The Duron is pin-compatible with the Athlon and virtually indistinguishable from it, operating on the same motherboards in most cases. The only external way to tell is by reading the small text on the core, stating either "Athlon" or "Duron". The Duron has the same 128K of level 1 cache as the Athlon, but only 64K of level 2 cache, as compared to 256K on the more expensive chip. Because of this, the Duron generally lags behind the Athlon on business applications, but keeps up in floating-point operations thanks to its powerful FPU, which is identical to the Athlon's. The original Duron was limited to operating on a 100 MHz front-side bus speed (DDR200), while the Athlon at the time could run on a bus clock of 133 MHz (DDR266). Later Durons supported a 133MHz bus (DDR266).
The original Duron, on the "Spitfire" core, was manufactured in 2000 and 2001 at speeds ranging from 650 to 950 MHz. It was based on the "Thunderbird" Athlon core. The second-generation Duron, the "Morgan" core, is sold in speed grades between 1000 and 1300 MHz, and is based on the Athlon XP "Palomino" core.
In 2003, AMD released several new iterations of the Duron, based on the "Thoroughbred" core, in this case, nicknamed "Applebred". The "Applebred" Duron is availiable in 1.4GHz, 1.6GHz and 1.8GHz forms, all on a 133MHz (DDR266) bus by default. Enthausiast groups have discovered these Durons to be largely rebadged, unmodified, Thoroughbred cores, with some enthausiasts successfully turning their Durons into fullblown Athlon XP's with 256K of L2 cache.
see also: List of AMD microprocessors