Digital Osciloscope sampling real time and equal?

[fala]

Hello, I'm planning to buy a good digital oscilloscope, I have brochures of some of them. In one brochure, it has been claimed that the oscilloscope has 200 MS/s real time and 25 Giga sample/Sec equal sampling, what are they especially equal sampling because I can't imagine that an ADC can sample up to 25Gs/sec. is it important to have higher equal sampling?
One thing else, to calculate how long memory of a digital oscilloscope can hold data I calculate this way, please confirm that my calculations are right.
For example if oscilloscope has
-32 Kbyte/Channel
-8 bit sampling
then for 200 MS/Sec it should be able to hold 160 uSec data

 

[maxascent]

The real time mode is for capturing non periodic signals such as signals that occur once like glitches. The equivalent sampling mode is for periodic waveforms like sine waves. The scope is able to sample at such a high rate by taking multiple aquistions and then combining them to form the signal. That is why the signal must be periodic for this mode. The limiting factor for capturing a signal is the scopes analogue bandwidth. If this was 60MHz then this would be the highest freq signal you could capture. You need to sample at around 4x faster than the signal you are capturing. So for a 60MHz signal you would need to sample at 240MS/s