Which of the following is a physical security measure for protecting data centers?

Access controls are a critical physical security measure for protecting data centers. They help ensure that only authorized personnel can access sensitive areas where servers and data infrastructures reside. This can involve various methods such as keycard entry systems, biometrics (like fingerprint or retina scans), or security personnel monitoring who enters and exits the facility. By limiting access to those who have the necessary clearance, data centers can significantly reduce the risk of unauthorized access, theft, or tampering with the data.

Firewalls, encryption software, and incident response plans serve important roles in cybersecurity but do not pertain specifically to the physical security aspect of a data center. Firewalls typically protect networks by controlling incoming and outgoing traffic, while encryption software secures data by converting it into a coded format. Incident response plans are critical for effectively addressing and managing security breaches but do not directly prevent unauthorized physical access to the data center itself. Therefore, the appropriate choice for a physical security measure is indeed access controls.