Does the POST execute from RAM or just from the flash ROM in computers?

By rodion15
Aug 30, 2015
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  1. I'd welcome if somebody directed to some article, video or whatever explaining the startup process in depth.
    For example, I've never known if the POST and boot loader is passed from the flash rom chip to RAM and executed the from RAM or it's executed from the flash rom directly.
    I also don't understand why a CMOS with battery is needed, couldn't the cmos settings be stored on a chunk of flash rom just like that used in usb flash drives.
    I'd welcome good articles explaining this.

    Many thanks [​IMG]
  2. cliffordcooley

    cliffordcooley TS Guardian Fighter Posts: 9,726   +3,700

    It is the system clock that mainly needs a battery. As for storing settings, you have to remember how long the current system has been working. And the fact that as long as a battery is needed to keep the internal clock ticking, there is not really any need in changing the dependency of BIOS settings on a battery.
  3. jobeard

    jobeard TS Ambassador Posts: 11,161   +986

    POST: Power On Self Test. It's purely a hardware test, not dependent upon anything installed and runs directly from the BIOS. It detects keyboard, mouse, hd attachments and will react (usually with beep codes) if there are issues. As it can detect memory installed, it could not be run therein :)
  4. rodion15

    rodion15 TS Booster Topic Starter Posts: 147

    Thanks for your answer. I had the idea it loaded into RAM first. Not so. Thanks.

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