On ThinkPad W520 systems, users have reported decreased system performance and the lack of Turbo Boost functionality while running on battery (DC) power.
All the following ThinkPad system running on all Operating Systems:
On battery (DC) power, the ThinkPad W520 is designed to put the CPU in Low Frequency Mode, disable Turbo Boost, and scale back the clock speed of the nVidia graphics chip because the overall system power consumption exceeds the available battery supply.
The AC adapter, however, does not have this limitation, and can offer full workstation performance as expected.
In order to get maximum performance from the ThinkPad W520:
Only ThinkPad W520 systems are affected.