This method is known as polling. The answer depends on many variables in the system, including operating systems, computer speed, data acquisition hardware, code optimization, and programming languages. The following benchmarks were determined using VC/C++ with the KPCI-3108 in a PII 233MHz running Windows NT4. The measured single value I/O timings are:
Analog Input: 466-479 microseconds Analog Output: 428-431 microseconds Digital Input: 412-419 microseconds Digital Output: 415-418 microseconds Win9x and/or VB could have slower speeds.