OPC Classic is a family of legacy industrial communication standards that define how control systems, devices, and software applications exchange real-time and historical process data, alarms, and events. It is based on Microsoft COM/DCOM technology and is primarily used in Windows environments.
What OPC Classic includes
OPC Classic commonly refers to several related specifications released before OPC UA, including:
- OPC Data Access (DA) for real-time process values, setpoints, and status
- OPC Alarms & Events (A&E) for alarm and event notifications
- OPC Historical Data Access (HDA) for querying archived process data
These standards define a vendor-neutral interface between OPC servers (data providers such as PLCs, DCS, historians, and SCADA systems) and OPC clients (HMI, MES, reporting, and analytics tools).
Where OPC Classic is used in manufacturing
In industrial and regulated manufacturing environments, OPC Classic commonly appears as:
- A layer between PLCs or DCS systems and SCADA/HMI applications
- A connection between shop floor control systems and MES or data historians
- An interface for collecting process values and alarms used in quality or batch reporting
Because it relies on COM/DCOM, OPC Classic typically runs on on-premises Windows servers or workstations, often within an OT network segment.
What OPC Classic is not
- It is not a security framework or cybersecurity solution.
- It is not a compliance or validation method by itself.
- It is not the same as OPC UA, which is a newer, platform-independent architecture.
OPC Classic provides a standard way to move data; security, reliability, and regulatory suitability depend on the surrounding architecture, hardening, and procedural controls.
Common confusion
- OPC Classic vs OPC UA: OPC Classic uses COM/DCOM and is largely tied to Windows. OPC UA is a newer set of specifications that support platform independence, richer information modeling, and more modern security mechanisms.
- OPC vs compliance: In manufacturing, OPC (including OPC Classic) is often discussed in the context of data integrity or electronic records, but it is a communication standard, not an indication of regulatory compliance.
Relation to broader OPC context
Within the broader OPC Foundation standards, OPC Classic is the earlier generation focused on basic interoperability between industrial systems. Many facilities operate mixed environments where OPC Classic servers and clients coexist with OPC UA gateways or bridges, especially when integrating legacy equipment with newer MES, historian, or analytics platforms.