Thunderbird on KA7
Shortly after the Thunderbirds came out, there was a lot of jumping up and down in relation to getting them working with VIA's KX133 chipset. The KX133 had brought with it a wealth of useful features and some great motherboards had been made around it. However, AMD announced that there was a timing incompatability between KX133 and the new Thunderbird chips, and that these new chips should only be used with motherboards utilizing their own older 750 chipset. To say this caused a lot of angst in the hardware community is an understatement.. :)

However, all is not lost. Yes, on a lot of motherboards you will have reliability problems.. these can range from simply dropping out of 3D applications right up to not even powering up properly, especially when trying to overclock via the FSB. However, there are some KX133-based motherboards that address this timing problem, and one of them is Abit's KA7. In the later BIOSES (I'm using RY), you can change the "CPU Pull Up Strength" and "CPU Drive Strength". The default is 3 and 2, respectively, and these settings work fine for "A" and "C" Athlons. Trying to get a straight answer as to what settings work best with Thunderbirds is an exercise in itself. For example.. Abit recommend 0/1 in their newsgroup messages, DansData had best results with 2/4 and I've had at least 2 reports of it working at the default 3/2. Well, to be completely different, I had the best results at 0/0. 0/1 would result in the machine hanging in about 50% of POSTs, just before booting. 0/0 works rock-stable, as you can see from the benchmarks on the previous page at 115MHz FSB. This needed a voltage boost to 1.85v. However, much to my surprise, I was able to get the TBird to boot and run stably at 124MHz FSB:

I could even get it to partially boot at 127MHz FSB and even POST at 133MHz FSB / 44MHz PCI! However, my video card and hard disk were seriously failing to cope with the high AGP/PCI speeds, hence the benchmarking at 115MHz FSB. Above 120MHz it will occasionally fail to start, but pressing the reset button gets it going again.

Still, this is a lot BETTER than I have been able to do with either of the Classic Athlons. The best, my 950-cored 750 'A' model, is flaky at 120MHz and really only does 115MHz completely stably. This would seem to completely counter the many reports I've seen of Thunderbirds being less overclockable than Classic Athlons on KX133 boards. Maybe I'm just lucky.

Conclusions
Well, those SlotA motherboard owners who feel they're being deal a bad card with the Thunderbird might want to give it a second look. Yes, the results are flaky, but clearly it IS possible to get good things happening with certain combinations of boards and chips. If you've got an older Athlon and are itching for an upgrade but don't want to get a new motherboard, it's certainly worth checking for a later revision of your motherboard's BIOS to see if similar timing options are available. If you can borrow a friend's Tbird or loan one from a shop to see if you can get the stability issues worked out, you may just have a pleasant surprise. However, in all seriousness, you probably want to have a think about how much more you want to invest in SlotA hardware with AMD's current move towards SocketA. Hopefully someone will work out the problems with SlotA<->SocketA adapters and make this problem go away!

CPU's, motherboards and other goodies are all available online in Oz from www.eyo.com.au, shipping Australia-wide from Sydney. Many thanks to Manaz for the loan of his "C" Athlon for this article.