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Virtual instrument software architecture is a widely used application programming interface in the test and measurement industry for communicating with instruments from a computer. VISA is an industry standard implemented by several T&M companies, such as, Anritsu, Bustec, Keysight Technologies, Kikusui, National Instruments, Rohde & Schwarz, and Tektronix.
The VISA standard includes specifications for communication with resources over T&M-specific I/O interfaces such as GPIB and VXI. There are also some specifications for T&M-specific protocols over PC-standard I/O, such as HiSLIP or VXI-11 and USBTMC.
The VISA library has standardized the presentation of its operations over several software reuse mechanisms, including through a C API exposed from Windows DLL, visa32.dll, over the Microsoft COM technology, and through a.NET API. Although there are several VISA vendors and implementations, applications written against VISA are vendor-interchangeable thanks to the standardization of VISA's presentation and operations/capabilities. Implementations from specific vendors are also available for less common programming languages and software reuse technologies.