Asus P9X79 WS - Manual (Page 40)

2.2.7 Onboard LEDs
1. Standby Power LEDs
The motherboard comes with a standby power LED that lights up to indicate
that the system is ON, in sleep mode, or in soft-off mode. This is a reminder
that you should shut down the system and unplug the power cable before
removing or plugging in any motherboard component. The illustration below
shows the location of the onboard LED. The Standby Power LEDs will light
up once the system is connected to a power source
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2. Diag. LED
These diagnosis LEDs of CPU, DRAM, VGA card, and HDD indicate
key component status during POST (Power-on Self Test), providing an
elegant embellishment to the motherboard design. The LED lights will flash
sequentially during system bootup. If an error is found, the LED next to the
error device will continue lighting until the problem is solved. This user-
friendly design provides an intuitional way to locate the root problem within a
second.
2-12 Chapter 2: Hardware information