Both.
Alta Mil-Std-1553 and ARINC-429 products use volatile RAM at 1Mbyte per channel (or Bank for ARINC) in addition to a FLASH memory part on each product for storing the firmware (FPGA load).
The document here Letter of Volatility (LOV) for Alta Interface Devices (7578 downloads ) describes Alta products’ non-volatile memory usage, as well as user accessibility to this non-volatile area and safeguard measures for security purposes.