When a PC is first switched on or reset it performs a special diagnostic test called a POST (Power-On Self Test), to check all of the components in the PC the POST program sends out a signal to each device initialising each device's built-in self test procedure.
The POST test is a two stage process, first it will check all of the basic components including amongst other things the system clock, the processor, RAM, the keyboard controller and the Video Card.

When a device fails the first part of the POST, the BIOS will send a series of beeps from the PC's speaker (internal) to inform the PC user that there is a problem, these beeps are coded allowing the user to diagnose the troublesome component.

After the video has been tested the BIOS will then indicate any errors encountered by displaying either a numeric code or a text message on the screen.

When the POST has been completed successfully the PC will make a short beep to let the user know everything is as it should be.

elow are some common beep codes for AMI and Phoenix BIOS.

AMI BIOS ERROR BEEP CODES

• 1 Beep - Memory Refresh Failure (check memory)
• 2 Beeps - Memory Parity Error in first 64KB block (check memory)
• 3 Beeps - Memory Read/Write Error in first 64KB block (check memory)
• 4 Beeps - Motherboard timer not functioning (possible motherboard replacement)
• 5 Beeps - Processor Error (may need replacement Processor)
• 6 Beeps - Gate A20/keyboard controller failure (possible motherboard replacement)
• 7 Beeps - Processor Exception Interrupt Error (may need replacement Processor)
• 8 Beeps - Display Memory Read/Write Failure (reseat or replace video card)
• 9 Beeps - ROM checksum Error (replace BIOS chip or motherboard)
• 10 Beeps - CMOS shutdown Read/Write error (possible motherboard replacement)
• 11 Beeps - Bad Cache Memory - test failed (replace cache memory)

Phoenix BIOS ERROR BEEP CODES

• 1-1-4-1 - Cache Error (level 2)
• 1-2-2-3 - BIOS ROM Checksum
• 1-3-1-1 - DRAM Refresh Test
• 1-3-1-3 - Keyboard controller test
• 1-3-4-1 - RAM Failure on address line xxxx (check memory)
• 1-3-4-3 - RAM Failure on data bits xxxx of low byte of memory bus
• 1-4-1-1 - RAM Failure on data bits xxxx of high byte of memory bus
• 2-1-2-3 - ROM copyright notice
• 2-2-3-1 - Test for unexpected interrupts

AWARD BIOS ERROR BEEP CODES

• one long beep and two short beeps - Video error (reseat or replace video card)
• two short beeps - Non-Fatal Error (reseat RAM, check other components)

• AMI BIOS
• Phoenix/Award BIOS