HP 54710A User's Reference Manual page 26

How the Oscilloscope Works
Data Flow
The digitizer samples the applied signal and converts it to a digital signal.
The FISO holds the data until the system bus is ready for the data. The
output of the FISO is used as an address to the calibration read-through table
(cal table). The cal table automatically applies the calibration factors to the
data.
In the real-time sampling mode, the calibrated data is stored in the channel
memories before any of the postprocessing is performed. Postprocessing
includes turning on or off the digital bandwidth limit filter or the interpolator,
calculating functions, storing data to the waveform memories, transferring
data over the HP-IB bus, or transferring data to and from the disk. Notice
that the measurements are performed on the real-time data after it has gone
through postprocessing.
Therefore, you can make measurements on the data, and you can turn on or
off digital bandwidth limit or interpolation without having to reacquire the
data. This is important because the real-time sampling mode is primarily
used on events that happen either once or infrequently, and reacquiring the
data may not be one of your options. Also, turning on interpolation usually
improves the repeatability of your measurements.
The equivalent-time sampling mode is slightly different. Notice that
averaging is turned on or off before the data is stored in the channel
memories. That means once the data is acquired, if you need to turn
averaging on or off before making any measurements, you must reacquire the
data. However, because the equivalent-time sampling mode is primarily used
on repetitive signals, you should be able to reacquire the data.
1–9