AMD Athlon "Thunderbird" 1 GHz / 800 MHz

Overclocking

The Athlon, as well as all Pentium II and early Pentium III CPU's, have been limited in overclocking potential in part by the external L2 Cache chips. When Intel released its first CPU with on-die cache, the Celeron 300A, a new era in overclocking was upon us. No longer was it necessary to worry about cache speeds as that on-die cache scaled with the core clock thanks to it being built using the same process technology as the rest of the core.

Intel did the same for the Coppermine core used on the latest Pentium III's and, as stated earlier, AMD has done the same for the Thunderbird. Does that mean the Thunderbird is an overclocking monster like some of the Celeron and Pentium III models with on-die cache? Well there's a lot more to overclocking than just on-die cache, although the limits of external cache speed has prevented overclockers from pushing their Athlon's to the max.

Overclocking the Athlon in the past was accomplished most easily with a "Gold Finger Device"  that allowed you to adjust the multiplier of any Slot-A Athlon. If you haven't heard the rumors by now, the Thunderbird, as well as all future Socket-A CPUs including the Duron, is multiplier locked, meaning that you cannot adjust the multiplier of the CPU.

Currently, it seems as if AMD is using a technique similar to what Intel has been doing with their processors ever since the release of the Celeron, thus completely locking them.  It is highly unlikely that there will be any way around this, thus limiting the overclocking potential of the new Thunderbirds to what you can do with simply increasing the FSB. 

Traditionally, we've only been able to push the EV6 bus to about 110MHz, whether it be on a KX133 or an AMD 750 based motherboard. Before we even had our CPU's in hand, we know that this was likely to limit the overclocking potential of the Thunderbird. The 8363 North Bridge of the KT133 is very similar to the 8371 used on the KX133 so the maximum attainable FSB speed probably won't change much. The AMD 760, expected later this year, is expected to introduce a 133 MHz DDR (266 MHz effective) version of the EV6 bus and should enable a number of overclocking options for the Thunderbird.

At the time of publiciation, we had two Thunderbird samples to play around with. Running at 1 GHz and 800 MHz meant that we had CPU's with a multiplier of 10X and another with a multiplier of 8X. Motherboard selection was also limited, with about 5 pre-production models available to us. These factors conspired to prevent us from overclocking our Thunderbirds beyond 1.05 GHz and 840 MHz using a 105 MHz FSB speed. Even with such a mild overclock, the systems were not 100% stable under these conditions. The fact that both CPU's topped out at an FSB speed of 105 MHz seems to indicate that there may be hope for the Thunderbird to overclock more than 5% once final boards are available, but only time will tell.