Enforcement Officer / Accounts Officer (EO/AO) 2020 recruitment test, advertisement 421. Transcribed from the Commission's own booklet (series A, NMJX-U-GTA); answer as per the official UPSC final answer key. This question is in Part B. Answer last reviewed 24 August 2026.

Which one of the following statements is correct ? A device driver of output devices

(a)interprets input provided by users into computer usable form.
(b)interprets computer output into user understandable form.
(c)translates user inputs into output device.
(d)facilitates user to communicate with output device.

Answer

Why

Correct — B, (b) interprets computer output into user understandable form. Read the stem's second line before the options: the sentence being completed is about a device driver of OUTPUT devices, and the direction of travel decides the answer. A device driver is the piece of system software that lets the operating system work a particular piece of hardware. It sits between generic instructions — draw this, print this, play this — and the specific electrical signals, command language and timing that one make and model of device understands. For an output device the traffic runs from the machine towards the person: the computer holds its output as bits, and the driver renders that internal representation into whatever the device needs in order to present it in a form a human can take in. A printer driver converts a page held in memory into the page description language and control codes the printer will accept, so that the result is ink on paper a reader can read. A display driver converts the contents of the frame buffer into the signals that light the pixels of a monitor. A sound card driver converts digital samples into the analogue waveform that drives a loudspeaker. In every case the input is computer output and the output is something the user can perceive and understand, which is what option (b) says. The mirror image of this sentence is option (a), and it is a perfectly good description of a driver for an INPUT device — a keyboard, mouse or scanner, where the user's action is converted into a form the computer can use. The examiner has printed both directions and told you in the stem's second line which one is being asked about.

Why the others are wrong

(a)interprets input provided by users into computer usable form. — A true statement about the wrong half of the pipeline. This describes what the driver of an INPUT device does: a keyboard driver turns key-press scan codes into character codes the operating system can use, a mouse driver turns movement and button signals into coordinates and events, a scanner driver turns reflected light readings into an image file. The stem's second line fixes the subject as output devices, so the direction it describes is reversed. Whenever a question prints a statement and its mirror image, the deciding word is almost always in the stem rather than in the options.
(c)translates user inputs into output device. — Faces the wrong way as well, and does not finish its own sentence — a translation is into a form, not 'into an output device'. If it is read charitably as translating the user's input for the benefit of an output device, it is still describing a journey that begins with the user, which is the input side. The driver of an output device begins with data the computer already holds.
(d)facilitates user to communicate with output device. — The closest rival to the keyed statement, and it is close because it is loose. A driver certainly makes a device usable, but the two parties it actually joins are the operating system and the hardware, not the human and the hardware: the user reaches the device through an application and its interface, and the application reaches the device through the driver. The statement also draws no distinction between one kind of device and another — it would read exactly the same about a keyboard driver — whereas the stem asks specifically about drivers of output devices. Option (b) both names the right parties and says something that is true only of the output direction.

Concept

An operating system cannot be written to know every device that will ever be attached to a computer, so the knowledge of a particular device is packaged separately in a device driver. The driver exposes a standard interface upwards, to the operating system, and speaks the device's own language downwards, to the hardware — its registers, command codes, interrupt lines and timing. That is why installing a new printer or graphics card means installing a driver, and why plug-and-play systems try to find and load the right one automatically. Drivers are classified by the direction the data travels through the device they serve. An input-device driver converts what the user does into data the machine can store and process. An output-device driver converts data the machine holds into the form the device needs to present it to the user. Storage devices and network cards need drivers that work in both directions. Much of the operating system's other work with devices is layered around drivers rather than inside them: buffering to smooth the mismatch between a fast processor and a slow device, spooling so that print jobs queue on disk and can be reordered or cancelled while they wait, and interrupt handling so that the processor is not tied up waiting for a device to finish. Drivers commonly run in kernel mode, with the privileges that implies, which is why a defective driver can bring down an entire system while a defective application usually cannot.

This item is built the way many EPFO computer questions are: two of the four options are the same sentence pointed in opposite directions, and the stem carries the word that chooses between them. Because the stem is split across two printed lines and the options complete the second line as a sentence, a candidate who reads only the first line — 'Which one of the following statements is correct ?' — has no way to choose at all and will pick whichever option sounds most like a definition of a driver. The habit worth taking away is to finish reading the stem before looking at the options, and on a completion item to read each option back into the stem's sentence rather than judging it on its own.

Key facts

A device driver is system software that lets the operating system control a specific piece of hardware, presenting a standard interface upwards and speaking the device's own command language downwards.
A driver for an output device converts data the computer holds into the form the device needs in order to present it to the user; a driver for an input device does the converse.
Printers, monitors, plotters, speakers and projectors are output devices; keyboards, mice, scanners, microphones and touch screens are input devices.
A printer driver converts a page held in memory into the printer's page description language and control codes; a display driver converts the frame buffer into signals for the monitor.
Spooling places output such as print jobs in a queue on disk so that a slow device does not hold up the processor, and jobs waiting in the queue can be reordered or cancelled.
Buffering uses memory to absorb the speed mismatch between the processor and a device; interrupts free the processor from polling a device while it works.
Drivers usually execute in kernel mode with high privilege, which is why a faulty driver can crash the whole operating system.
Plug and play describes the operating system detecting attached hardware and loading or requesting the appropriate driver without the user configuring it by hand.

The stem’s second line fixes the direction of travel

(b) Interprets computer output into user understandable form — CORRECT→For an OUTPUT device the traffic runs from the machine towards the person. The computer holds its output as bits, and the driver renders that internal representation into whatever the device needs in order to present it in a form a human can take in. A printer driver converts a page held in memory into the page description language and control codes the printer will accept; a display driver converts the contents of the frame buffer into the signals that light the pixels of a monitor; a sound card driver converts digital samples into the analogue waveform that drives a loudspeaker.

(a) Interprets user input into computer usable form — true, of the wrong half→A perfectly good description of a driver for an INPUT device: a keyboard driver turns key-press scan codes into character codes the operating system can use, a mouse driver turns movement and button signals into coordinates and events, a scanner driver turns reflected light readings into an image file. The examiner has printed both directions and told you in the stem’s second line which one is being asked about.

(c) Translates user inputs into output device — FALSE→It faces the wrong way as well, and it does not finish its own sentence: a translation is into a FORM, not ‘into an output device’. Read charitably, as translating the user’s input for the benefit of an output device, it still describes a journey that begins with the user, which is the input side.

(d) Facilitates user to communicate with output device — the closest rival→Close because it is loose. A driver certainly makes a device usable, but the two parties it actually joins are the operating system and the hardware, not the human and the hardware: the user reaches the device through an application and its interface, and the application reaches the device through the driver. It also draws no distinction between one kind of device and another.

What a driver is for→An operating system cannot be written to know every device that will ever be attached to a computer, so the knowledge of a particular device is packaged separately. The driver exposes a standard interface upwards, to the operating system, and speaks the device’s own language downwards, to the hardware — its registers, command codes, interrupt lines and timing. That is why installing a new printer or graphics card means installing a driver, and why plug-and-play systems try to find and load the right one automatically.

What is layered around drivers rather than inside them→BUFFERING, using memory to absorb the speed mismatch between a fast processor and a slow device. SPOOLING, queuing print jobs on disk so that a slow device does not hold up the processor, with jobs reorderable or cancellable while they wait. INTERRUPT HANDLING, so the processor is not tied up polling a device while it works. Drivers commonly run in kernel mode with high privilege, which is why a defective driver can bring down an entire system while a defective application usually cannot.

Study next

Input and output devices — how each is classified, and the devices that do bothThe layers of input and output management in an operating system — drivers, buffering, spooling, caching and interrupt handlingSystem software against application software, and where the operating system, drivers, utilities and translators sitKernel mode and user mode, and why privilege matters for driver codePeripheral interfaces — USB, HDMI, Bluetooth and the idea of a standard bus that removes device-specific wiringFirmware and the BIOS or UEFI, the code that lets a machine find its devices before any driver is loaded

Common traps

Answering from the first line of the stem alone. The words 'of output devices' sit on the second line and are what choose between two mirror-image options.
Assuming a driver connects the user to the device. It connects the operating system to the device; the user reaches it through an application.
Confusing a device driver with a device controller. The controller is hardware on or near the device; the driver is the software that talks to that controller.
Thinking every driver is one-directional. Storage and network devices need drivers that carry data both ways.
Treating spooling and buffering as jobs done by the driver itself; they are services the operating system layers around it.

The computer blocks return every sitting to the same handful of themes — system software and its parts, the memory hierarchy, input and output devices, storage units, networking and file formats — and they are asked as one-line recall items with terse options. Statement-completion questions of this shape, where the stem runs on into the options, appear a few times a paper and reward reading the whole sentence. Expect at least one item per paper where two options are the same claim reversed.

Related PYQs

EPFO_EOAO_2020_Q66Open & attempt →

Which one of the following is not a language translator ?

(a) Assembler
(b) Linker
(c) Interpreter
(d) Compiler

Answer(b) Linker

The item immediately before this one, separating the three language translators from the linker — another test of which piece of system software does which job.

EPFO_EOAO_2020_Q68Open & attempt →

Which one of the following registers is used to keep track of the next instruction to be executed ?

(a) Memory address register
(b) Memory buffer register
(c) Program counter
(d) Memory data register

Answer(c) Program counter

Moves the same block from software to hardware, asking which register keeps track of the next instruction to be executed.

EPFO_EOAO_2020_Q27Open & attempt →

Which one of the following basic operations for converting raw input data into useful information is not performed by all computers ?

(a) Inputting
(b) Storing
(c) Switching
(d) Outputting

Answer(c) Switching

Tests the input-process-output vocabulary directly, asking which basic operation for turning raw input data into useful information is not performed by all computers.

Practice

practice — not a real PYQ
Which one of the following is an output device ?
- (a)Optical mark reader
- (b)Plotter
- (c)Joystick
- (d)Barcode scanner
Answer(b) Plotter
practice — not a real PYQ
Placing print jobs in a queue on disk so that a slow printer does not hold up the processor is known as :
- (a)Spooling
- (b)Swapping
- (c)Thrashing
- (d)Paging
Answer(a) Spooling

Why