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The Power On Self Test
When the system is powered on, the BIOS will perform diagnostics and initialize
system components, including the video system. (This is self-evident when the
screen first flicks before the Video Card header is displayed). This is commonly
referred as POST (Power-On Self Test).
Afterwards, the computer will proceed its final boot-up stage by calling the
operating system. Just before that, the user may interrupt to have access to
To allow the user to alter the CMOS settings, the BIOS provides a little program,
SETUP. Usually, setup can be entered by pressing a special key combination (DEL,
ESC, CTRL-ESC, or CRTL-ALT-ESC) at boot time (Some BIOSes allow you to enter
setup at any time by pressing CTRL-ALT-ESC). The AMI BIOS is mostly entered by
pressing the DEL key after resetting (CTRL-ALT-DEL) or powering up the computer.
You can bypass the extended CMOS settings by holding the <INS> key down during
boot-up. This is really helpful, especially if you bend the CMOS settings right
out of shape and the computer won\'t boot properly anymore. This is also a handy
tip for people who play with the older AMI BIOSes with the XCMOS setup. It
allows changes directly to the chip registers with very little technical
A Typical BIOS POST Sequence
Most BIOS POST sequences occur along four stages:
1. Display some basic information about the video card like its brand,
video BIOS version and video memory available.
2. Display the BIOS version and copyright notice in upper middle screen.
You will see a large sequence of numbers at the bottom of the screen. This
sequence is the .
3. Display memory count. You will also hear tick sounds if you have enabled
it (see Memory Test Tick Sound section).
4. Once the POST have succeeded and the BIOS is ready to call the operating
system (DOS, OS/2, NT, WIN95, etc.) you will see a basic table of the system\'s
· Main Processor: The type of CPU identified by the BIOS. Usually Cx386DX,
· Numeric Processor: Present if you have a FPU or None on the contrary. If
you have a FPU and the BIOS does not recognize it, see section Numeric Processor
Test in Advanced CMOS Setup.
· Floppy Drive A: The drive A type. See section Floppy drive A in Standard
CMOS Setup to alter this setting.
· Floppy Drive B: Idem.
· Display Type: See section Primary display in Standard CMOS Setup.
· AMI or Award BIOS Date: The revision date of your BIOS. Useful to
mention when you have compatibility problems with adaptor cards (notably fancy
· Base Memory Size: The number of KB of base memory. Usually 640.
· Ext. Memory Size: The number of KB of extended memory.
In the majority of cases, the summation of base memory and extended memory does
not equal the total system memory.
For instance in a 4096 KB (4MB) system, you will have 640KB of base memory and
3072KB of extended memory, a total of 3712KB.
The missing 384KB is reserved by the BIOS, mainly as shadow memory (see Advanced
· Hard Disk C: Type: The master HDD number. See Hard disk C: type section
in Standard CMOS Setup.
· Hard Disk D: Type: The slave HDD number. See Hard disk D: type section
in Standard CMOS Setup.
· Serial Port(s): The hex numbers of your COM ports. 3F8 and 2F8 for COM1
· Parallel Port(s): The hex number of your LTP ports. 378 for LPT1.
· Other information: Right under the table, BIOS usually displays the size
of cache memory.
Common sizes are 64KB, 128KB or 256KB. See External Cache Memory section in
Advanced CMOS Setup.
AMI BIOS POST Errors
During the POST routines, which are performed each time the system is powered on,
errors may occur. Non-fatal errors are those which, in most cases, allow the
system to continue the boot up process. The error messages normally appear on
Fatal errors are those which will not allow the system to continue the boot-up
procedure. If a fatal error occurs, you should consult with your system
manufacturer or dealer for possible repairs. These errors are usually
communicated through a series of audible beeps. The numbers on the fatal error
list correspond to the number of beeps for the corresponding error. All errors
listed, with the exception of #8, are fatal errors. All errors found by the BIOS
will be forwarded to the I/O port 80h.
· 1 beep: DRAM refresh failure. The memory refresh circuitry on the
motherboard is faulty.
· 2 beeps: Parity Circuit failure. A parity error was detected in the base
memory (first 64k Block) of the system.
· 3 beeps: Base 64K RAM failure. A memory failure occurred within the
first 64k of memory.
· 4 beeps: System Timer failure. Timer #1
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BIOS, Power-on self-test, American Megatrends, Motherboard, POST card, Booting, Nonvolatile BIOS memory, Dynamic random-access memory, Error message, Floppy disk, BIOS interrupt call, IBM Personal ComputerAT
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