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The POST Process
1. A user powers the system on through the power button.
2. A signal passes through the system board to the processor.
3. The processor interprets the signal and in turn, signals the soft‐switched power supply to power up
the system.
4. The power supply sends an electrical current to all of its power leads.
Function of the BIOS in the POST Process
The functions of the BIOS in the POST process are:
•
The BIOS initializes the core chipsets.
•
The BIOS checks and configures the memory.
•
The BIOS enables L1 and L2 caches and checks the processor.
•
The BIOS copies itself into the memory and passes control to the copy in memory.
NOTE: The Extended System Configuration Data (ESCD) set stores information about Plug‐and‐Play
devices. The BIOS and some operating systems access ESCD each time you reboot your computer. This
memory is also referred to as NVRAM.
The BIOS runs another memory check before moving onto the keyboard test.
•
The BIOS tests the keyboard, during which the LEDs should flash.
•
The BIOS tests and initializes the video, which can be witnessed from the splash screen.
•
The BIOS verifies the resource assignments in ESCD and reallocates resources if new hardware is
found. This test may be bypassed if PnP OS is enabled. Enabling PnP OS causes resource assignments
to be handled by the operating system.
•
Any ROM chips such as a NIC or SCSI controller initialize and Dell Power Management starts up. The
BIOS checks for a system password, and then passes control to the operating system.
Troubleshooting Power‐or POST‐Related Stage Failures
Before troubleshooting any power‐ or POST‐related issues, isolate the notebook. Remove it from any
docking station or port replicator. Disconnect any external power supply and check the status of the
battery.
When troubleshooting a power‐ or POST‐related stage failure on a notebook, your first task is to classify
the category into which it falls. Is it a power issue or a POST issue? To
do so:
1. Determine if the system is receiving power. Check the system
power LED and the AC adapter for LED activity.
2. Check for any diagnostic LED codes. These codes are a function of
the BIOS and can help determine the process that failed.
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