For the more advanced power users this is nothing new, but for the less techy it might be good to highlight the CPU microcode. Without making things too technical, the CPU microcode ("µCode") is a small piece of software that the hardware manufacturer (Intel, AMD, Nvidia) write to achieve optimal performance at hardware-level. As with any software, sometimes there are performance problems that can be solved via the CPU µCode. Usually you will not notice any of the errata (= problems) during your daily computing experience, but sometimes it happens. For example, remember the famous TLB-bug on the first generation of Phenom B2 stepping processors. That bug was first solved with a µCode patch and later included in the B3 revision. Microcode can be used to resolve or work around hardware problems.
It is also possible that new µCode brings slower performance for legacy software. For example, for optimal SuperPI 1M performance using an Intel Core 2 processor, we were all using an old version of the µCode.
Coming back to the AMD story, The Stilt (who else?) compiled a list of the AGESA code (AMD µCode) versions for most of the 970/990 AMD motherboards. If you are using the Bulldozer patch for better SuperPI 1M/32M results, you might want to know what AGESA version you are using! It is possible that since this list, there has been BIOS releases with the latest AGESA code. ASRock already published a beta version for their 990FX Extreme9 motherboard. If you find any other fixed BIOSes, please drop a message in the forum.
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