If you're going to start playing around with those, it's helpful to understand which connector takes which pin.
A 15 pin connector is a standard density for example. a 50 pin connector is a high density.
Those are the two that I remember off the top of my head, but there's a chart somewhere that spells this all out.
FYI- if you have a unit that's powered through Hi density pins, don't be surprised if it has two power pins right next to each other. Those little pins can only handle like 3 amps each max