We have been following the story of a chip-level problem in AMD's quad-core Opteron and Phenom processors all week. This bug--CPU makers prefer to call them errata--can cause system hangs in specific, rare circumstances. This sort of obscure problem is not really uncommon in microprocessors, but CPU makers are often able to fix them on the fly with little impact to the end user. This particular erratum is especially unfortunate because the fix for it involves sacrificing a substantial amount of performance.

This week's developments have included the revelation that this bug affects all "Barcelona" quad-core Opterons, leading to a "stop ship" order on quad-core Opterons to most customers. The erratum also affects all speed grades of Phenom processors, which are still shipping to PC makers and resellers. AMD admitted the presence of the erratum prior to the Phenom's public introduction, but the firm's initial statements gave many the impression that the erratum affected only the 2.4GHz version of the Phenom, which it had decided to delay. In truth, all current Phenom variants have the bug, and systems with those processors will have to be patched and suffer the accompanying performance penalty.

One thing we haven't known is exactly how that performance penalty would look--until today. We can now offer you some preliminary benchmarks that demonstrate the impact of the BIOS-based workaround for the problem.