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Introduction to BIOS
BIOS ("Basic Input/Output System" is an essential component in computers, which is used for controlling hardware. It is a small software program, part of which is loaded in ROM (read-only memory, which cannot be modified), and part of which is in EEPROM (electrically erasable programmable read-only memory).
The POST
When a computer system is turned on or reset, the BIOS does an inventory of the hardware found on the computer and carries out a test (called POST for "Power-On Self Test") in order to verify that all of it is functioning properly.
- Testing the processor (CPU)
- Checking the BIOS
- Checking CMOS configuration
- Initialising the timer (the internal clock)
- Initialising the DMA controller
- Checking RAM and cache memory
- Installing all BIOS functions
- Checking all configurations (such as the keyboard, disk drives, and hard drives)
If the POST discovers an error, it will attempt to continue booting the computer. However, if the error is serious, the BIOS will stop loading the system and:
- display a message on the screen, if possible (as the display device might not yet have been initialised, or might be defective);
- emit a sequence of beeps, which refer to the source of the error;
- send a code (called the POST code) to the computer's serial port, which may be retrieved using special diagnostic hardware.
If everything is correct, the BIOS will usually play a short beep to report that there are no errors.
| Meaning of beeps in recent Award BIOS systems | ||
|---|---|---|
| # of beeps | Meaning | How to resolve the problem |
| 1 short beep | PC is booting normally | |
| 2 short beeps | CMOS problem | Reinitialise the CMOS by removing the BIOS stack and replacing it, or by moving jumper JP4 |
| 1 long beep / 1 short beep | Problem with motherboard or RAM | Place RAM modules correctly in slot, test RAM or change it |
| 1 long beep / 2 short beeps | Problem with graphics card | Check that the graphics card is correctly placed in its slot. If need be, test with another video card. |
| 1 long beep / 3 short beeps | Problem with keyboard | Check that the keyboard is correctly plugged in, and that no keys are depressed. If need be, test with another keyboard. |
| 1 long beep / 9 short beeps | BIOS failure | The BIOS is invalid, replace it with a more recent version |
| 3 beeps | Base 64K RAM failure | RAM contains errors. Try reinserting it correctly or replacing it. |
| 4 beeps | Refresh error | RAM is not refreshing correctly. Reset the refresh values in the BIOS or reset the BIOS. |
| 5 beeps | Processor error | Check that the processor is correctly plugged in, and that the fan is working. If need be, change it. |
| 6 beeps | Problem with keyboard | Check that the keyboard is correctly plugged in, and that no keys are depressed. If need be, test with another keyboard. |
| 8 beeps | Problem with graphics card | Check that the graphics card is correctly placed in its slot. If need be, test with another video card. |
| Long incessant beeps | RAM error | Place RAM modules correctly in slot, test RAM or change it |
| Short incessant beeps | Power supply error | Check that all power cables are correctly connected to the motherboard, test with another power supply, or change them |
| Meaning of beeps for an AMI BIOS | ||
|---|---|---|
| # of beeps | Meaning | How to resolve the problem |
| 1 | Refresh failure | RAM is not refreshing correctly. Reset the refresh values in the BIOS or reset the BIOS. Place RAM modules correctly in slot, or change them. |
| 2 | Parity Error | Place RAM modules correctly in slot, or change them. Test the RAM. |
| 3 | Base 64K RAM failure | Place RAM modules correctly in slot, or change them. If need be, update the BIOS. |
| 4 | System timer not operational | The motherboard must be sent for repairs. |
| 5 | Processor Error | Check that the processor is correctly plugged in, and that the fan is working. If need be, change it. |
| 6 | Gate A20 failure | Check that the keyboard is correctly plugged in, and that no keys are depressed. If need be, test with another keyboard. |
| 7 | Processor exception interrupt error | The motherboard must be sent for repairs. |
| 8 | Display memory read/write failure | Check that the graphics card is correctly placed in its slot. If need be, test with another video card. |
| 9 | ROM checksum error | The BIOS chip must be replaced or updated. |
| 10 | CMOS shutdown register read/write error | The motherboard must be sent for repairs. |
| 11 | Cache memory problem | Check that the processor is correctly plugged in, and that the fan is working. If need be, change it. Place the RAM modules correctly in their slots, or replace them. |
| Meaning of beeps in a Phoenix BIOS | ||
|---|---|---|
| # of beeps | Meaning | How to resolve the problem |
| 1-3-1-1 | DRAM Refresh error | Place the RAM modules correctly in their slots, or replace them. |
| 1-2-2-3 | ROM checksum error | Place the RAM modules correctly in their slots, or replace them. |
| 1-3-1-3 | Keyboard Controller Error | Place the keyboard correctly in its slot, or replace it. |
| 1-3-4-1 | RAM error | Place the RAM modules correctly in their slots, or replace them. |
| 1-3-4-3 | RAM error | Place the RAM modules correctly in their slots, or replace them. |
| 1-4-1-1 | RAM error | Place the RAM modules correctly in their slots, or replace them. |
| 2-2-3-1 | Unexpected interrupt | |
 |
It is strongly recommended to shut off the computer's power before making these changes. Whenever doing so, refer to the manual that came with your motherboard. |
Last update on Thursday October 16, 2008 02:43:12 PM.