Which additional tool is necessary apart from Philips #2 to service the PowerEdge C6220?

The correct choice in this scenario is the T20 Torx screwdriver. The PowerEdge C6220, like many other Dell server models, incorporates specific types of screws that require a Torx tool for proper service and maintenance. The T20 designation refers to the size of the Torx driver needed, which is essential for accessing various internal components or securing outer panels. Using the correct size is crucial to avoid stripping the screws, ensuring they can be properly tightened or removed without damaging them.

While other tools may be useful for general maintenance or service tasks, they do not meet the specific requirements for the screws used in the PowerEdge C6220. For example, a standard screwdriver or a cruciform screwdriver would not fit the Torx screws, making them ineffective for this particular application. A socket wrench, while useful for certain bolts, would not accommodate the Torx screws either. Therefore, having a T20 Torx screwdriver is necessary for effectively servicing this specific server model.