How much buffer memory we can create in STM32H747I-DISCO?

[Amelie ACKERMANN]

How much buffer memory we can create in STM32H747I-DISCO?

[Tesla DeLorean]

Buffer for what? At what rates?

The board has internal and external memory. 

32MByte of SDRAM for ADC samples for instance 

Perhaps look at the product page and related documentation?  https://www.st.com/en/evaluation-tools/stm32h747i-disco.html