POST and Entering Setup
- 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 SETUP.
- 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 explanation.
- Most BIOS POST sequences occur along four stages (five if
you have a PCI bus):
- Display some basic information about the video card like
its brand, video BIOS version and video memory available.
Since the system's BIOS takes over the POST right after
the video card BIOS, you will not have enough time to
read the displayed information.
- 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 BIOS identification line.
- Display memory count. You will also hear tick sounds if
you have enabled it (see Memory Test Tick Sound section).
- If you have a PCI bus, the system will attempt an
initialisation of the cards and will display the card's
name.
- 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
configurations:
- Main Processor: The type of CPU identified by the
BIOS. Usually Cx386DX, Cx486DX, P120, etc..
- 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 ones).
- 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 CMOS Setup).
- 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 and COM2.
- Parallel Port(s): The hex number of your LTP
ports. 378 for LPT1.
- Cache memory 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.
- PCI cards information. If your system
supports PCI cards, you will see a table containing a
list of your PCI cards, as well as its PCI port number (0
to 3 or A to D) and the manufacturer's number.
- 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 the screen. 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 on the
system board has failed to function properly.
- 5 beeps: Processor failure. The CPU on the system
board has generated an error.
- 6 beeps: Keyboard Controller 8042-Gate A20 error.
The keyboard controller (8042) contains the gate A20 switch
which allows the computer to operate in virtual mode.
This error message means that the BIOS is not able to
switch the CPU into protected mode.
- 7 beeps: Virtual Mode (processor) Exception error.
The CPU on the motherboard has generated an Interrupt Failure
exception interrupt.
- 8 beeps: Display Memory R/W Test failure. The
system video adapter is either missing or Read/Write
Error its memory is faulty. This is not a fatal error.
- 9 beeps: ROM-BIOS Checksum failure. The ROM
checksum value does not match the value encoded in the BIOS.
This is good indication that the BIOS ROMs went bad.
- 10 beeps: CMOS Shutdown Register. The shutdown
register for the CMOS memory Read/Write Error has failed.
- 11 beeps: Cache Error / External Cache Bad. The
external cache is faulty.
- 2 short beeps: POST failed. This is caused by a
failure of one of the hardware testing procedures.
- 1 long & 2 short beeps: Video failure. This is
caused by one of two possible hardware faults. 1) Video BIOS
ROM failure, checksum error encountered. 2) The video
adapter installed has a horizontal retrace failure.
- 1 long & 3 short beeps: Video failure. This is
caused by one of three possible hardware problems. 1) The video
DAC has failed. 2) the monitor detection process has
failed. 3) The video RAM has failed.
- 1 long beep: POST successful. This
indicates that all hardware tests were completed without
encountering errors.
- If you have access to a POST Card reader,
(Jameco, etc.) you can watch the system perform each test by
the value that's displayed. If/when the system hangs (if
there's a problem) the last value displayed will give you
a good idea where and what went wrong, or what's bad on
the system board. Of course, having a description of
those codes would be helpful, and different BIOSes have
different meanings for the codes. (could someone point
out FTP sites where we could have access to a complete
list of error codes for different versions of AMI and
Award BIOSes?).
- This is a short list of most frequent on-screen BIOS
error messages. Your system may show them in a different manner.
When you see any of these, you are in trouble - Doh!
(Does someone has any additions or corrections?)
- "8042 Gate - A20 Error": Gate A20 on the
keyboard controller (8042) is not working.
- "Address Line Short!": Error in the
address decoding circuitry.
- "Cache Memory Bad, Do Not Enable Cache!":
Cache memory is defective.
- "CH-2 Timer Error": There is an error in
timer 2. Several systems have two timers.
- "CMOS Battery State Low" : The battery
power is getting low. It would be a good idea to replace
the battery.
- "CMOS Checksum Failure" : After CMOS RAM
values are saved, a checksum value is generated for error
checking. The previous value is different from the
current value.
- "CMOS System Options Not Set": The
values stored in CMOS RAM are either corrupt or
nonexistent.
- "CMOS Display Type Mismatch": The video
type in CMOS RAM is not the one detected by the BIOS.
- "CMOS Memory Size Mismatch": The
physical amount of memory on the motherboard is different
than the amount in CMOS RAM.
- "CMOS Time and Date Not Set": Self
evident.
- "Diskette Boot Failure": The boot disk
in floppy drive A: is corrupted (virus?). Is an operating
system present?
- "Display Switch Not Proper": A video
switch on the motherboard must be set to either color or monochrome.
- "DMA Error": Error in the DMA (Direct
Memory Access) controller.
- "DMA #1 Error": Error in the first DMA
channel.
- "DMA #2 Error": Error in the second DMA
channel.
- "FDD Controller Failure": The BIOS
cannot communicate with the floppy disk drive controller.
- "HDD Controller Failure": The BIOS
cannot communicate with the hard disk drive controller.
- "INTR #1 Error": Interrupt channel 1
failed POST.
- "INTR #2 Error": Interrupt channel 2
failed POST.
- "Keyboard Error": There is a timing
problem with the keyboard.
- "KB/Interface Error": There is an error
in the keyboard connector.
- "Parity Error ????": Parity error in
system memory at an unknown address.
- "Memory Parity Error at xxxxx": Memory
failed at the xxxxx address.
- "I/O Card Parity Error at xxxxx": An
expansion card failed at the xxxxx address.
- "DMA Bus Time-out": A device has used
the bus signal for more than allocated time (around 8 microseconds).
- If you encounter any POST error, there is a
good chance that it is an HARDWARE related problem. You should
at least verify if adaptor cards or other removable
components (simms, drams etc...) are properly inserted before
calling for help. One common attribute in human nature is
to rely on others before investigating the problem yourself.
Please don't be a politician (Aide-toi et le ciel
t'aidera).