>  "What at first sight distinguishes the new [Xilinx] circuits from other
>   programmable logic circuits is probably the flash technology. Xilinx
>   has chosen to use the somewhat more complex, but more compact flash
>   technology instead of EEPROM or RAM technology.
>
>   Since we wanted to program and erase in circuit, EPROM cells was not
>   an alternative, says Scott Lewis. In the choice between flash cells and
>   EEPROM cells, there was no question it must be flash cells. One
>   important reason is that all semiconductor fabs are going for flash
>   processes, and this will press down the price in the long run. Another
>   reason is that flash cells are easy to scale down when changing to
>   more modern technology.
>
>   Xilinx and Seiko-Epson have together developed the new flash process
>   that is used in the new circuits. In the first stage, it is a 0.6 um
>   CMOS process with two metal layers and two polysilicon layers.
>
>   Flash cells are always much smaller than EEPROM cells. Instead of four
>   transistors, one is enough. Xilinx has chosen to sacrifice some area
>   in order to improve reliability. They use two transistors per cell,
>   but are still able to reduce the size to about a third of an EEPROM
>   cell.
>
>   Another advantage with flash cells is that they can be reprogrammed
>   more times than EEPROM cells. The fast flash cells can be reprogrammed
>   10,000 times, and the reprogramming cycle is also short, only 10-100
>   us."