The computer POST

The computer POST (Power On Self Test) tests the computer insuring that it meets the necessary system requirements before booting up. If the computer fails the POST, the computer then returns a beep code indicating what is causing the computer not to pass the POST. Generally, if the computer POST's properly, you will receive a single beep (with some computer BIOS manufacturers, it may beep twice).

Each time the computer boots up, the computer must past the POST. The following is a general procedure of the POST:

If the computer does not pass any of the above tests, your computer will receive an irregular POST. An irregular POST is a beep code which is different from the standard which can be either no beeps at all or a combination of different beeps indicating what is causing the computer not to past the POST.

The following are IBM BIOS Beep Codes that can occur. However, because of the wide variety of models shipping with this BIOS the beep codes may vary.

The following are AMI BIOS Beep Codes that can occur. Again, because of the wide variety of different computer manufacturers with this BIOS the beep codes may vary.

The following are Award BIOS Beep Codes that can occur. Still again, because of the wide variety of different computer manufacturers with this BIOS the beep codes may vary.

Beep Code	Description / What to Check
1-1-1-3	Verify Real Mode
1-1-2-1	Get CPU type
1-1-2-3	Initialize system hardware
1-1-3-1	Initialize chipset registers with initial POST values
1-1-3-2	Set in POST flag
1-1-3-3	Initialize CPU registers
1-1-4-1	Initialize cache to initial POST values
1-1-4-3	Initialize I/O
1-2-1-1	Initialize Power Management
1-2-1-2	Load alternate registers with initial POST values
1-2-1-3	Jump to UserPatch0
1-2-2-1	Initialize keyboard controller
1-2-2-3	BIOS ROM checksum
1-2-3-1	8254 timer initialization
1-2-3-3	8237 DMA controller initialization
1-2-4-1	Reset Programmable Interrupt Controller
1-3-1-1	Test DRAM refresh
1-3-1-3	Test 8742 Keyboard Controller
1-3-2-1	Set ES segment to register to 4 GB
1-3-3-1	28 Autosize DRAM
1-3-3-3	Clear 512K base RAM
1-3-4-1	Test 512 base address lines
1-3-4-3	Test 512K base memory
1-4-1-3	Test CPU bus-clock frequency
1-4-2-4	Reinitialize the chipset
1-4-3-1	Shadow system BIOS ROM
1-4-3-2	Reinitialize the cache
1-4-3-3	Autosize cache
1-4-4-1	Configure advanced chipset registers
1-4-4-2	Load alternate registers with CMOS values
2-1-1-1	Set Initial CPU speed
2-1-1-3	Initialize interrupt vectors
2-1-2-1	Initialize BIOS interrupts
2-1-2-3	Check ROM copyright notice
2-1-2-4	Initialize manager for PCI Options ROMs
2-1-3-1	Check video configuration against CMOS
2-1-3-2	Initialize PCI bus and devices
2-1-3-3	Initialize all video adapters in system
2-1-4-1	Shadow video BIOS ROM
2-1-4-3	Display copyright notice
2-2-1-1	Display CPU type and speed
2-2-1-3	Test keyboard
2-2-2-1	Set key click if enabled
2-2-2-3	56 Enable keyboard
2-2-3-1	Test for unexpected interrupts
2-2-3-3	Display prompt "Press F2 to enter SETUP"
2-2-4-1	Test RAM between 512 and 640k
2-3-1-1	Test expanded memory
2-3-1-3	Test extended memory address lines
2-3-2-1	Jump to UserPatch1
2-3-2-3	Configure advanced cache registers
2-3-3-1	Enable external and CPU caches
2-3-3-3	Display external cache size
2-3-4-1	Display shadow message
2-3-4-3	Display non-disposable segments
2-4-1-1	Display error messages
2-4-1-3	Check for configuration errors
2-4-2-1	Test real-time clock
2-4-2-3	Check for keyboard errors
2-4-4-1	Set up hardware interrupts vectors
2-4-4-3	Test coprocessor if present
3-1-1-1	Disable onboard I/O ports
3-1-1-3	Detect and install external RS232 ports
3-1-2-1	Detect and install external parallel ports
3-1-2-3	Re-initialize onboard I/O ports
3-1-3-1	Initialize BIOS Data Area
3-1-3-3	Initialize Extended BIOS Data Area
3-1-4-1	Initialize floppy controller
3-2-1-1	Initialize hard-disk controller
3-2-1-2	Initialize local-bus hard-disk controller
3-2-1-3	Jump to UserPatch2
3-2-2-1	Disable A20 address line
3-2-2-3	Clear huge ES segment register
3-2-3-1	Search for option ROMs
3-2-3-3	Shadow option ROMs
3-2-4-1	Set up Power Management
3-2-4-3	Enable hardware interrupts
3-3-1-1	Set time of day
3-3-1-3	Check key lock
3-3-3-1	Erase F2 prompt
3-3-3-3	Scan for F2 key stroke
3-3-4-1	Enter SETUP
3-3-4-3	Clear in-POST flag
3-4-1-1	Check for errors
3-4-1-3	POST done--prepare to boot operating system
3-4-2-1	One beep
3-4-2-3	Check password (optional)
3-4-3-1	Clear global descriptor table
3-4-4-1	Clear parity checkers
3-4-4-3	Clear screen (optional)
3-4-4-4	Check virus and backup reminders
4-1-1-1	Try to boot with INT 19
4-2-1-1	Interrupt handler error
4-2-1-3	Unknown interrupt error
4-2-2-1	Pending interrupt error
4-2-2-3	Initialize option ROM error
4-2-3-1	Shutdown error
4-2-3-3	Extended Block Move
4-2-4-1	Shutdown 10 error
4-3-1-3	Initialize the chipset
4-3-1-4	Initialize refresh counter
4-3-2-1	Check for Forced Flash
4-3-2-2	Check HW status of ROM
4-3-2-3	BIOS ROM is OK
4-3-2-4	Do a complete RAM test
4-3-3-1	Do OEM initialization
4-3-3-2	Initialize interrupt controller
4-3-3-3	Read in bootstrap code
4-3-3-4	Initialize all vectors
4-3-4-1	Boot the Flash program
4-3-4-2	Initialize the boot device
4-3-4-3	Boot code was read OK

During the computers boot process the computer performs a POST, which is a test that is performed each time a PC computer is booted up. If the computer passes, you will receive a normal post which in most cases is the computer beeping one or two times. However, in some cases you may receive NO POST or an irregular post indicating something is causing the computer not to pass the test. Below is a listing of some of the general steps that can be performed in helping the computer pass the POST sequence.

Precaution: Some of the following steps recommend removing physical parts within the computer. While working inside the computer, it is highly recommend that you be aware of ESD (ElectricStatic Discharge) and it's potential hazards.

The internal links of this section go to the www.computerhope.com glossary section.

When a personal computer is first turned on, the BIOS tests and configures various components to ensure that they are operating correctly. This operation is called POST (power-on self test). If the BIOS detects any problems during this testing phase, it will attempt to continue to start the computer. However, if the problems are severe, the BIOS may be forced to halt the system.

The following messages are examples of messages including errors detected by the BIOS during POST and a description of what they mean and/or what you may do to correct the error.

	*How Do I Do That?*
Home	Contact Info	How Do I Do That?	The Floppy Disk
	Rants	Surf Report

Beep Code	Description
No Beeps	No Power, Loose Card, or Short
1 Short Beep	Normal POST, computer is OK
2 Short Beep	POST error, review screen for error code
Continuous Beep	No Power, Loose Card, or Short
Repeating Short Beep	No Power, Loose Card, or Short
One Long and One Short Beep	Motherboard issue
One Long and Two short Beeps	Video (Mono/CGA Display Circuitry) issue
One Long and Three Short Beeps.	Video (EGA) Display Circuitry
Three Long Beeps	Keyboard / Keyboard Card error
One Beep, Blank or Incorrect Display	Video Display Circuitry

Beep Code	Descriptions
1 short	DRAM refresh failure
2 short	Parity circuit failure
3 short	Base 64K RAM failure
4 short	System timer failure
5 short	Process failure
6 short	Keyboard controller Gate A20 error
7 short	Virtual mode exception error
8 short	Display memory Read/Write test failure
9 short	ROM BIOS checksum failure
10 short	CMOS shutdown Read/Write error
11 short	Cache Memory error
1 long, 3 short	Conventional/Extended memory failure
1 long, 8 short	Display/Retrace test failed

Beep Code	Description
1 long, 2 short	Indicates a video error has occurred and the BIOS cannot initialize the video screen to display any additional information
Any other beep (s)	RAM problem

TONES	ERROR
Error Tone. (two sets of different tones)	Problem with logic board or SCSI bus
Startup tone, drive spins, no video	Problem with video controller
Powers on, no tone	Logic board problem
High Tone, four higher tones	Problem with SIMM

ERROR	DESCRIPTION
BIOS ROM checksum error - System halted	The checksum of the BIOS code in the BIOS chip is incorrect, indicating the BIOS code may have become corrupt. Contact your system dealer to replace the BIOS
CMOS battery failed	The CMOS battery is no longer functional. Contact your system dealer for a replacement battery
CMOS checksum error - Defaults loaded	Checksum of CMOS is incorrect, so the system loads the default equipment configuration. A checksum error may indicate that CMOS has become corrupt. This error may have been caused by a weak battery. Check the battery and replace if necessary
CPU at nnnn	Displays the running speed of the CPU
Display switch is set incorrectly	The display switch on the motherboard can be set to either monochrome or color. This message indicates the switch is set to a different setting than indicated in Setup. Determine which setting is correct, and then either turn off the system and change the jumper, or enter Setup and change the VIDEO selection
Press ESC to skip memory test	The user may press Esc to skip the full memory test
Floppy disk (s) fail	Cannot find or initialize the floppy drive controller or the drive. Make sure the controller is installed correctly. If no floppy drives are installed, be sure the Diskette Drive selection in Setup is set to NONE or AUTO
HARD DISK initializing Please wait a moment	Some hard drives require extra time to initialize
HARD DISK INSTALL FAILURE	Cannot find or initialize the hard drive controller or the drive. Make sure the controller is installed correctly. If no hard drives are installed, be sure the Hard Drive selection in Setup is set to NONE
Hard disk (s) diagnosis fail	The system may run specific disk diagnostic routines. This message appears if one or more hard disks return an error when the diagnostics run
Keyboard error or no keyboard present	Cannot initialize the keyboard. Make sure the keyboard is attached correctly and no keys are pressed during POST. To purposely configure the system without a keyboard, set the error halt condition in Setup to HALT ON ALL, BUT KEYBOARD. The BIOS then ignores the missing keyboard during POST
Keyboard is locked out - Unlock the key	This message usually indicates that one or more keys have been pressed during the keyboard tests. Be sure no objects are resting on the keyboard
Memory Test:	This message displays during a full memory test, counting down the memory areas being tested
Memory test fail	If POST detects an error during memory testing, additional information appears giving specifics about the type and location of the memory error
Override enabled - Defaults loaded	If the system cannot boot using the current CMOS configuration, the BIOS can override the current configuration with a set of BIOS defaults designed for the most stable, minimal-performance system operations
Press TAB to show POST screen	System OEMs may replace the Phoenix Technologies' Award BIOS POST display with their own proprietary display. Including this message in the OEM display permits the operator to switch between the OEM display and the default POST display
Primary master hard disk fail	POST detects an error in the primary master IDE hard drive
Primary slave hard disk fail	POST detects an error in the secondary master IDE hard drive
Resuming from disk, Press TAB to show POST screen	Phoenix Technologies offers a save-to-disk feature for notebook computers. This message may appear when the operator re-starts the system after a save-to-disk shut-down. See the Press Tab & message above for a description of this feature
Secondary master hard disk fail	POST detects an error in the primary slave IDE hard drive
Secondary slave hard disk fail	POST detects an error in the secondary slave IDE hard drive

Number of Beeps	Description
1	Memory refresh timer error
2	Parity error
3	Main memory read / write test error
4	Motherboard timer not operational
5	Processor error
6	Keyboard controller BAT test error
7	General exception error
8	Display memory error
9	ROM checksum error
10	CMOS shutdown register read / write error
11	Cache memory bad



Number of Beeps	Troubleshooting Action
1,2, or 3	Reseat the memory, or replace with known good modules.
4-7, or 9-11	Fatal error indicating a serious problem with the system. Consult your system manufacturer. Before declaring your motherboard beyond all hope, eliminate the possibility of interference by a malfunctioning add-in card. Remove all expansion cards except the video adapter. If the beep codes are generated even when all other expansion cards are absent, the motherboard has a serious problem. Consult your system manufacturer. If the beep codes are not generated when all other expansion cards are absent, one of the add-in cards is causing the malfunction. Insert the cards back into the system one at a time until the problem happens again. This will reveal the mal-functioning add-in card.
8	If the system video adapter is an add-in card, replace or reseat the video adapter. If the video adapter is an integrated part of the system board, the board may be faulty.