Sidepulls were lighter, but not as powerful as centerpulls, which had a greater mechanical advantage. Dual-pivots were a kind of hybrid between the two types, providing greater power at the cost of a heavier unit.
Photo above shows the rear of the single-pivot brake.
The caliper arms have been hollowed out to reduce weight. Below, the face of the brake. Click on the images to see a larger version. If anything, they are somewhat of a throwback to an earlier day. The front brake for Record and Chorus remains the same as in 2000.