[1] OPC Data Access is a group of client–server standards that provides specifications for communicating real-time data from data acquisition devices such as PLCs to display and interface devices like Human–Machine Interfaces (HMI), SCADA systems[2] and also ERP/MES systems.
The OPC Classic specifications are based on the Microsoft COM technology[4] and define a C/C++ interface.
A standard Automation wrapper interface is also defined for access from Visual Basic, Delphi and other automation-enabled languages.
[5] Several vendors offer .NET toolkits to make the OPC interface accessible in .NET applications.
[6] The more recent OPC Unified Architecture allows the same functionality but offers platform independence and optionally complex information modelling capabilities.