{"id":"opc-classic-da","model_id":"OPC DA","name":"OPC Data Access (OPC DA)","summary":"OPC Data Access (OPC DA) is one of the OPC Classic specifications, which are based on Microsoft Windows COM/DCOM technology for exchanging data between software components. OPC DA defines the exchange of process data including values, time information and quality information. It is defined separately from OPC Alarms & Events (OPC A&E), which covers alarm and event messages and variable states, and OPC Historical Data Access (OPC HDA), which covers query methods and analytics on historical, time-stamped data.","study_notes":["OPC Classic specifications rely on Microsoft COM/DCOM (Distributed Component Object Model) on Windows for data exchange between software components.","OPC Classic is split into three separate specification groups: Data Access (DA), Alarms & Events (A&E) and Historical Data Access (HDA).","The document states that Microsoft de-emphasized COM and DCOM in favour of cross-platform service-oriented architecture (SOA).","The OPC Foundation released OPC Unified Architecture (OPC UA) in 2008; it integrates all functionality of the existing OPC Classic specifications.","Reasons given for OPC UA include a single set of services for exposing data models, support on non-Microsoft and embedded systems, transport of high-level structured data, and secure access through firewalls.","The document gives no port numbers, packet formats, throughput figures or version numbers for OPC DA."],"safety_notes":[],"sources":[{"url":"https://opcfoundation.org/about/opc-technologies/opc-classic/","title":"Classic - OPC Foundation","accessed":"2026-10-25"}],"verification":{"status":"source_checked","checked_at":"2026-10-25","values":7,"method":"llm_source_check"},"updated_at":"2026-10-25","type":"protocol","spec":{"transports":["other"],"architecture":"client_server","encoding":"binary","default_ports":[],"data_types":[{"name":"value","description":"Data value exchanged as defined by OPC DA."},{"name":"time","description":"Time information exchanged together with the value."},{"name":"quality","description":"Quality information exchanged together with the value."}],"related":["opc-ua"]},"url":"https://machineschema.com/protocol/opc-classic-da","license":"https://creativecommons.org/licenses/by/4.0/"}