Understand Field Programmable Gate Arrays.

Field Programmable Gate Arrays (FPGA) are silicon chips manufactured using the same processes as Application Specific Integrated Circuits (ASIC), but where the logic elements can be programmed and re-programmed rather than being defined during manufacturing, as is the case for ASICs.

Typically, an ASIC semiconductor chip is manufactured in several "layers". The layers define logical elements used to implement functions on a chip and are normally "fixed" or fully defined during manufacture. This means that the chip designer must consider how all of the logical elements must be combined to implement the functions he requires. Only when the chip is manufactured can he be sure that these functions operate correctly. If the functions are not performing correctly, a new chip needs to be manufactured.

FPGAs, on the other hand, allow some of the layers to be programmed. This means that the chip designer can define how logical elements should be combined in software, download this "image file" to the FPGA chip and then test whether the intended functions are operating correctly. If not, the designer merely changes the image file, downloads the file to the FPGA chip and re-tests.

For detailed information on FPGAs, manufacturers and other useful links see: http://en.wikipedia.org/wiki/FPGA