The vast majority of disc brakes on mountain bikes are hydraulically activated; brake fluid drives pressure to the caliper and this results in a clamping force on your rotor via the brake pads 😉 The physical act of braking is caused by the friction generated by the brake pads and the rotors 😉 Hydraulic disc brakes are lighter, more reliable, feel better and are more powerful than cable actuated disc brakes 🙌 Cable discs however are cheaper and if you already have a bike with cable rim brakes, you don’t need to buy new brake levers as a cable disc brake will use conventional-style cable pull brakes. 
It’s clear to see disc brakes are quickly taking over road bikes. Take a look at the 2018 line-ups of industry leaders like Trek, Scott, and Cannondale. Specialized, Giant and other endurance brands have virtually eliminated rim brakes. Road bikes For 2018, the trend only seems to be heading in one direction. Disk brakes provide safety advantages by offering a much better braking control, regardless of what the condition. They offer a great deal of durability and openness, as well as lower maintenance. Bike design for what typically leads to a more comfortable ride quality. 
I specifically asked people I don’t generally hang with, just to be sure they’re have wining’t try and agree with my point out of friendship. The explanation I gottten from pretty much everyone is that disc brakes won’t give them anything if they are simply trying to win a race. It was still a small amount of weight, but it wasn’t much compared to the extra. Weight of a bike and a rider together can really make a difference when you have a group of equally good cyclers trying To win a race. This is not for those that race. 
The’s researchers finding that bicycling.comA rotor truing tool such as the Jagwire Disc Brake Multitool can bend warped rotors back. Rotate the caliper away from the area that requires truing. To straighten the section, gently move the tool along the rotor. If the rotor has a rubbing area, only this method will work. If you’re unsure if it’s the rotor or the brake, you’re better off taking your bike to a professional to get it done right. Although rotors are powerful stoppers they can be fragile on both sides. “If you do try it yourself, be very gentle,” Perejmybida says. We thank Kesha Okeefe, Samut Prakan Thailand for her help.