The digital sampling oscilloscope is intended for very high frequency operation.
They are used for looking at repetitive signals which have a higher frequency than the sample rate of the scope.
They achieve their performance by collecting samples from several successive waveforms, and then assembling them together. In this way they are able to build up a picture of the waveform.
This technique allows these digital sampling oscilloscopes to view signals at frequencies up to 50 GHz and more.
The design of these scopes is optimised for very high frequency operation, and to achieve this the vertical amplifier topology is somewhat different. On entering the vertical amplifier chain, the signal is sampled prior to any amplification to ensure the maximum bandwidth is achieved. After the signal is sampled a lower frequency amplifier / attenuator combination can be used because the signal is effectively at a lower frequency at this stage. However this methodology does reduce the dynamic range of the instrument. Typically the maximum voltage that can be handled is around 3 volts peak to peak and it is not possible to place protection diodes ahead of the sampling diode ring as this would limit the frequency response.
While these oscilloscopes do have their limitations, they are able to display extraordinarily high frequencies. Where this type of frequency response is needed, a digital storage oscilloscope is the only alternative.