Which one of the following pairs with respect to computer is not correctly matched?

The pair in option 4 is incorrectly matched. A plotter is a specialized output device used to generate high-quality, accurate, and detailed vector graphics, often used by architects and engineers. The description provided in the option—converting digital electronic signals to communication channel signals and vice versa—actually defines a modem (modulator-demodulator). Other options are correct: 1 megabyte is indeed 1024 x 1024 bytes (1,048,576 bytes) in binary calculation. A compiler is a program that translates high-level language source code into machine language that the hardware can execute. Liveware refers to the human element of a computer system, including the users, programmers, and operators who interact with and maintain the system.