 One important characteristic to consider when choosing an op amp is its rail-to-rail capability. Each voltage level supplied to the op amp is called a rail, so a typical 5 volt powered project has two rails, one ground at 0 volts and one at positive 5 volts. With this supply, a rail-to-rail op amp could output a signal ranging all the way from 0 on up to a full 5 volts. This common LM-258 op amp is wired up as a buffer. It'll try to output a copy of its input signal. So, if I feed it a sine wave measuring 3 volts peak-to-peak and centered at 2.5 volts, it reproduces a nice clean copy of the wave at its output. But when I increase the wave's amplitude to 5 volts peak-to-peak, the output is clipped. The chip only has 1.5 volts of headroom. I can't quite reach that top rail. If only we had something better.