Input-Output Devices and CPU Components — Patwari Notes
The difference between input devices, output devices and the components of the CPU (ALU, Control Unit, Registers) — a hardware classification asked about repeatedly in actual Patwari PYQs, explained here with examples.
- RSCIT-level depth
- 7 min read
The Three Main Categories of Hardware
Computer hardware is divided into three main categories — input devices (which send data into the computer), output devices (which show the processed result to the outside), and the CPU/storage (which process and store data). Exams often show a device and ask whether it is an input or an output device.
Input Devices
| Device | Use |
|---|---|
| Keyboard | For typing text and commands |
| Mouse | For moving the pointer on the screen and clicking |
| Scanner | For bringing a paper document/picture into the computer in digital form |
| Microphone | For giving input by converting sound into a digital signal |
| Webcam | For live video/picture input |
| Joystick | For directional control in gaming and simulation |
| Light Pen | For writing/drawing directly on the screen |
| Touchscreen | For giving input by touching the screen directly (smartphones, tablets) |
| Barcode Reader | For reading barcodes printed on products (billing in shops) |
| OMR (Optical Mark Reader) | For reading the bubbles filled in on an exam's OMR sheet |
Output Devices
| Device | Use |
|---|---|
| Monitor (VDU) | For showing the processed result on screen |
| Printer | For printing the result on paper |
| Speaker | For sound output |
| Projector | For showing the screen's content on a large display |
| Plotter | For printing large-sized engineering/design drawings |
A monitor is also called a VDU (Visual/Video Display Unit) — it is an output device, not part of the CPU (see below).
Components of the CPU — Different from Input/Output Devices
The CPU (Central Processing Unit) is the computer's 'brain' and has three main components — the ALU (Arithmetic Logic Unit: performs mathematical and logical calculations), the Control Unit (coordinates and controls the functioning of all components), and Registers (very fast temporary storage within the CPU). Keep in mind — the VDU (monitor) is a separate output device and is not part of the CPU; exams often ask 'which of these is not a component of the CPU' and include the VDU as an option.
Storage devices (such as a hard disk, SSD, pen drive) keep data safe permanently, whereas RAM (Random Access Memory) is temporary (volatile) memory that is cleared as soon as the computer is switched off.
Memory Trick / Exam Tip
Memory trick: a device that sends data 'in' is an Input device (In = inside), and one that shows the result 'out' is an Output device (Out = outside). Don't mix up scanner and printer — a scanner brings paper into the computer (input), a printer sends from the computer onto paper (output).
Frequently Asked Questions
What is the difference between an input device and an output device?+
Data is sent into the computer through input devices (such as keyboard, mouse, scanner), whereas the processed result is shown to the outside through output devices (such as monitor, printer, speaker).
What are the three main components of the CPU?+
The CPU has three main components — the ALU (mathematical-logical calculation), the Control Unit (control and coordination), and Registers (fast temporary storage). The VDU/monitor is not part of the CPU; it is a separate output device.
Is a mouse an input device or an output device?+
A mouse is an input device — through it, the user sends instructions (pointer movement, clicks) to the computer.
Where is an OMR used?+
An OMR (Optical Mark Reader) is used in exams to automatically read the bubbles filled in by a candidate on an OMR answer sheet.
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