Thanks T-Break for sending this in.
As T-Break mentioned earlier, the 645DX is basically the 645 chipset supporting
133MHz FSB for the Pentium 4. Thus, there aren't many new features on this chipset- think of it as an "A" version of a VIA chipset which tweaks performance. T-Break did find a couple of new things in the BIOS. Firstly, the BIOS supports DDR-400 as there is an option to configure your memory to DDR-400. However, if you do so, the memory timing are set to lowest such as CAS 2.5 etc.