The Red LED will light up when VCore booster is pressed. When one Red LED is lit, VCore is boosted by +0.v. When 2 Red LEDs are lit, VCore is boosted by +0.2v. To stop the VCore boost, just press again and VCore will go down to what you have set. The 2 buttons are exactly the same in function each.

Vtt Booster

The far right button on the EVGA ECP increases the VTT voltage by +0.1v.

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EVGA P55 FTW manual Vtt Booster