Related to the previous post, I recall a technique used in pinball machines. The solenoids are switched in the connction to ground. Say you have a 12V solenoid that you want to operate very fast, so what do you do. You feed it 9V through a series resistor from 24V, that keeps it nice an cool when energized. Then you put a large capacitor from the resistor/solenoid junction to ground. So now when the solenoid is off the capacitor charges to 24V and when you close the switch WHAM! the solenoid get a 24V kick. Pretty soon the capacitor is discharged and the solenoid is held by the nice cool 9V.

Just a bit of related "old fashioned technique" that may still be used in some solenoid activated equipment.

Erik