Thunderbird 1,2GHz en Duron 800MHz overclocking

I refrained from benchmarking Duron 800 at its defined clock frequency, because I have published numbers of Duron 800 already a few months ago and they obviously haven't changed since.[snip] I still did benchmark the Duron 800 sample, but only at 1000 MHz.

. I also overclocked Athlon 1200. You might know from AMD's data sheets, that no current Athlon and Duron processors can be adjusted to a higher clock divider (multiplier) than x12.5. Therefore I was limited to 1250 MHz as long as I stuck to the official 100 MHz bus clock of Athlon. To reach more I had to increase the bus clock and the overclocked Athlon 1200 was 'only' able to finish the touchy Linux kernel compilation successfully at up to 1287 MHz (103 MHz x 12.5).

If you look at the results of Duron 1000 and Athlon 1287 you might notice something very interesting. The benchmark score in the majority of the tests doesn't increase anymore as much as expected. This is particularly obvious in case of Duron at 1 GHz. There's only one explanation for this behavior. A clock multiplier of x9.5 seems to be the sweet spot of Duron and its 64 kB second level cache. Increasing Duron's clock frequency to 10 times the bus clock or more makes the clock difference between bus and processor core too big for Duron's small L2-cache to buffer the supply with code and data from main memory. Basically Duron is simply not getting any faster anymore, because the core is starving for code and data at a core-to-bus-clock ratio of beyond 9.5. The same seems to be valid for Athlon at a multiplier of beyond 12.5, which might be the reason why AMD didn't incorporate any higher multiplier into Athlon's core.

This brings us to the simple conclusion that AMD will need to increase the bus clock in order to get more than 950 MHz out of Duron and more than 1250 MHz out of Athlon. The next Athlon processor will probably be an Athlon 1330, running at 133 MHz bus clock x 10. This could also mean that you will require new platforms for the next batch of Athlons, since I doubt that the current ones are able to support 133 MHz EV6-bus.