The simple answer here is that the computer will NOT POST without a CPU as far as DISPLAYING the POST screen is concerned, however, it may flash LEDs or make beeping sounds which is also considered a function of the POST.
The motherboard on your computer is a very important component. It is literally the nervous system of the computer since it interconnects all the components that need to communicate with the CPU, allowing the transfer of information and instructions between them.
In order for it to be the literal network highway of your PC, it has to test if all the components connected are functional. This include the CPU, RAM, Graphics Processing Unit and even peripherals such as a Keyboard. That is the purpose of POST.
Here we will look further into what POST is and also attempt to clarity the answer to the question: “Will motherboard post without CPU?”
What is POST?
The term is an acronym for Power-On-Self-Test.
The main purpose of this test is to find out whether the computer’s components are working as expected. This include the core components such as the CPU, GPU, RAM as well as storage, and connectivity peripherals such as keyboard.
It is the most initial test the computer runs for checking various critical systems. Only when the POST is successful can the computer continue the boot up processor. If it fails, the POST screen will either display where the malfunction is occurring (like no keyboard detected) or generate a beeping sound code.
Computer runs this operation in the most initial stage to avoid any inconveniences to the user later on, like a malfunctioning keyboard or other errors with disk drives and other components.
So basically, the POST is used to detect hardware problems with the computer before it finishes booting up.
Also Read: How to Test Motherboard Without CPU?
So Will Motherboard POST Without CPU?
If you are talking specifically about a typical PC, the simple answer is NO. A motherboard will NOT POST without a CPU.
As mentioned earlier, POST is the most initial test a PC performs to check the status of the hardware.
Therefore, the motherboard would not even attempt to display the POST screen without a CPU. This is because without a CPU, your video output ports wouldn’t even work to display the POST screen!
No CPU = No GPU = No Display = No POST Screen
Other than the fact that motherboard is literally missing its brains (CPU), the CPUs contains the primary controller for display.
In other words, the display ports i.e HDMI or VGA located on the motherboard are controlled by the CPU and NOT by the motherboard since CPUs have the integrated graphics. Motherboards DO NOT have onboard graphics processing unit.
Therefore, your display would show nothing, let along the POST screen.
Beeping Sound & Flashing LED
While no POST screen will be displayed on your screen without a CPU as mentioned earlier, your motherboard may flash LEDs or make beeping sounds indicating that something is amiss, which in this case would be the PC brain itself.
The only thing turning on a motherboard without a CPU would tell you is if its is dead or not, it would tell you nothing about whether its connected components, slots and ports are working properly or not.
Motherboard Beep Codes LED Flashes are Part of POST Process
While your motherboard may not display the POST screen without a CPU, it will create beep codes or LED flashes indicating where the issue lies. This is also part of the POST process.
Many motherboards come with a built in beep code speaker – if yours doesn’t, you can invest in a very cheap beep code speaker that you can install.
If the POST identifies any issues with the hardware, it will generate a beep sound code. The number of beeps it makes indicates where the trouble lies. So for instance
- 1 Beep – issues with the memory
- 2 Beeps – issues with the motherboard
- 5 Beeps – issues with the CPU
So on and so forth. If you do not have a CPU installed on the motherboard, you may hear a 5 beep sound code. PCMag.com has a complete list of all the beep codes and what they indicate.
Also Read: How to Connect Motherboard Internal Speaker? (Beep Code Speaker)
In addition to the beep code sound, your motherboard may also flash LEDs built on it.
The sequence of the LEDs flashing may indicate where the issues lies. For this, you will have to consult the manual of the motherboard.
Also Read: Which PCIe Slot for GPU is Ideal?
Should You Turn on Motherboard Without a CPU?
You CAN turn on the motherboard without a CPU. It shouldn’t cause any issues. In fact, this action can sometimes be important particularly if you want to test whether your motherboard is working or not.
What Happens When You Boot without a CPU?
Well, nothing much really. Other than the error codes and beeping sounds, the only thing you will observe is whether your motherboard is dead or alive.
You may also notice the case cooling fans start. But other than that, there is nothing more that you can expect to happen without a CPU on a motherboard.
Special Cases and Exceptions
For some motherboards, it is possible to update or FLASH BIOS without a CPU.
This is the case with some of the motherboards from ASUS and other manufacturers.
While you still won’t be able to access the BIOS even on these motherboard, you will be able to update the BIOS firmware without a CPU on them.
Some large scale mainframe computers such as those by IBMs and other enterprise level computer can POST and allow access to BIOS without a dedicated CPU installed.
But of course to you as an average user, this matters not.
Also Read: LGA vs PGA CPUs
Power-On-Self-Test or POST is used to ensure that your computer is properly configured and has all the critical components working fine.
After POST is completed, the computer resumes its booting process, initializing the various systems and programs it needs to work.
Therefore, when the POST process does not detect the CPU, then for starters nothing will be displayed on your monitor. And then subsequently, your motherboard will generate error codes in the form of beeping sound and LED Flashes.
So the answer to the question “will motherboard POST without CPU?”, in the traditional sense is NO. Meaning you will not see the POST screen on your monitor.
However, since beeping sound codes and LED Flashes are also part of the POST process, you could say the motherboard will initiate the POST process but will not succeed in completing it.