Which one of the following is not an output device ?

In computer systems, hardware is classified into input and output devices based on the flow of information. Output devices are hardware components that receive data from a computer and translate it into a human-perceivable form.

• Printer: Converts digital documents into physical hard copies.
• Speaker: Converts digital audio signals into sound waves.
• Plotter: A specialized output device used for printing high-quality vector graphics, such as architectural blueprints and engineering designs.

An Optical Mouse, however, is an input device. It uses a light-emitting diode (LED) and a photodetection sensor to track movement across a surface. This data is sent to the computer to control the cursor on the screen. Since it provides data/instructions to the system, it is not an output device.