Another important attribute is if the amplifier offers “rail-to-rail” performance. Amplifiers typically have a certain amount of headroom on the inputs and outputs. For instance, if an op amp operates from a +/- 5V supply, its input and output signals maybe restricted to a maximum of +/- 4V. So the full range of the power supply rails are not used. A rail-to-rail amplifier can accept inputs and generate output voltages very close to the power supply rails.