有大大知道 記憶體 Pull-Up Level 的意義嗎??

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Driving Strength Profile
Data Driving Pull-Up Level
Cmd Driving Pull-Up Level
Ctrl Driving Pull-Up Level
Clk Driving Pull-Up Level

Data Driving Pull-Down Level
Cmd Driving Pull-Down Level
Ctrl Driving Pull-Down Level
Clk Driving Pull-Down Level

有大大知道上面這些東西的作用跟意義嗎??是在調整什麼東西的??
煩請告知 感激不盡