"A VIA spokesperson would not confirm nor deny that this was a problem, however he did emphasize that the KX133 was specifically designed for the K-75, and that at the time it was developed the 1GHz+ processors were still thought to be over a year away. An AMD spokesperson would not provide any specifics about the reason for the incompatibility, but said it was 'not surprising' that a chipset designed a year ago for the K-75 would have some compatibility issues with the Thunderbird. After doing a bit of digging, it appears that the problem is actually the same issue that may prevent the development of cost effective Slot A to Socket A converters (Slockets). It seems that some of the necessary timings for higher frequency Athlons (the address bus hold time has been specifically mentioned) were not known nor anticipated by VIA in their development of this chipset, so the KX133 timings are just outside of what the Thunderbird requires. Trace length is always an important consideration in regards to timings, so it is entirely possible that some good motherboard designs will actually work with Slot A Thunderbirds. For most people, however, this isn't really much of a consolation, since AMD does not plan on putting any Slot A Athlons in the channel, as they are intended only for OEMs.<P>The focus is now going to be on the KZ133 chipset, which, as reported last month, has been 'tuned' for the Socket A processors. The VIA spokesperson indicated that while both the KX133 and KZ133 are electrically compatible, the pin locations are slightly different so that trace lengths can be kept as short as possible for each type of processor connector. Though some have criticized AMD (and Intel) for going back to a socketed connector for the CPU, both companies have said that higher frequencies require shorter traces, which a socket allows for. Of course, with on-die caches now standard, there is really no reason to mount the processor on a card anymore, so cost is a big consideration too.<P>It is well known that KZ133 will support the 133MHz bus speed, as well as all of the other features of the KX133, however it also appears that it will include ATA/100 support. It also seems likely that some of the critical timings will be addressed before the official release (no pun intended), if they have not already done so. One upside to this is that a Socket A motherboard will support both the Duron and the Thunderbird, allowing for a relatively inexpensive upgrade today, and a potentially excellent upgrade path in the future." - Dean Kent.