Standards for interconnecting instruments date back to the mid-1960s when Hewlett-Packard (now Agilent Technologies) developed the HP-IB, or Hewlett-Packard interface bus, also known as GPIB (general-purpose interface bus).
This very popular international standard is widely used by test and measurement engineers. It's governed by the IEEE-488 standard in the U.S. and the IEC-60625 standard internationally. GPIB is a byte serial bit parallel bus that allows up to 15 instruments to be connected to a single controller (computer). It has a maximum data rate of 1 Mbyte/s.
In the late 1980s, the VXI specification emerged. Based on the VMEbus, it combines the GPIB's ease-of-integration advantages with the VMEbus' speed. The VMEbus' backplane can transfer data at up to 40 Mbytes/s. However, VXI is an expensive interconnect standard that can run two to three times the price of GPIB.
In 1997, National Instruments came up with the PXI specification based on the CompactPCI (cPCI) bus. This Windows-based interconnection method was an instant hit. It offers the choice of mid-level complexity and an intermediate price between the GPIB and VXI, plus it's faster than VXI. It can transfer data at up to 132 Mbytes/s (264 Mbytes/s peak).