"You will see in bit 7 really the only new feature of the KT333 chipset and that is the CPU+33=DRAM. The KT266 technically has support built into it for running the asynchronous bus. What I believe VIA did was they either were unable to get this feature working properly by time they wanted to ship their chipset OR they decided they could release a new chipset later on with features that should have been in the previous release. Just think KT133 and KT133a, KT266 and KT266a. Where as the A only brings the benefits that the original SHOULD have brought.
After finding some information on asynch registers in VIA's white papers I thought I'd give this a try. Surprisingly I was able to get both of these settings to work on my Abit KR7a. I've had some other people try this register and it results in an instant lockup. Before you even try this please make sure that your RAM is capable of running 166Mhz with all the timings you have set and give a good amount of room just to be on the safe side. I'm really quite interested in seeing some more peoples results with this."