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All You Need To Know About POST Errors: Power On Self-Test

What is POST?

At the first instance you must be thinking of it as an article or message that’s been posted online. But frankly speaking this POST is somehow different and has nothing to do with Internet.

POST, an abbreviation for Power on Self-Test. It is actually the foremost step performed by a firmware or software when your computer or any other electronic appliances are turned on.

POST is not related to computers only, rather it is related with some other daily needs appliances also. The appliances may include avionics, communications, or medical equipment.


How Start up Process is related to POST?

A POST is one of the basic elements needed for the proper functioning of a computer system like that of   peripheral devices and hardware elements which include processor, storage devices, and memory.

Your computer systems can only starts to Boot up after the POST is successful. In order for a computer to successfully boot, its BIOS, operating system and hardware components must all be working properly; failure of any one of these three elements will likely result in a failed boot sequence.

POST doesn’t rely on any specific operating system. In fact, there doesn’t even need to be an OS installed on a hard drive for the POST to run. This is because the test is handled by the system’s BIOS, not any installed software.


Working Mechanism of POST

POST runs on both Windows and Mac, while the tests may vary depending on the system. But the main focus is basically on the Memory Error. The other possible errors which it focuses are power supply, RAM, and system bus.

In Mac OS computers, POST errors often appear as an icon or some other graphic instead of an actual error message.

For example, a broken folder icon after starting up your Mac may mean that the computer can’t find a suitable hard drive to boot from.

Whereas in Windows, as soon as you turn ON the power button of your computer. You will be triggered by a series of clock ticks generated by the system clock. The ROM BIOS stores the first instruction. This is the instruction to run the power-on self-test (POST), in a predetermined memory address. POST begins by checking the BIOS chip and then tests CMOS RAM.

If the POST does not detect a battery failure, it then continues to initialize the CPU. Checking the inventoried hardware devices (such as the video card), secondary storage devices, such as hard drives and floppy drives, ports. And other hardware devices, such as the keyboard and mouse, to ensure they are functioning properly.



Problems faced During the POST

POST is an error code that usually restricts user to carry out its work unless and until they fix that error. Their are many problems that come in its path, chief among them are flashing LEDs, audible beeps, or error messages on the monitor. All of which are technically referred to as POST codes, beep codes, and on-screen POST error messages, respectively.

Certain types of failures during the POST may not produce an error at all, or the error may hide behind a computer manufacturer’s logo.

For example, if the problem lies with the video card, and therefore you can’t see anything on the monitor. Then looking for an error message wouldn’t be as helpful as listening for a beep code or reading a POST code with a POST test card.

Since the issues caused by POSTS are varied so, it is better to follow the troubleshooting mechanism to minimize the problems caused by it.


# POST code

A POST code is referred to as a 2 digit hexadecimal code generated during the Power On Self-Test. If

post-codesometimes you get encountered with this error code, you must be thinking of it as a system error code or any relevant errors. However it is different from System error code, STOP code, a device manager error code, or an HTTP status code. POST codes correspond directly to tests that are taking place by the POST.

It is also known as Power on Self-Test Code or test-point error code. The POST codes are different for the different system as it depends upon the BIOS Vendor, means most motherboards uses their own lists.

# Beep Code


beep-codeA signal given out by computer in form of audio is known as beep code. It actually announces the result of a short diagnostic testing sequence that the computer performs during first powering up of the system. The beeping sequence is actually a coded message (beep code) which tells user what is wrong with the computer.

When the computer is turned on, POST starts its activity. If everything tests out correctly, the computer will typically emit a single beep and continue the starting-up process. If something is wrong, the computer will display an error message on the monitor screen and announce the errors audibly with a series of beeps that vary in pitch, number and duration.


# POST Error Message

POST Error Message is yet another type of error messages that you witness while accessing your electronic appliances. In this error message if the BIOS encounters any issues, an error message will post-error-messageprompt on your screen. A POST error message is sometimes called as BIOS error message, POST message, or POST screen message.

Your computer usually displays a POST code or a Beep code but sometimes may greet you with the POST error message as well.  It will only display on screen if the computer is capable of booting this far. POST error messages are usually fairly descriptive and should give you enough information to begin troubleshooting whatever problem the POST found.


# Step-wise Troubleshooting POST Issues



How to Fix Stopping, Freezing, and Reboot Issues During the POST


Whenever you start up your system it may either starts to work or may prompt an error message on your screen which eventually stops your Boot process.

Sometimes you can notice that your PC freezes up without any error message and you’ll see your computer maker’s logo on the screen.

In order to minimize the risk of Stopping, Freezing and Reboot issues, it is better to follow the steps that have been created to help the user.

Step 1.

Firstly, identify the cause and then troubleshoot the cause of the BIOS error message you see on the monitor. These errors are usually specific. So, if you have come across any then don’t get panic and choose best course of action to troubleshoot to the specific error you see.

Step 2.

If any USB is connected with the system then better to disconnect and remove any discs in any optical drives. If your computer is trying to boot from a location that doesn’t actually have bootable data on it. Then your computer could freeze somewhere during the POST.

If this step works then change the boot order. You can do this by adding the preferred boot device i.e. the internal hard drive of the system before USB.

Step 3.

Clear the CMOS (complementary metal-oxide-semiconductor). Clearing the BIOS memory on your motherboard will reset the BIOS settings to their factory default levels. As a Misconfigured BIOS is a common cause of a computer locking up during the POST.

If it works then it’s better to make any future settings changes in BIOS one at a time so if the problem returns, you’ll know which change caused your issue. And next time you will be able to fix the issue easily.

Step 4.

Test the Power supply of your computer. When you switch on the power button, it does not mean that the power supply is working. Till now power supply is the major cause of startup problems more than any other piece of hardware in computer.

Do not skip a test of your PSU thinking that your problem can’t be with the power supply because your computer is receiving power. Power supplies can, and often do; partially work and one that isn’t fully functional must be replaced.

Step 5.

Reseat everything inside your computer case. This will rearrange the cable, card, and other connections inside your computer. And you will clearly be able figure out the problem if caused by these units.

You can also go to unplug and reattach your keyboard and mouse as well. Although there is little chance that the keyboard or mouse is causing your computer to freeze during the POST but just do it.

Step 6.

If you think that your CPU may have become loose or might not have been properly installed, you can reseat your CPU as well.

Step 7.

Just go for a triple check every hardware configuration. Check every jumper and DIP switch, verify that the CPU, memory, and video card you’re using is compatible with your motherboard, etc. A complete focus on the each and every element might provide you a reason. Rebuild your PC from scratch if necessary.

Step 8.

One can also go for checking the cause of electrical shorts inside the computer. This can be the cause of the problem if your computer freezes during the POST, especially if it does so without a BIOS error message.

Step 9.

Start your PC with essential hardware only. The purpose here is to remove as much hardware as possible while still maintaining your computer’s ability to power on.

Step 10.

Reinstall each piece of hardware that you removed in Step 8, one piece at a time, testing your PC after each installation. Checking out the entire process and if output comes then go to change the settings as well.

Step 11.

Test your computer’s hardware using a Power On Self-Test card. If your computer is still freezing during the POST with nothing but essential computer hardware installed. POST card will help identify which piece of remaining hardware is causing your computer to stop booting.

Step 12.

Replace each piece of essential hardware in your PC with an identical or equivalent spare piece of hardware (that you know is working). One component at a time, to determine which piece is causing your computer to stop during the POST. Test after each hardware replacement to determine which component is faulty.

Step 13.

Finally, if all else fails, you’ll probably need to find professional help from a computer repair service or from your computer manufacturer’s technical support.

If you don’t have a POST card or spare parts to swap in and out. You’re left not knowing which piece of your essential computer hardware is not working. In these cases, you’ll have to rely on the help of individuals or companies that do have these tools and resources.


As per my information, I have covered all the information related to POST. If you have any queries or wanted to know more about this very topic, then feel free to ask us.

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