BIT file is a binary file genereted by Xilinx software. It contains configuration data and header information used by BitGen. BIT files are used also by other Xilinx tools: iMPACT and PROMGen.

The main purpose of BIT files is generating bitstreams for field-programmable gate arrays (FPGA). FPGA architecture was designed by Xilinx, which supplied its devices for Mars missions (Spirit and Opportunity).