Bandwidth is a measure of the range of frequencies that can be displayed, it refers primarily to the vertical amplifier, although the horizontal deflection amplifier has to be fast enough to handle the fastest sweeps. The bandwidth of the oscilloscope is limited by the vertical amplifiers and the CRT (in analog instruments) or by the sampling rate of the analog to digital converter in digital instruments. In an analog oscilloscope, the vertical amplifier acquires the signal to be displayed.The vertical amplifier response is down 3db at some frequency which mainly decides the bandwidth of oscilloscope.