The most significant difference between a Thoroughbred and a Barton is that the Barton core is newer and includes a 512KB L2 cache, as opposed to the 256KB L2 cache of the Thoroughbred. Also, the Barton has support for a 400 MHz/333 MHz FSB as opposed to the 333 MHz/266MHz FSB for the Thoroughbred. The Barton also a larger number of transistors, 55m, as compared to the 37m of the Thoroughbreds. But since AMD adopts a performance based numbering scheme, the performance between an Athlon 2800+ Barton and an Athlon 2800+ Thoroughbred would be very nearly the same, unless you do extensive benchmarks.