A warped rotor causing a pulsating brake pedal is probably number one on the list.
In my neck of the woods, rust is another issue. Even with daily usage the rust builds up on the braking surface of the rotor again causing a pulsation in the brake pedal.
disc brake components
The rotor is the disc in the disc brake system.
If you can see the brake caliper and rotor, then it has disc brakes. If all you see is a large drum then it has shoes. If you can see the front brakes thru the wheels, you can identify disc brakes. If the rear look like the front, then they are also disc brakes. However if the rear look much different, then chances are they are drum.
worn thin
Besides the steering lock the most common are disc brake locks and/or chains.
In case of cost..drum brake is better than disc brake.
Depends on if it's a disc brake or rim braked bike. And then there are differences between brands. Head over to www.parktool.com, www.bicycletutor.com or www.sheldonbrown.com to find out more. For disc brake bikes, see if you can identify the brand, then go visit their website. They often post maintenance instsructions there.
There are many purposes to using a disc brake. Disc brakes are mainly used in industrial drills because the disc brake stops the drill gently so it doesn't overheat.
pad brakes are disc brakes, it's known as changing brake pads for disc setup and changing brake shoes with drum brake setup.
The teves caliper is a single piston disc brake caliper and the akebono caliper is a dual piston disc brake caliper. The teves caliper is a single piston disc brake caliper and the akebono caliper is a dual piston disc brake caliper.
It looks like a hydraulic clamp. When hydraulic pressure is applied with the brake pedal, the caliper clamps the disc brake pads to the disc brake rotor to stop rotation.
With rear drum brake:-The brake drum may be out of round or may have a rust spot in it. -The brake drum may be cracked.With rear disc brake:-The brake disc may have extreme lateral runout or be mounted improperly. -The brake disc may be cracked. This would be dangerous-Combination of soft brake pads and a directional finish on the disc surface. A directional finish may go away with use and take the noise with it.Regardless of brake type:A brake disc or drum mounted to a bent hub flange or bent axle shaft can cause this noise.