A chicken bit is an undocumented or engineering-level configuration flag built into a processor or ASIC during the design phase. If a new architectural feature, like a specific branch predictor or cache optimization, causes silicon failures after fabrication, engineers can toggle this bit to bypass the faulty logic. It allows the rest of the chip to function and be sold, albeit with a slight performance penalty.
The new prefetcher is causing a race condition, so just flip the chicken bit in the BIOS to turn it off for this stepping.
Toggling a chicken bit is often the last resort to save a multi-million dollar tape-out when a localized bug is discovered in early silicon.
Related terms
ASIC
An application-specific integrated circuit designed for one dedicated task rather than general-purpose use.
Silicon lottery
The natural variance in manufacturing quality that dictates how far a specific chip can be overclocked.
Firm error
A data or logic fault that persists until the system is rebooted or power-cycled.
Tape out
To finalize an integrated circuit design and send the manufacturing data to the foundry.