On ThinkPad W520 systems, users have reported the CPU frequency is capped when Turbo Boost activates while running on AC power.
All the following ThinkPad system running on all Operating Systems:
A new BIOS was released to resolve the CPU frequency capping during Turbo Boost on AC power.
Version 1.26-1.16 (8BET46WW):
In order to get maximum performance from the ThinkPad W520:
Only ThinkPad W520 systems are affected.