Power on, POST, and Boot

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Power on, POST, and Boot: Which is which?


 digraph D {
  node [fontname="Helvetica", fontsize="11"]
  edge [fontname="Helvetica"]
  poweron        [label="POWER ON", shape="box", style="bold"]
  post           [label="POST", shape="box", style="bold"]
  boot           [label="BOOT", shape="box", style="bold"]
  poweron -> post -> boot

</graphvizl> In Getting the Processor Information you are asked a few times if the system POSTs or not. In order to answer this question, you need to know the difference between power on, POST, and boot -- the three things a computer does on startup.

Power on
is what happens when the systems first gets electricity. You may hear a beep or a fan or see the lights come on.
means Power On Self Test and is a basic system check that happens once the system has powered on successfully.
means the computer is loading an operating system, typically off of the hard drive (but it also could load the OS off of a floppy, a CD, or even over the network).

If you see a system trying to boot, then you know it must have POSTed. This means that if you see an OS load (i.e. a system boots to Windows or Linux) then the POST was successful. Likewise, if you see a message similar to "Operating System not found" then the boot is failing, but of course this also mean that the system successfully POSTed.

NOTE: We never want to boot from an OS. We, however, do want to try to get the system to POST.

NOTE: A system does not need to POST. We just want to try. If a system fails to POST, that is not necessarily a reason to recycle it.

Accessing BIOS during POST

When a system POSTs it may tell you the processor class and speed, as well as other useful information. You need to keep a sharp eye out for information and clues since it can scroll by very fast. In some cases, the information is completely hidden and you will need to access BIOS to either see the information you are looking for, or to change the configuration, so the POST is more useful.

You are usually able to get into BIOS (or SETUP) during POST, even if you don't see anything useful on the monitor. While POST is happening, hit the appropriate key to enter BIOS. Which key? That depends. Sometimes the key is listed on the screen. (Pay attention as POST proceeds.) Other times you'll need to experiment. Try all the F-keys, DELETE, INSERT, and TAB, or just drag your hand across the whole keyboard.

This might take a few times to hit the right key at the right time. Try it a few times. Don't be shy.

Once in BIOS, you may see what you're looking for, or you might need to change some settings. Look for an option called Quiet Boot or something similar and disable it. (Or perhaps Diagnostic Boot or BIOS Boot -- eanble that.) Also look for Quick Boot and disable it to give you time to read what's on the screen.

When finished, be sure to save your changes and reboot. Then you may get the information you are looking for.