Drive Belt and Timing Belt

[oj88]

Aside from what has been mentioned.
Drive belts is designed to slip a little when load is applied allowing obsorbtion of force. While timing belt or chain should never slip, jump or slide so as to maintain proper synchronization of cam, balancers, injection pumps and crankshaft.
Engines with timing belts are more silent than those with chains and gears.

I don't think that drive belts (in a car's engine) are designed to slip. If so, you'll be hearing squeals every time the A/C kicks in, for instance.

In fact, squealing is one sign that the belt tensioner needs adjustment or that the belt itself has stretched beyond it's service life.

Most modern cars have wider multi-groove belts that mates with pulleys that have multi-grooves as well. This adds grip between the belt and the pulleys it's turning to mitigate slipping. And since there's less sliding, it's quieter.

(See cross-section of the belts below) The older or traditional belt which was prone to squealing is known as the v-belt (left). While the multi-groove belt is better known as the serpentine belt (right).