The Purdue Reference Model is a layered architecture for industrial control systems. It separates enterprise IT, supervisory control, basic control, the physical process, and safety-related functions into distinct zones. This model matters because OT networks control machinery and must preserve availability, timing, and safety; controls that work in office networks can break deterministic plant operations if applied without care.
In defense, the model helps engineers place segmentation, monitoring, and remote access controls at safe boundaries such as jump hosts, firewalls, and management zones. In attacks, defenders often use the model to understand where an intruder may move from business systems into controllers or safety systems. Its main value is practical: it gives teams a shared map for reducing lateral movement and limiting blast radius without disrupting the process.