Comparison
OPC UA vs OPC DA (OPC Classic)
OPC DA: "Data Access": is the original OPC standard from the late 1990s. It's Windows-only (built on COM/DCOM) and moves live values with no meaning attached. OPC UA is its modern successor: platform-independent, secure by design, and self-describing. If you're building new, use OPC UA; if you have OPC DA in place, you can bridge it.
At a glance
| OPC DA (Classic) | OPC UA | |
|---|---|---|
| Platform | Windows only (COM/DCOM) | Any OS / embedded / cloud |
| Networking | DCOM: painful across firewalls/subnets | Simple TCP (port 4840), WebSockets, MQTT |
| Security | Relies on Windows/DCOM | Encryption, signing, authentication |
| Data | Values, timestamp, quality only | Rich, typed information model |
| Models | DA / HDA / A&E as separate specs | Unified: data, history, alarms in one |
| Status | Legacy: maintained, not evolving | The active, strategic standard |
Why OPC UA replaced OPC DA
- No more DCOM. DCOM configuration and its firewall/authentication headaches were the single biggest pain of OPC Classic. OPC UA uses a clean TCP protocol instead.
- Security built in. OPC DA had none of its own; OPC UA encrypts, signs and authenticates.
- Meaning, not just values. OPC UA's information model describes what each value is: enabling true interoperability.
- One unified model. Real-time (DA), historical (HDA) and alarms (A&E) are unified in OPC UA instead of three separate interfaces.
Can an OPC DA client talk to an OPC UA server?
Not directly: they're different technologies. You bridge them with a COM/DCOM-to-UA wrapper (also called a proxy or gateway):
- UA wrapper: exposes an existing OPC DA server as an OPC UA server (modern clients reach legacy data).
- UA proxy: lets an old OPC DA/COM client read an OPC UA server.
Most major OPC vendors ship these wrappers, so you rarely have to rip-and-replace: you put OPC UA in front of your OPC DA estate.
How to migrate OPC DA to OPC UA
- Inventory your OPC DA servers and the clients that depend on them.
- Stand up a UA wrapper or edge gateway that reads DA and republishes as OPC UA.
- Point new clients (SCADA, MES, historian, cloud) at the UA endpoint; keep DA running during transition.
- Enable Sign & Encrypt and certificate trust (see security).
- Retire DCOM access once all clients are on UA.
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See Jemba →FAQ
What does OPC DA stand for?
OPC Data Access: the classic OPC interface for reading/writing current process values. "OPC" itself originally stood for OLE for Process Control.
Is OPC the same as OPC UA?
"OPC" colloquially refers to the classic (DA/HDA/A&E) specs. OPC UA is the newer unified architecture. So "OPC vs OPC UA" usually means OPC Classic vs OPC UA.
Is OPC DA obsolete?
It's legacy but still widely deployed. It's maintained for compatibility, while all new development happens in OPC UA.
Last updated 4 September 2026 · Educational resource.