Before the 1990s relatively few choices in PID structure were offered. There were also various supplier specific rules as to how to set the proportional mode and integral mode tuning settings to get proportional-only and integral-only control. A different model controller may have been needed for a different structure. The modern DCS offers the flexibility to readily choose 8 structures to take advantage of what each has to offer. Here we take a look at the type of applications where each structure offers an advantage.