The XSUSB Board attaches to the parallel port connector of the XSA or XSB Board
and converts it into a USB interface.
Then you can use all the XSTOOLs utilities through
a USB port.
This is especially useful for newer laptops which have no parallel port.
And the USB link is much faster - anywhere from 2x to 13x faster on FPGA/SDRAM/Flash downloads and uploads!