Glossary Updates12 new terms added to the glossaries · October 2, 2026, 22:44 CEST
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Glossary · Industrial communication

OPC Classic

Also known as: Classic OPC, OPC COM/DCOM

German: OPC Classic

In industrial communication, OPC Classic is the first generation of OPC specifications, based on Microsoft COM/DCOM, comprising mainly OPC Data Access (DA), OPC Historical Data Access (HDA) and OPC Alarms & Events (A&E).

  • Industrial communication
  • Standards

In one sentence

OPC Classic is the COM/DCOM-based first OPC generation, mainly OPC DA, HDA and A&E, bound to Windows.

Example

A 2008 SCADA system reads controller tags through an OPC DA server on the same Windows computer; remote access would need DCOM configuration.

How it applies

  • Engineering: OPC Classic is still found in many existing plants. It works reliably on a single computer; across networks it depends on DCOM, which needs complex permissions and firewall openings.
  • Security: Microsoft's DCOM hardening changes have broken some OPC Classic connections between computers. Plants use tunnelling tools or move to OPC UA. Classic servers also depend on Windows versions that may be out of support.
  • Migration: OPC UA wrappers and proxies expose Classic servers as OPC UA servers and vice versa, allowing step-by-step migration.
  • Documentation: The documentation team names the exact specifications and versions a product supports (for example OPC DA 2.05a and 3.0), the Windows versions tested and the DCOM or tunnelling configuration used.

OPC Classic vs. OPC UA

OPC Classic is Windows-bound and split into separate specifications. OPC Unified Architecture (OPC UA) is platform-independent, secure by design and integrates data, history, alarms and methods in one information model.

By knowledge.aitechdoc.world · Published September 26, 2026 · Last reviewed

Source: AI TechDoc Blog editorial definition, based on OPC Foundation specifications

Definitions follow the cited standards and specifications. Where a source is a copyrighted publication, such as an ISO, IEC or EN standard, the definition is a close paraphrase, not a verbatim quotation, so as not to infringe copyright. We recommend reading the original publication. The sections “How it applies” are editorial commentary by AI TechDoc Blog and are not part of any standard.

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