Computer POST and beep codes

The computer power-on self-test (POST) tests the computer to make sure it meets the necessary system requirements and that all hardware is working properly before starting the remainder of the boot process. If the computer passes the POST, the computer gives a single beep (with some computer BIOS manufacturers it may beep twice) as it starts up and will continue to start normally. However, if the computer fails the POST, the computer will either not beep at all or will generate a beep code, which tells the user the source of the problem.

If you're receiving an irregular POST or a beep code not mentioned below, follow the POST troubleshooting steps to determine the failing hardware component.

AMI BIOS beep codes
Award BIOS beep codes
Dell beep codes
IBM BIOS beep codes
Macintosh startup tones
Phoenix BIOS beep codes
Motherboard help

AMI BIOS beep codes

Below are the AMI BIOS Beep codes that can occur. However, because of the wide variety of different computer manufacturers with this BIOS, the beep codes may vary.

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
two-tone siren	Low CPU Fan speed, Voltage Level issue

AWARD BIOS beep codes

Below are Award BIOS Beep codes that can occur. However, because of the wide variety of different computer manufacturers with this BIOS, the beep codes may vary.

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.

If any other correctable hardware issues are found, the BIOS displays a message.

Dell beep codes

Beep Code	Description
7 beeps (repeated)	Bad processor (CPU)

For other Dell beep codes, please refer to Dell's Beep Codes and PSA Diagnostics Chart page.

IBM BIOS beep codes

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

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 or Keyboard card error.
One Beep, Blank or Incorrect Display	Video Display Circuitry.

Macintosh startup tones

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.

Phoenix BIOS beep codes

Below are the beep codes for Phoenix BIOS Q3.07 OR 4.X

Beep Code	Description and what to check
1-1-1-1	Unconfirmed beep code. Reseat RAM chips or replace RAM chips as possible solution
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.
two-tone siren	Low CPU Fan speed, Voltage Level issue

How to enter the BIOS or CMOS setup

Because of the wide variety of computer and BIOS manufacturers over the evolution of computers, there are numerous ways to enter the BIOS or CMOS Setup. Below is a listing of most of these methods, as well as other recommendations for entering the BIOS setup.

Note: This document does not help if you cannot enter the BIOS or CMOS setup because of a password.

New computers

Computers manufactured in the last few years allow you to enter the BIOS setup using one of the five keys shown below during the boot process. Typically it is one of the first three keys.

• F1
• F2
• DEL
• ESC
• F10 *

* F10 is also used for the boot menu. If F10 opens a boot menu, your setup key is likely F2.

You will know when to press this key when you see a message similar to the example below as the computer is booting. Some older computers may also display a flashing block to indicate when to press the F1 or F2 keys.

Press <F2> to enter BIOS setup

Tip: If your computer is a new computer and you are unsure of what key to press when the computer is booting, try pressing and holding one or more keys on the keyboard to cause a stuck key error. Once you get this error, you should have the option to continue or enter setup.

Once you have successfully entered the CMOS setup, you should see a screen similar to the example below.

How do I change and save changes in CMOS setup?

Once in CMOS setup, the method for changing the settings often depends on the BIOS manufacturer. Typically you can change the settings by using the arrow keys to move to the option you want to change. Press Enter to select what to change and then use the arrow keys to select a new value. Some manufacturers may have you press the Page up and Page down keys to change the values.

Tip: All manufacturers list the steps on how to navigate on the bottom or right-hand side of the screen.

I cannot change the values to a setting I want to use.

If you are trying to change the clock settings, speed settings, or other setting and do not have an available option, it is because it is not supported by the motherboard. If you believe it should be supported, you may need a BIOS update.

Older computers

Unlike the computers of today, older computers (before 1995) had numerous different methods of entering the BIOS setup. Below is a listing of key sequences to press as the computer is booting to enter setup.

• CTRL + ALT + ESC
• CTRL + ALT + INS
• CTRL + ALT + ENTER
• CTRL + ALT + S
• PAGE UP KEY
• PAGE DOWN KEY

ACER BIOS

If your computer cannot boot or you want to restore the BIOS back to its bootable settings and your computer uses an ACER BIOS, press and hold the F10 key as you turn on the computer. While continuing to hold the F10 key, you should hear two beeps indicating that the settings are restored.

AMI BIOS

Older AMI BIOS could be restored back to bootable settings by pressing and holding the Insert key as the computer is booting.

BIOS or CMOS diskettes

Early 486, 386, and 286 computers required a floppy disk in order to enter the BIOS setup. These diskettes may be referred to as ICU, BBU, or SCU disks. Because these diskettes are unique to your computer manufacturer, you must obtain the diskettes from them. See the computer manufacturers list for contact information.

Early IBM computers

Some early IBM computers require you to press and hold both mouse buttons as the computer boots to enter the BIOS setup.

Other suggestions

Finally, if none of the above suggestions help get you into your CMOS setup, you can cause a stuck key error, which causes the CMOS setup prompt to appear and remain until you press a key to continue. To do this, press and hold any key on the keyboard and do not let go (you may get several beeps as you are doing this). Keep pressing the key until the computer stops booting and you have the option to enter setup.

CMOS

Alternatively referred to as a Real-Time Clock (RTC), Non-Volatile RAM (NVRAM) or CMOS RAM, CMOS is short for Complementary Metal-Oxide Semiconductor. CMOS is an on-board semiconductor chip powered by a CMOS battery inside computers that stores information such as the system time and date and the system hardware settings for your computer. The picture shows an example of the most common CMOS coin cell battery used in a computer to power the CMOS memory.

A Motorola 146818 chip was the first RTC and CMOS RAM chip to be used in early IBM computers. The chip was capable of storing a total of 64 bytes of data. Since the system clock used 14 bytes of RAM, this left an additional 50 bytes of space that was available for IBM to store system settings. Today, most computers have moved the settings from a separate chip and incorporated them into the southbridge or Super I/O chips.

How long does the CMOS battery last?

The standard lifetime of a CMOS battery is around 10 Years. However, this can vary depending on the use and environment that the computer resides. When the battery fails the system settings and the date and time will not be saved when the computer is turned off until the battery has been replaced.

Boot menu

When a computer is starting up, a user can access the boot menu by pressing one of several keyboard keys, including Esc, F10 or F12, depending on the manufacturer of the computer or motherboard. The specific key to press is usually specified on the computer's startup screen. The boot menu allows a user to select what device to load an operating system or application from as the computer is booting. The boot menu can contain a number of different device options to boot to, including CD or DVD drives, hard drives, USB flash drives and a LAN (network). This allows a user to load up other operating systems or applications, even if the computer itself already has an operating system on it. This is also useful when trying to install a new operating system on a computer, and the user needs to load the installation application from a CD or DVD.

How to replace the CMOS battery

If your computer is losing its time or date settings, or you are receiving a message CMOS Read Error, CMOS checksum error, or CMOS Battery Failure, first try leaving the computer on for 24-hours. In some cases, this can charge the battery and resolve your problem. This fixes most CMOS battery issues on computers left without power for several months. If this does not resolve your problem follow the steps below.

Locate your CMOS battery

Caution: When inside your computer make sure you are aware of ESD and its dangers.

Open the computer case and find the battery on the computer motherboard, verify that it is accessible and can be removed. Today, most computers use a coin cell CMOS battery as shown in the picture.

Tip: Some CMOS batteries may be held down by a metal clip or bar. This clip just holds the battery in place and the battery can still be removed by sliding it under the clip. Do not bend this clip to get the battery out.

If you are unable to locate your CMOS battery refer to your motherboard or computer documentation or contact your computer manufacturer for additional assistance in locating it.

Note: With some computers you may need to disconnect cables, remove drives, or remove other parts of the computer to get full access to the CMOS battery.

Obtain battery information

Unfortunately, most manufacturers do not list the exact type and model of your CMOS battery; therefore, once you have located the battery, write down all information about the battery (Voltage, chemistry, wiring, and packaging). If possible, remove the battery and take it to the retail location.

Tip: The part number for this battery for most computers is CR2032.

• Additional buying information is on our battery buying tips page.

Removing the battery

Caution: When inside your computer make sure you are aware of ESD and all its potential dangers.

If your computer is using a coin cell battery removing the battery is relatively simple. Use your fingers to grab on the edge of the battery and pull it up and out of the container holding it. Some motherboards have a clip holding the battery down. If your computer has this clip you may need to use one hand to move the clip up and the other hand to pull the battery out.

Unfortunately, not all CMOS batteries are removable; some manufacturers only allow a replacement battery to be added. If your computer does not have a coin cell battery and you are not sure how to remove the battery refer to your motherboard or computer documentation or contact your computer manufacturer for additional assistance in removing the battery or how to insert a new replacement battery.

Users with computers that do not have removable batteries only options to install a new battery will most likely also need to set a jumper when adding the new battery into their computer.

Insert the new battery

After purchasing a new battery, remove the old battery and replace it with a new battery.

Enter CMOS values

Once the battery is replaced turn on the computer and resetting the CMOS values to the defaults. After the values have all been entered make sure to save the settings before exiting. Many CMOS setups allow you to press a key (such as F10) to save values and exit all in one action.

Bad hardware

If after following all the above steps you continue to experience the same error when your computer starts or your computer is still unable to keep the stored values you are experiencing a more serious issues. Most likely causes are bad power supply or bad motherboard.

Motherboard

Alternatively referred to as the mb, mainboard, mobo, mobd, backplane board, base board, main circuit board, planar board, system board, or a logic board on Apple computers. The motherboard is a printed circuit board that is the foundation of a computer, located at the bottom of the computer case. It allocates power to the CPU, RAM, and all other computer hardware components and allows them to communicate with one another.

Below is a graphic illustration of the ASUS P5AD2-E motherboard and some basic explanations of each of the major portions of the motherboard. Clicking on the image below gives you a larger more detailed version of the picture below.

Motherboard components

Below is a listing of links that describe each of the above mentioned motherboard components in additional detail. Links are listed in clockwise order going from the top-left corner of the image. Components not listed above or found on other motherboards are listed in the next section.

• Expansion slots (PCI Express, PCI, and AGP)
• 3-pin case fan connectors
• Back pane connectors
• Heatsink
• 4-Pin (P4) power connector
• Inductor
• Capacitor
• CPU Socket
• Northbridge
• Screw hole
• Memory slot
• Super I/O
• Floppy connection
• ATA (IDE) disk drive primary connection
• 24-pin ATX power Supply connector
• Serial ATA connections
• Coin cell battery (CMOS backup battery)
• RAID
• System panel connectors
• FWH
• Southbridge
• Serial port connector
• USB headers
• Jumpers
• Integrated circuit
• 1394 headers
• SPDIF
• CD-IN

Other motherboard components

Below is a listing of other motherboard components that are not shown in the above picture or have been part of older computer motherboards.

• BIOS
• Bus
• Cache memory
• Chipset
• Diode
• Dip switches
• Electrolytic
• Fuse
• Game port and MIDI header
• Internal speaker
• Keyboard controller
• LCC
• Network header
• Obsolete expansion slots (AMR, CNR, EISA, ISA, VESA)
• Obsolete memory slots (SIMM)
• Onboard LED
• Parallel port header
• PS/2 header
• Resistor
• RTC
• Serial port header
• Screw hole aka mounting hole
• SCSI
• Solenoid
• Voltage regulator
• Voltage regulator module (VRM)

Motherboard form factors

As computers advanced, so have motherboards. Below is a listing of the various motherboard form factors and additional information about each of these form factors including ATX the most commonly used motherboard form factor today.

• AT
• ATX
• Baby AT
• BTX
• DTX
• LPX
• Full AT
• Full ATX
• microATX
• NLX

Since there is a motherboard, is there a fatherboard?

No, there is no such thing as a fatherboard when talking about a computer. However, there is such a thing as a daughterboard.

What are the F1 through F12 keys?

Commonly known as function keys, F1 through F12 may have a variety of different uses or no use at all. The operating system installed on the computer and the software program currently open can change how each of these keys operate. A program is capable of not only using each of the function keys, but also combining the function keys with the ALT or CTRL key. For example, Microsoft Windows users can press ALT + F4 to close the program currently active.

Note: Some keyboards include additional functions on the function keys, which can be activated by pressing the FN key, usually located near the CTRL key, and the appropriate function key. The additional functions available with the use of the FN key will differ depending on the type and brand of keyboard being used.

If your keyboard does not have a row of function keys, they are probably set up as secondary functions on other keys. Some laptop keyboards are set up this way to save space. They can be activated by pressing another key plus the key with the secondary F key functionality.
Below is a short-listing of some of the common functions of the functions keys. As mentioned above not all programs support function keys and may perform different tasks then those mentioned below. If you are looking for more specific shortcut keys and function key examples, we suggest seeing our shortcut key page.

F1

• Almost always used as the help key, almost every program opens a help screen when this key is pressed.
• Enter CMOS Setup.
• Windows Key + F1 would open the Microsoft Windows help and support center.
• Open the Task Pane.

F2

• In Windows renames a highlighted icon, file, or folder in all versions of Windows.
• Alt + Ctrl + F2 opens document window in Microsoft Word.
• Ctrl + F2 displays the print preview window in Microsoft Word.
• Quickly rename a selected file or folder.
• Enter CMOS Setup.

F3

• Often opens a search feature for many programs including Microsoft Windows when at the Windows Desktop..
• In MS-DOS or Windows command line F3 will repeat the last command.
• Shift + F3 will change the text in Microsoft Word from upper to lower case or a capital letter at the beginning of every word.
• Windows Key + F3 opens the Advanced find window in Microsoft Outlook.
• Open Mission Control on an Apple computer running Mac OS X.

F4

• Open find window in Windows 95 to XP.
• Open the address bar in Windows Explorer and Internet Explorer.
• Repeat the last action performed (Word 2000+)
• Alt + F4 closes the program window currently active in Microsoft Windows.
• Ctrl + F4 closes the open window within the current active window in Microsoft Windows.

F5

• In all modern Internet browsers, pressing F5 will refresh or reload the page or document window.
• Open the find, replace, and go to window in Microsoft Word.
• Starts a slideshow in PowerPoint.

F6

• Move the cursor to the Address bar in Internet Explorer, Mozilla Firefox, and most other Internet browsers.
• Ctrl + Shift + F6 opens to another open Microsoft Word document.

F7

• Commonly used to spell check and grammar check a document in Microsoft programs such as Microsoft Word, Outlook, etc.
• Shift + F7 runs a Thesaurus check on the word highlighted.
• Turns on Caret browsing in Mozilla Firefox.

F8

• Function key used to enter the Windows startup menu, commonly used to access Windows Safe Mode.
• Used by some computers to access the Windows Recovery system, but may require a Windows installation CD
• Displays a thumbnail image for all workspaces in Mac OS

F9

• Refresh document in Microsoft Word.
• Send and receive e-mail in Microsoft Outlook.
• Opens the Measurements toolbar in Quark 5.0.
• With Mac OS 10.3 or later, displays a thumbnail for each window in a single workspace.
• Using the Fn key and F9 at the same time opens Mission Control on an Apple computer running Mac OS X.

F10

• In Microsoft Windows activates the menu bar of an open application.
• Shift + F10 is the same as right-clicking on a highlighted icon, file, or Internet link.
• Access the hidden recovery partition on HP and Sony computers.
• Enter CMOS Setup.
• With Mac OS 10.3 or later, shows all open Windows for the active program.

F11

• Enter and exit full screen mode in all modern Internet browsers.
• Ctrl + F11 as computer is starting to access the hidden recovery partition on many Dell computers.
• Access the hidden recovery partition on eMachines, Gateway, and Lenovo computers.
• With Mac OS 10.4 or later, hides all open windows and shows the Desktop.

F12

• Open the Save as window in Microsoft Word.
• Ctrl + F12 opens a document In Word.
• Shift + F12 saves the Microsoft Word document (like Ctrl + S).
• Ctrl + Shift + F12 prints a document in Microsoft Word.
• Preview a page in Microsoft Expression Web.
• Open Firebug or browser debug tool.
• With an Apple running Mac OS 10.4 or later, F12 shows or hides the Dashboard.
• Access the list of bootable devices on a computer at startup, allowing you to select a different device to boot from (Hard drive, CD or DVD drive, Floppy drive, USB drive, Network)

F13 - F24

Early IBM computers also had keyboards with F13 through F24 keys. However, because these keyboards are no longer used, they are not listed on this page.