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I have a hard drive with system and sometimes I want to boot from an USB flash drive.

How to change settings of booting correctly so that:

  1. Boot from hard drive if there no flash drive.
  2. Boot from flash drive if there is flash drive in USB port.

Is it possible?

After each time when I free usb port and reuse this port again, settings are reset.

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What settings you are using currently? As I have set the USB and then HDD in boot priority so when USB plugged in it boots from it and when not then my system HDD is default for that. – avirk Nov 12 '12 at 7:40
Besides what avirk and takada said, depending on your BIOS a key like F10 pressed during bootup should display a boot menu where you can select the boot device you want. This allows you to change your boot device temporarily without making a permanent change in the BIOS. – Karan Nov 12 '12 at 17:55
up vote 2 down vote accepted

Earlier, BIOS allowed you to set the USB drive higher than the hard drive. Now, most new BIOS programs remove the USB drive from the list if it is not detected at bootup.

You can enable the boot-up password. This will give you enough time fix a USB drive if need be.

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You should have something like this on your bios screen under Boot Menu or something:

First Boot DEVICE     [USB-HDD]
Second Boot Device    [HDD] 
Third Boot Device     [CDROM] 

You can set the first boot device to be a USB-HDD. And the second boot device as the HDD where your OS resides.

This should accomplish your requirements of loading from HDD when there's no usb stick and vice versa.

Good luck!

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