Difference Between a Hard and Soft Reset on iPhoneby John Papiewski
Occasionally, an app on your iPhone may freeze up or otherwise malfunction. The iPhone's reset functions will usually restore normal operation. A soft reset, called "restart" in the iPhone user manual, turns the device's power completely off, halting all programs. Under certain circumstances, a troublesome app may prevent the iPhone from completing a soft reset. In that case, a hard reset is necessary.
To do a soft reset on the iPhone, hold down the "Sleep/Wake" button until the red slider appears. Slide the slider with your fingertip to turn the iPhone off. To complete the reset, turn the iPhone on again by holding the "Sleep/Wake" button until you see the Apple logo on the screen. A hard reset has a single step. Hold the "Sleep/Wake" and "Home" buttons down simultaneously for 10 seconds or longer until the screen displays the Apple logo. After a few seconds, the normal home screen appears.
Effect on Power
During a soft reset, the iPhone is turned off. During this time, it draws no power from the battery. When you store the iPhone for more than a few days, leave the power off until you need it again to prevent the battery from draining. During a hard reset, the phone remains powered on.