Monday, March 9, 2009

POST Beep Codes

Usually if there is a hardware problem with the PC, it refuses to boot up normally. The common tell-tale signs would be the output screen stays blank.

But such tell-tale signs tell nothing but just an indicator of something is wrong inside the PC.
If your PC is able to power up but unable to show any display on the screen, do look out for another indicator which is audible instead of a visual indicator.

Most mainboard have a boot sequence even before it allows the harddisk to start booting the installed operating system. This boot sequence is controlled by something called the BIOS. The boot sequence itself is known as the POST [ Power On Self Test ].

So the BIOS will check for all installed hardware on the mainboard and ensure that critical components such as RAM,Video display and CPU are installed before going on to check other devices which are of lesser priority [ ie not absolutely necessary for PC to startup ].

Since the BIOS is able to detect the presence of critical and non-critical components, sensing that if there is any critical components missing, the boot sequence will be incomplete. Thus resulting in what most of us experience when the PC cannot boot up. Besides stopping the PC from booting up, the BIOS will also present a set of audible signals to the user. These audible signals come in the form of beeps generated by the internal PC speaker [ usually embedded in the PC casing ].

Though some newer PCs don't come with these internal PC speakers nowadays, most still do have this little speaker that does nothing but generate beeps. To find out if there is such a speaker in the PC, just listen for quick beep whenever a PC is turned on. If you can hear such a beep, it means the PC is equipped with such an internal speaker.

So, the BIOS upon detecting missing critical components it'll generate a sequence of beeps upon completing the POST. For each detected problem, it will generate the beeps in different sequence. The PC owner, knowing the issue faced, can then proceed to troubleshoot the PC in the specific hardware/region as the POST beeps codes has already narrowed down the possible causes to a fewer causes. This then help saves time for troubleshooting whereby the user have to test each and every hardware for problems.

Below is a set of standard beep codes and its detected errors.

If your mainboard is using AMI BIOS[ America Megatrends ]
  • 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)

If your mainboard is using Phoenix BIOS
eg. 1-1-4-1 means the beeping sequence will be *----*----****----*
  • 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
To know if your mainboard is AMI or Phoenix BIOS, it's usually shown on the display as the PC boots before it starts loading the OS.

For more reading, visit Wikipedia page on POST

Today is 9th March 2009
Time now is 08:56 hrs

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