Help with oscilloscope

I'm little bit confused. Help me please to make everything clear. I want to buy oscilloscope and found two models suitable for me.

1. Rigol DS1102E


2. Rigol DS1102CA

But I don't understand the difference between them. I read that DS1102E has 1 GSa/s sampling rate and DS1102CA has 2 GSa/s. OK. But what does it give in practice? Both oscilloscopes have a bandwidth of 100MHz, so I won't find a difference in picture of signals on screen. Am I right? So could you explain me what is the meaning of 'sampling rate' and 'bandwidth' for modern oscilloscopes? And what is the difference between these things?

Answer

The same bandwidth means they'll both have the same attenuation for signals. It basically means that 100MHz is the cutoff frequency for both scopes.

The samples per second is the resolution of the scope. If you zoom in on a signal the non-interpolated data points will be 0.5 ns apart for the 2GSa/s scope and 1 ns apart for the 1GSa/s. The rule of thumb ere is you can fairly accurately measure a 100MHz signal with the 1GSa/s scope and a 200MHz signal with the 2GSa/s (~10 samples/Hz)

Obviously the more samples then the better representation of your original signal. You'll just have to weigh that with the cost difference.