Which of the following lists is comprised of computer hardware only?

Comprehensive and Detailed In-Depth Explanation:

Computer hardware refers to the physical components of a computer system.

Workstation: A high-performance computer designed for technical or scientific applications.

Modem: A device that modulates and demodulates signals for data transmission over communication lines.

Disk drive: A device that reads and/or writes data to a disk storage medium.

Option D lists only physical components, fitting the definition of computer hardware.

In contrast:

Value-added network (option A): A hosted service offering specialized networking services, not a physical component.

Data warehouse (option B): A system used for reporting and data analysis, representing a data storage concept rather than a physical device.

Firewall (option C): While it can be hardware, it is often implemented as software; thus, the term doesn't exclusively denote hardware.

Therefore, option D accurately represents a list of computer hardware components.