Building your own PC is a little like rock climbing but without a harness. Okay, it’s not quite as dangerous, but unlike picking up an off-the-shelf computer, you are your own support staff – unguided by “tech experts” of big corporations – if something goes wrong. One could try to get support from individual component makers, but most of the time, the hardware issues are relatively complicated and involve multiple components. It is here that some basic knowledge about PC diagnostics comes to your aid. And one of the most effective of them, at least in case of hardware failure, is the ability to read Motherboard POST codes. These codes are remarkable tools that come to life during the start-up process. And if you read them right, they can help you save your dying computer. So what are BIOS POST codes? And how can they help you fix your PC? Let’s find out.
In this article, we will explore the diagnostic method called BIOS POST codes. We will discuss everything about post codes, ranging from what they are and how we can view them to giving you a detailed rundown of what each post code means. We will also compare POST codes and motherboard beep codes as they are sometimes seen as synonymous to each other. We will explore how this accident of abstraction is a mistake, as both of them differ in both complexity and method.
What is POST in Computers?What Are BIOS Post Codes? How Do They Differ from Beep Codes?How to Find out Which BIOS Manufacturer You Have?List of BIOS POST Codes for Motherboard Manufacturers
AMI Motherboard BIOS POST CodesPhoenix Motherboard PCI POST CodesASUS Motherboard Q-Code (POST)ASRock Motherboard Dr. Debug POST CodesPOST Code Alternative: On-screen Error MessagesMotherboard BIOS POST Codes Explained
AMI Motherboard BIOS POST CodesPhoenix Motherboard PCI POST CodesASUS Motherboard Q-Code (POST)ASRock Motherboard Dr. Debug POST Codes
What is POST in Computers?
When you press your computer’s power button, multiple actions take place in the background, even before you see anything on your screen. These actions are collectively called the power-on self-test (POST). How does POST work, though? Essentially, each time the user turns on their PC, the UEFI/ BIOS gathers information about the major system components and performs a special test called the Power On Self Test to make sure that each component is functioning properly.
While the entire process is more complicated than that and involves intricacies related to memory and system partitioning, the thing you need to keep in mind is that it’s a kind of a diagnostic test. So if any particular part of the test fails, the BIOS figures out where the failure took place and displays an error message on the monitor, or if it occurs before the video signal, then on the POST code display.
You might already be familiar with Motherboard BIOS beep codes. Essentially, beep codes use audible signals, which alert users when they are facing a particular problem during start-up. They can range from a single short beep, which signals everything is OK, to multiple beeps in different tones to convey a more complex message. These beep codes are especially useful when a hardware failure occurs before the video card is initialized.
While some sets of beep codes, such as the ones generated by the latest Phoenix BIOS, can provide extensive troubleshooting information, most BIOS manufacturers tend to keep their list of beep codes rather simple. For example, popular computer brands like Dell and Lenovo only include 10 or so beep codes in their BIOS memory. That means most BIOS beep codes aren’t able to provide extensive troubleshooting information.
Most of the time, a diagnostic board called the POST card is used to read these codes. It’s plugged into a computer’s peripheral bus, where it reads the last POST code displayed before the system locked up and identifies the problem area. Not too long ago, most of the POST cards were based on the ISA bus, but the latest models are now being made to fit into PCI slots because ISA has largely become obsolete.
Furthermore, for diagnosing portable systems and avoiding the need to open a system to insert a POST card, some brands such as Ultra-X offer a Micro POST display unit that attaches to common ports like USB or Parallel. These cards have emerged as a viable alternative to regular POST cards as they are easier to use and do not require a deep understanding of motherboards. You simply need to plug them into your USB slot, and voila, they show you the BIOS POST code!
How to Find out Which BIOS Manufacturer You Have?
Just like Beep codes, the POST codes can vary a lot from BIOS to BIOS, as there is no standardization in this aspect. And unlike beep codes, you also don’t have general thumb rules like “one quick beep means that everything is working fine”.
But as we saw with beep codes, modern day motherboard manuals like that of the ASUS Z690 Gaming board (image attached above) do not explicitly mention POST codes on their manual. The reason could be similar to the ones faced by beep codes, i.e. POST displays are increasingly becoming rarer as the industry has moved towards newer diagnosing practices like LED light indicators.
In case you don’t have your motherboard manual, we have discussed the different ways to find which BIOS manufacturer you have in our dedicated article on motherboard beep codes. But, to briefly recap the options, you can figure out your motherboard’s BIOS manufacturer using the system information panel in Windows 10/11, using a third-party application like CPU-Z (Free), or simply by going old-school and opening your PC case to find your BIOS chip.
This makes interpreting POST codes even more tricky than the already obscure beep codes. For example, if you look at the list of POST codes for AMI motherboards on BIOS central, you would see that each particular BIOS iteration, be it 1.0 or 2.2, has hundreds of different combinations of POST codes that detail each and every issue that can arise during the boot up process.
Phoenix Motherboard PCI POST Codes
ASUS Motherboard Q-Code (POST)
Things do become simpler when we get to popular gaming manufacturers like ASUS and ASRock, as these motherboards tend to attract buyers who are into overclocking. Why, you may ask? Simply because overclockers tend to push their PC a lot in terms of voltage, clock speeds, and memory performance, which causes the PC to frequently shut down. This creates a situation where overclockers continuously have to troubleshoot their system, and if POST codes help them in this regard, it’s highly valuable.
POST codeWhat It Means8CPU not detected4B/FA No DRAM detected/installedF9/0DDRAM training failed90/CFDRAM recovery06DRAM unstable A0-A2Boot up device unstableB2External device unstableD6Graphics card unstableAABoot into the system
POST Code Alternative: On-screen Error Messages
While beep codes and POST codes are some of the better ways to diagnose a problematic PC, there are other troubleshooting methods that are much easier than them to make sense of. The easiest of all error methods is the on-screen error message that appears right before the POST is completed.
Furthermore, because the video circuits are tested after components such as the motherboard, CPU, and BIOS, an on-screen error message is usually indicative of a less-serious error than one that is reported with beep codes. More serious errors like CPU or memory failure will still be reliant on POST codes or beep codes.
