Physical access control is the set of measures that restrict who can enter a room, touch equipment, or perform maintenance on sensitive systems. It includes locks, badges, biometrics, security guards, mantraps, CCTV, and logged visitor procedures. In cyber security, it matters because many attacks start, or become far easier, once an attacker can reach the hardware directly.
Strong physical controls protect servers, storage, network gear, and specialized devices such as quantum hardware in a shared data centre. They help prevent theft, tampering, rogue device insertion, cable changes, boot-media swaps, and unauthorized console access. Defenders use physical access control alongside network segmentation and monitoring: if someone cannot physically reach a system, they cannot easily bypass software defenses, extract disks, or reset devices into a weaker state. Weak controls can turn a secure environment into a much larger attack surface.