windows - How do computers boot?

05
2014-04
  • Questioner

    How does a computer boot and how does this differ for Windows, Linux and other OSes?

    • Answers
  • enter image description here Tom Wijsman

    What are the several steps the computer does during boot on a BIOS PC?

    When you power your computer on, the processor will start the BIOS boot program.

    The BIOS phase

    If everything goes well; the computer will look for a video card, execute a power-on self test and show all the useful information about this and the next steps on the BIOS startup screen:

    enter image description here

    You will see the computer perform a memory test, detect any storage devices connected and depending on BIOS you might also see a second screen showing you an inventory of everything the computer has detected through common interfaces like COM/LTP/USB/PnP/...

    So, as your computer is now ready it will now follow the boot sequence to determine which drive to boot from, it will look through the master boot records until a boot partition has been found, in which case the computer will start to boot the operating system by executing the boot record.

    The Boot Loader phase

    Back in these days, we had to boot DOS and Unix which we could boot in a direct way. Nowadays, the boot procedure is subject to limits. So at this point we'll have to let a small boot loader load the larger boot procedure. The small boot loader will set up important stuff the boot procedure needs and will load the essential parts of boot procedure into memory.

    This leads on to booting Windows, booting Linux or ...

  • Area 51

    What Microsoft has to say about it

    http://technet.microsoft.com/en-us/library/cc750074.aspx


    • Related Question

    How to get computer to boot from Windows cd after LINUX installation
  • REA_ANDREW

    I have a computer which has had a previous installation of linux on, and after various attempts to format the harddrive, I cannot get the bios to recognize the windows xp cd as a boot device. Linux has taken over the bios. Can someone give me advice how I can get the computer to boot from the cd so I can get windows back on there. There is currently a grub console which appears now after every boot up. But unfortuntely I am clueless.

    Andrew

    UPDATE:

    I have the dvd set as the boot device.

    I have tested the boot dvd on another computer and it works fine

    If i select F8 for the boot menu then i get the cent os choice with one option. I am now on the GRUB Command line, not knowing a thing.


    • Related Answers
  • harrymc

    Linux cannot have flashed your BIOS, unless some pretty weird operations were done on this computer. Under normal circumstances, either the CD is not set in the BIOS as the first boot device, or the XP boot cd is faulty, or the CD drive itself is faulty.

  • Will

    When the computer starts the boot sequence pres the button to enter the BIOS set-up (del, or one of the F keys typically).

    Soemwhere in the BIOS you should be able to choose the boot sequence and/or what drives are bootable (HD, USB, Cd/DVD). Ensure that you can boot off the CD AND that it is first in the sequence. This should allow you to boot off the CD.

    A normal Linux installation will not mess with you BIOS.

  • Journeyman Geek

    have you checked if your cd/dvd unit can read cd's? what happens when your in linux and you put xp cd in the drive? can the system read it? if it has problems reading it then your cd unit needs cleaning. is original cd or you have burned it? try burning at lowest speed and use more reliable media.

  • 8088

    If you have Ubuntu 9.04 you can install and format your hard drive, then boot from a Windows XP CD and delete the Linux MBR from your drive.

    You can then install Windows with no problems.