your answers in the comments, all ten in a single comment, in the format 1-b 2-a 3-d and so on. The full answer key is posted in this same thread after seven days.
A year in brackets means the question is from that paper. The rest are written in the same pattern.
- Consider the following statements in respect of a mouse: 1. It controls the two dimensional movement of the cursor on the displayed screen. 2. It is usually of two different types, mechanical and optical. 3. It can be used as an alternate to the keyboard for all purposes. 4. It is an input device. Which of the above statements are correct? [2017]
- Which of the following devices are paired together to form a terminal? [2020]
- Which of the following are the optical character recognition devices? 1. OCR 2. OMR 3. MICR [2020]
- Consider the following components: 1. Electron gun 2. Electromagnetic coils 3. Screen Which of the above are internal components of the Cathode Ray Tube? [2020]
- Which of the following are output devices? 1. Printer 2. Speaker 3. Plotter 4. Webcam [2021]
- Consider the following statements in respect of Webcam: I. It is an input device. II. The quality of the video taken through the Webcam largely depends on frame rate and resolution. III. For a video to be smooth and clear, the frame rate is maximum and resolution is minimum. [2024]
- A flatbed plotter moves its pin in X-Y direction. If the pen speed is increased too much, what will be the effect on drawing quality? [2026]
- Which one of the following techniques is being used by a peripheral device to transfer data continuously without constant intervention of CPU? [2026]
- A laser printer has a resolution of 1200 dpi. If a page measures 8 by 10 inches, how many total dots can theoretically be printed on one page? [2026]
- Consider the following statements: I. An LED monitor consumes less power than an LCD monitor. II. A laser printer is an impact printer. Which of the statements given above is or are correct?
Frequently Asked Questions
How many questions come from input and output devices in UPSC ISS?
Twelve across the ten papers from 2017 to 2026, about 1.2 a year, worth 3 marks. Most of them test classification rather than technology.
Is a webcam an input or output device?
Input. It captures video and sends it into the computer. It has been placed inside lists of output devices as a trap, and it catches candidates every time it appears.
What is the difference between OCR, OMR and MICR?
OCR reads printed characters and converts them to editable text. OMR senses the presence or absence of a mark and is used for answer sheets. MICR reads characters printed in magnetic ink and is used for bank cheques.
Which devices together form a terminal?
A keyboard and a monitor. One provides input, the other output, and together they form the point at which a user interacts with the system.
What is direct memory access?
A technique that allows a peripheral to transfer data straight to memory without the CPU handling every byte. Interrupt driven transfer still needs the CPU for the transfer itself, which makes it the common wrong answer.
How do I calculate the total dots a printer can produce on a page?
Multiply the dots per inch by the width in inches, multiply the dpi by the height in inches, then multiply those two results. The dpi applies in both directions, not to the page area once.
Is a plotter a printer?
A plotter is an output device that draws continuous lines with a moving pen, which suits maps and engineering drawings. A printer forms images from dots. Both are output devices.
Related Reading
- Computer Application for UPSC ISS: Complete 16 Part Series
- Computer Memory for UPSC ISS
- CPU for UPSC ISS
- System Software, Compilers and Assemblers for UPSC ISS
Part 5 of 16 in the Computer Series for UPSC ISS. Previous: Computer Memory for UPSC ISS. Next: System Software, Compilers and Assemblers for UPSC ISS, published 11 October at 8:00 AM.
