IVI stands for Interchangeable Virtual Instrument. Several years ago, some instrument manufacturers and software vendors (Tek, Fluke, NI, etc.), got together to discuss the issue of replacing instruments and software when the instrument needed to be replaced. The GPIB commands from vendor A for a DMM would be entirely different than the commands from vendor B. Sometimes, model X from vendor A would have different commands than model Y from the same vendor. When the instrument was replaced for whatever reason, the software controlling the instrument needed to be modified. It was decided to further abstract the instrument driver in the form of IVI. Instruments were divided into a few common classes. The initial classes were power supplies, scopes, DMMs, counters, function gen/arbs. The organizers (at ww.ivifoundation.org) looked at the instruments in each class and decided which functions they had in common. For example, all DMMs will be able to measure volts, current, ohms, and they'll have different ranges settings. The IVI driver uses these common functions and translates them to the instrument specific commands. When you write a program with the IVI class functions, you can swap out instrument A with instrument B (assuming both have an IVI driver), with no changes required to your program. There are other benefits to using IVI such as state caching and simulation but it's the interchangability that's the most important. You can use an IVI driver instead of the instrument specific driver. IVI drivers are based on VISA as is most instrument specific drivers and VISA allows the same driver to be used on GPIB,serial, USB, PXI, and Ethernet. There's a couple of reasons that you might not want to use IVI. It does require more software to be installed so it's a bit more complicated to get started. Second, since the IVI class driver is written for those types of commands that are common to all instruments in a class, to use any special features of an instrument, you have to use the IVI instrument specific driver for those functions. If you use a special feature, you've lost the ability to interchange instruments. Also, IVI drivers are written in C and distributed as a DLL. To make any modifications, you have to have the source code and the ability to make changes and re-compile. LabWindows/CVI is normally used for this. Personally, I prefer the native LabVIEW drivers and will only use IVI if that's the only choice. I also have LabWindows/CVI so I'm able to make changes if necessary. Most of the instruments I use do not fall into any of the IVI classes anyway so I'm seldom faced with the issue.
Kind of a long winded answer. I hope I haven't confused you. Good luck.
