Hi Sharpasacircle. The traditional lockback (rear & mid) has been the mainstay of locking mechanisms for probably the past 100 years.
Keeping in mind that ALL locks operate by putting something in the way of the blade (usually at the tang) so the blade cannot close. removing this "something" is the method of unlocking the blade.
The "new" locks as I remember began with Blackie Collin's "Bolt Action" made by Gerber in the early 80's. Blackie is quite creative and he did 2 things with the bold action. He (1) slid a rod, parrallel to the tang forward over the tang and (2) put a cap on the handle (one piece FRN handle). The rod prevented the tang from closing because the rod was wedged between the tang and the "cap". The force pushing upward when closing against the rod.
a few years later, Michael Walker created the linerlock with a ball bearing detent (for keeping the blade closed). This brought the "wedge" in from the side and prevented the tang from closing at the bottom of the knife. The force pushing backwards through the liner when trying to close against the liner.
Then there came a number of secondary locks that kept the linerlock from closing, thereby making it more reliable. LAWKS from Michael Walker and Ron Lake and the Spyderco "securlock" developed by Frank Centofante and Vince Ford.
I believe the next to come out was the "Rolling Lock" by Bob Taylor. The Rolling lock "rotated" a wedge in the way of the tang and the wedge was held in position by the two liners on both sides.
The Axis lock was being developed about the same time as the Rolling lock. I don't know which was first. The Axis lock uses a rod like the bolt action, but the rod is perpendicular to the tang instead of parrallel, much like the rolling lock. But in the Axis lock, the rod slides forward in slots located in the liners rather than rotate into the locking position like the Rolling lock.
The Arc lock also rotates into postion over the tang like the Rolling lock with the rod (shaft) also being positioned into the liners. I cannot see the difference between the Rolling and Arc locks (patent wise), but I'm sure ther is some small difference.
The Ultra lock is doing the same as the Axis lock, but it is coming in from the front instead of the rear.
The Compression lock (Spyderco) brings in the wedge from the side like the linerlock, but it is at the top of the knife and puts the wedge between the tang and the stop pin. The direction of force is upwards through the stop pin as opposed to the linerlock direction of force being rearward through the liner.
The Ball bearing lock (Spyderco) uses a ball bearing instead of a rod, which moves forward like the bolt action and Axis. Unlike the bolt action in that it is rolling instead of sliding and there is no lever or appendage required to unlock. The ball bearing lock is different from the bolt action and axis lock in that it does not need any liners to keep it in place. In the Dodo, the ball is captured in the radius at the top of the frame and the radius on the tang.
There are more new locks in the works. I just saw a patent n a rotating disc lock. Spyderco is also working on another new lock.
All good, just different.
hope that helps.
sal