Transcript POST AND ASSIGNMENT OF SYSTEM RESOURCES

POST AND ASSIGNMENT OF
SYSTEM RESOURCES
FIRST STEP
•
When the power first is turned on, the system clock begins to generate
clock pulses.
SECOND STEP
•
The CPU begins working and initializes itself (resetting its internal
values).
THIRD STEP
• The CPU turns to memory address FFFF0h, which is the memory address
always assigned to the first instruction in the ROM BIOS startup program.
FOURTH STEP
• This instruction directs the CPU to run POST
FIFTH STEP
• POST first checks the BIOS program operating it and then tests CMOS
RAM.
SIXTH STEP
• A test determines that there has been no battery failure.
SEVENTH STEP
• Hardware interrupts are disable. (This means that pressing a key on the
key-board or using another input device at this point does not affect
anything.)
EIGHTH STEP
• Tests are run on the CPU, and it is initialized further.
NINTH STEP
• A check determines if this is a cold boot. If so, the 16KB of RAM is
tested.
TENTH STEP
• Hardware devices installed on the computer are inventoried and compared
to configuration information.
ELEVENTH STEP
• The video card is tested and configured. During POST, before the CPU
has checked the video system, beeps sometimes communicate errors. Short
and long beeps indicate an error; the coding for beeps depends on the
BIOS. After POST checks and verifies the video controller card (note that
POST does not check to see if a monitor is present or working), POST
can use the monitor to display its progress.
TWELFTH STEP
• POST checks RAM by writing and reading data. The monitor displays a
running count of RAM during this phase.
THIRTEENTH STEP
• Next, the keyboard is checked (if you press and hold any keys at this point,
an error occurs with some BIOSs). Secondary storage devices (including
floppy disk drives and hard drives), ports, and other hardware are tested
and configured. The hardware that POST finds is checked against the data
stored in CMOS RAM, jumpers, and/or DIP switches to determine if they
agree. IRQ, I/O addresses, and DMA assignments are made; the OS
completes this process later.
FOURTEENTH STEP
• Some devices are set up to go into sleep mode to conserve electricity.
FIFTEENTH STEP
• The DMA and interrupt controllers are checked.
SIXTEENTH STEP
• CMOS setup is run if requested.
SEVENTEENTH STEP
• BIOS begins its search for an OS.
THE END
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