The reason why the Bartons were locked was because AMD wanted to increase sales for their FX line which still remains unlocked. Another reason that I have heard of was, computers would be sold with lower model Bartons (2500+) overclocked and sold as a higher model, which isn’t right.
The following models have been locked (Barton & Thouroughbreds):
AQZFA 0335 MPMW
AQZEA 0338
AQXCA 0340
AQXEA 0341 MPMW and VPMW
AQXFA 0339
AQXFA 0340 MPMW
AQYFA 0340 TPMW and UPAW and WPAW
AQYFA 0341 TPMW
AQYFA 0342
AQZEA 0341 TPMW and RPMW and RPDW
AQZFA 0339 UPMW and TPMW
AQZFA 0340 XPMW
AQZFA 0341 TPMW and SPMW and XPMW
AQZFA 0342 TPMW and UPMW
AQZFA 0341 VPMW
AQZFA 0347 XPMW
Thoroughbred JIXIB 0339
Thoroughbred AIXHB 0340 UPMW
Thoroughbred AIXHB 0341 SPMW
The following models are still unlocked:
AQXFA 0340 MPMW and TPMW and UPMW and VPMW
AQYFA 0340 UPAW
AQZEA 0339 UPMW
AQZFA 0339 VMPW
AQZFA 0339 UMPW
AQZFA 0340 UPMW and SPMW and MPMW
AQZFA 0342 TPMW and UPMW
Thanks to Harris Walktin from
http://www.hardwareanalysis.com/ fourm for this information.