The basic structure of a program generated by LDmicro is very similar to that of a commercial PLC; the instructions entered by the user are executed repeatedly, once every cycle time, with the state of the program across those executions maintained explicitly in the user variables.

I expect that LDmicro is somewhat unusual in that it compiles to native code for a general-purpose microcontroller; I have no direct knowledge, but I would guess that most commercial PLCs are interpreted. That introduces a fixed overhead that's significant for very short programs in small micros.