Pin Loaded with weights you can select starting from very light weights. They are easy to use, safe and very effective at targeting.
Plate loaded uses conventional round plates, the same plates you'd see on barbells. To change the amount of weight on the machine, you need to manually add or remove the plates.
A rack is a frame or shelf, usually with bars or hooks, that is used for holding things or for hanging things on.
http://www.qdhosfitness.com/pin-loaded/