Datasheet

Chapter 3: System Interface
3-3
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Power: Indicates power is being supplied to the system's power
supply units. This LED should normally be illuminated when the system is
operating.
3-4 Serial ATA Drive Carrier LEDs
On the front of each Serial ATA drive carrier is a green LED. When illuminated,
it indicates drive activity. A connection to the Serial ATA backplane enables this
LED to blink on and off when that particular drive is being accessed.