Since the beginning of PC-based data acquisition and control in the 1980s, one question has remained a constant consideration for all who would specify a new DAQ system. Is this application better served by an external I/O “box” connected to the PC via some communications link, or an internal “board” system plugged into a slot within the computer? If anything, this question has become more complicated as technology has progressed.

Data transfer rates achievable with a variety of board and external box technologies.

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Choosing what’s best for a given application is not an easy task. Some of the parameters used to compare interfaces are:

• system accuracy,
• I/O count,
• distance between DAQ system and sensors,
• system portability,
• expandability,
• flexibility,
• overall cost,
• bandwidth (DAQ speed),
• expected product life.