Which one of the following groups have only input devices ?

Question

UnlockIAS · Accepted Answer

Correct — D, Mouse, Keyboard, Scanner. Every option begins with the same two devices, so the whole question turns on the third item in each group. A device is an input device if it carries data from the outside world into the computer for processing, and an output device if it carries processed data from the computer back out to the user. The mouse is a pointing device: moving it and clicking it sends position and button data to the machine, so it is an input device. The keyboard converts keystrokes into character codes sent to the processor, so it too is an input device. The scanner is the deciding item — it optically reads a physical document or photograph and converts it into a digital image file that goes into the computer, which is input by definition. All three items in (d) therefore point the same way, into the machine, and (d) is the only group that contains nothing else. That makes it the marked answer. The third items in the other three options — printer, projector and monitor — all move information in the opposite direction, out of the computer to a human being, and each of them is a textbook output device.

Why the other options are wrong — (a) The printer is an output device. It takes data the computer has already processed and renders it as a permanent, human-readable copy on paper, which is why printed output is called hard copy as against the soft copy shown on a screen. Nothing about a printer feeds data into the processor, so the group is not 'only input devices'. The one caution worth carrying is that a modern multifunction machine that both prints and scans is doing two different jobs, and its scanning half is what counts as input — a plain printer is output only.  (b) The projector is an output device. It receives a video signal from the computer and throws an enlarged image onto a screen or wall for an audience to see, which is exactly the outward direction of an output device. It is really a monitor with a longer throw distance; the fact that it sits away from the desk and looks unlike a screen is what makes it feel unfamiliar enough to pick.  (c) The monitor, or visual display unit, is the standard output device — it converts the computer's video signal into the picture you look at. It is the most commonly chosen wrong answer because a monitor is the part of a computer people interact with most and so feels like the centre of the conversation. Direction is what decides it: you read a monitor, you do not feed it. The one exception, worth knowing but not applicable here, is a touchscreen, which is a monitor with a touch-sensitive layer bonded to it and is therefore both an input and an output device.

Concept: A computer system is conventionally described as four functional blocks: input, processing (the CPU, comprising the control unit and the arithmetic and logic unit), storage (primary memory and secondary storage) and output. Peripherals are classified by which of the two doors they stand in. An input device converts a physical action or a physical medium — a keystroke, a hand movement, a printed page, a sound, a fingerprint — into the digital form the processor can work on. An output device does the reverse, converting the processor's digital result into something a human can see, hear or hold. Classifying peripherals correctly under this single rule is the entire skill this question tests, and it is one of the most repeated items in the computer-awareness section of State PCS papers.

State PCS 2024 Q104 — Science & Technology PYQ with Answer

State PCS 2024 Q104 — Science & Technology PYQ with Answer