Defines how much buffer memory is asigned for each data block. A data block may hold multiple events. This register sets the number of buffers what can be written before the module goes full and acquisition is suspended. 

Select either the number of buffers or the buffer size required - these are not independent options

Normally you should allow the acquisition software to calculate and set this option based on other options such as the data sources enabled and size of the waveform buffers (if enabled).