The ring buffer mode is the standard mode of all oscilloscope boards. Data is written in a ring memory of the board until a trigger event is detected. After the event the posttrigger values are recorded. Because of this continuously recording in a ring buffer there are also samples prior to the trigger event visible: Pretrigger = Memsize - Posttrigger.
When using M2i or M3i cards it is possible to start readout of memory as soon as the trigger has been recognized. With this feature data is far earlier available for further work and the repitition rate is increased.