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How can I boot from an external hard drive?

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migrated from stackoverflow.com Dec 10 '09 at 12:47

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2 Answers

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You need to enter the BIOS of your computer and select USB as first boot device.

Very often, the BIOS is entered by pressing a key at the very beginning of the boot sequence, right after having powered the computer on:

  • F1
  • F2
  • ESC
  • DEL
  • SUPPR (on French keyboards)
  • (refer to the documentation of your sytem...)

Once you're in the BIOS, you can configure the boot order: for instance try to boot from floppy first, then cdrom/dvdrom, then hard-drive... The boot order is stored in the BIOS remains the same every time the computer starts.

As suggested in other answers and comments, some BIOS allow you to press a key (F12 for instance) that will bring you a one shot boot menu: the purpose of this menu is to let you exceptionally boot from another device.

If you exceptionally want to boot from an USB hard-drive, you're likely to want to bring the boot menu up. If you want to always boot from an USB hard-drive that remains plugged to your computer you're likely to change the boot order in your BIOS.

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I took the liberty to edit and give a more elaborate answer after having read the opinions in other comments – Gregory Pakosz Dec 10 '09 at 19:47
Great summary Gregory. Though it may be obvious to some of us, this is all true after the external hard drive has already been made bootable with the proper boot and/or system files. In other words, a drive previously used for storage purposes only (that does not have boot/system files) is not yet bootable. – ralford Dec 10 '09 at 20:06
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up vote 1 down vote

or open the boot device menu (most manufacturers use F12 during the POST screen, others may use ESC or a combination) and choose the device you want to from.

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works for DELL computers only? – Gregory Pakosz Dec 10 '09 at 13:39
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@gregory pakosz: nah, plenty of BIOSes include a boot device menu. not all are accessed with F12; check your system documentation. – quack quixote Dec 10 '09 at 14:08
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not only Dell, Fujitsu Siemes is the same, and many others too. ASUS is using the ESC key. – Molly7244 Dec 10 '09 at 17:20
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well, i'd say, F12 is more commonly used as key to bring up the boot selection menu than ESC. – Molly7244 Dec 10 '09 at 17:52
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+1 Confirmed. This is also the case for my machine, a custom build with an Asus A8R32 Mobo, my BIOS has a "Press F8 to open BBS Menu" warning which brings up the Boot Device Selection screen. This is much more useful than permanently changing the boot device as my BIOS gets more than a bit stupid when bios configured boot devices vanish. – Mokubai Dec 10 '09 at 19:12
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