The "@" symbol is used to separate the username of an email address from the domain name of the Internet Service Provider (ISP) or email service provider. For example, in the email address "username@example.com," "username" is the username of the email account, and "example.com" is the domain name of the email service provider, separated by the "@" symbol.

A plotter is an output device that prints vector graphics on hard copy. Unlike printers, which are designed for raster graphics and text, plotters are specialized devices used to produce high-quality drawings, diagrams, and other vector-based illustrations. Plotters use pens or other drawing tools to create precise lines and shapes on paper, making them particularly useful for applications that require detailed and accurate graphical output, such as architectural and engineering designs.

All the mentioned errors are handled by OS. The OS is continuously monitoring all of its resources. Also, the OS is constantly detecting and correcting errors.

The data remains the same after saving the file and turning off the computer when it is stored in secondary storage. Secondary storage devices, such as hard drives, solid-state drives, and optical discs, are non-volatile storage media. This means that they retain data even when the power is turned off. Unlike volatile memory (such as RAM), which loses its content when the computer is powered down, data stored in secondary storage remains intact until it is intentionally deleted or modified.

The CPU (Central Processing Unit), motherboard, and RAM (Random Access Memory) are internal components of a computer hardware system. These components are essential for the computer to function and are located inside the computer's casing.