Which component comes in two varieties—one that mechanically writes binary data onto spinning magnetic disks and one that writes data with no mechanical parts?

The system clock is a component that regulates timing signals within a computer, ensuring that processes occur in sync. It does not write or store data; rather, it functions as a timing mechanism for the operation of other components. Therefore, it cannot be categorized as having varieties that involve mechanical or non-mechanical data writing.

An expansion bus is a communication system that transfers data between components inside a computer, such as the CPU and peripheral devices. While it enables the addition of components, it does not involve data storage or writing mechanisms, making it unrelated to the question regarding varieties of data writing technologies.

The motherboard serves as the main circuit board that connects all computer components, facilitating communication and power distribution. While it is essential for functionality, it does not have varieties related to data writing mechanisms, as its role is more about integration than data storage.