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.
Source checked7/7 values · 2026-10-25
Specification
1 source
Transports
other
Architecture
client server
Encoding
binary
Data types
Name
Description
value
Data value exchanged as defined by OPC DA.
time
Time information exchanged together with the value.
quality
Quality information exchanged together with the value.
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.
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