Performance + Time = Memory (Cost Saving with 3-D Design)(WP273) - Operating logic at a higher rate than the processing rate allows operations to be achieved sequentially. As with a processor, logic is timeshared over multiple clock cycles. Memory holds values not being used on a given clock cycle. The FPGA can be considered to be a three-dimensional volume to be filled. "Performance + Time = Memory" is a strange formula, but when understood, it can often result in significantly lower cost implementations with Xilinx devices.