[LONGHAIR]

Originally Posted by Manbearpig

" This is a mechanically-operated unit which locks when power is applied, giving full power to both tires, and unlocks when you let off the gas."

It can be considered both.

Ah....no, it can't. A "locker" has to have the ability to "un-lock" or it is just a spool. A locker does positively lock together with square edged teeth, no slipping.
I clutch-type "limited slip" (Posi-traction is GM's word) works just like it sounds. It allows one axle to "slip" so that it can go at a different speed. This keeps one tire from squeeling during turns. The "limited" part comes from the friction of the clutches. The amount of pressure applied to them and the amount of "grip" they have affects the amount of slipping. A really tight Posi unit in a really light car may still squeel the inside tire in a low speed sharp turn.

The word "LOCK" in some cases is just a marketing thing that sounds tough. As an example: Eaton's "Gov-lock" .....it is NOT a locking differential. It is a clutch-type posi-traction unit that has a "variable pressure" mechanism that can apply more pressure to the clutches. It never gets any more than a traditional posi, but it it will loosen-up to the point of acting more like an "open" differential.