The FPGA "personality" (bitstream configuration file) determines how the RT target interacts with peripheral devices. The personality can also implement custom functionality.
The FPGA bitstream configuration file (“personality”) implements the connection between the RT target and external peripherals, and can also implement hardware functions used by the RT target such as timers. NI offers one standard personality for the NI ELVIS III and two standard personalities (default and high-throughput) for all others which you can use as-is or modify as needed. You can also create a completely custom FPGA personality.
Use the Academic RIO Device Toolkit to develop complete applications by writing code exclusively for the RT target, and use Express VIs to access the wide variety of I/O devices implemented by the default Academic RIO Device FPGA personality.
NI High-Throughput Add-on for myRIO (http://www.ni.com/tutorial/52864/en/)
From the overview: "The myRIO High Throughput Add-on for myRIO is an alternative to the Default FPGA personality that is part of the LabVIEW myRIO Toolkit. It is ideal for projects that require high-speed analog and digital input and output, and is used and accessed similarly to the default FPGA personality. The High Throughput personality offers user-configurable buffered I/O, as well as some of the functionality offered in the Default Personality".