Here’s an example to help us understand the difference: If you live a mile from work, and at 4 pm you tell your wife that you will be home in an hour, you’ve determined the time frame in which to conduct your trip home. Note that your speed will be about 1 mile per hour. But, then things hold you up at work and you don’t get home until 6 pm. What happened? Even though you drove 100 miles an hour all the way home (one mile), the desired effect was not accomplished in the specified time frame. It wasn’t an issue of speed; it was an issue of determinism.
Generally, in the control world on the industrial plant floor, speed and determinism are both needed. Speed is necessary for the greatest possible throughput. Determinism is necessary to define a level of quality for the throughput; that is, the highest speed throughput that is usable.
See also the main November 2011 feature, Understanding Ethernet Speed and Determinism
To read the feature article, click here.