What is the primary function of a bus line in computer systems?

The primary function of a bus line in computer systems is to facilitate the transfer of data between different components of the computer, such as the CPU, memory, and input/output devices. A bus acts as a communication pathway that allows these components to communicate with each other by sending and receiving data signals.

In this context, the bus line is responsible for transporting data and control signals across the various parts of the computer, enabling them to work together efficiently. By establishing a standardized connection, it allows multiple components to access a common set of data lines, reducing the number of physical connections needed and simplifying the architecture of the computer.

The other options, while they describe functions related to a computer system, do not accurately capture the primary role of a bus line. Control of the CPU's speed, managing input from devices, and directing output to storage devices involve different mechanisms and components within the system rather than the bus itself. Thus, the emphasis on data transfer makes the selection of option B correct in this context.