The BIOS provides the basic functions needed to boot your machine and to allow your operating system to access your hardware. Your system provides a BIOS setup menu, which is used to configure the BIOS. To enter the BIOS setup menu you have to press a key or key combination after turning on the computer. Often it is the Delete or the F2 key, but some manufacturers use other keys. Usually upon starting the computer there will be a message stating which key to press to enter the setup screen. Within the BIOS setup menu, you can select which devices shall be checked in which sequence for a bootable operating system. Possible choices usually include the internal harddisks, the CD/DVD-ROM drive and USB mass storage devices such as USB sticks or external USB harddisks. On modern systems there is also often a possibility to enable network booting via PXE. Depending on the installation media (CD/DVD ROM, USB stick, network boot) you have chosen you should enable the appropriate boot devices if they are not already enabled. Most BIOS versions allow you to call up a boot menu on system startup in which you select from which device the computer should start for the current session. If this option is available, the BIOS usually displays a short message like press F12 for boot menu on system startup. The actual key used to select this menu varies from system to system; commonly used keys are F12, F11 and F8. Choosing a device from this menu does not change the default boot order of the BIOS, i.e. you can start once from a USB stick while having configured the internal harddisk as the normal primary boot device. If your BIOS does not provide you with a boot menu to do ad-hoc choices of the current boot device, you will have to change your BIOS setup to make the device from which the &d-i; shall be booted the primary boot device. Unfortunately some computers contain buggy BIOS versions. Booting &d-i; from a USB stick might not work even if there is an appropriate option in the BIOS setup menu and the stick is selected as the primary boot device. On some of these systems using a USB stick as boot medium is impossible; others can be tricked into booting from the stick by changing the device type in the BIOS setup from the default USB harddisk or USB stick to USB ZIP or USB CDROM. In particular if you use an isohybrid CD/DVD image on a USB stick (see ), changing the device type to USB CDROM helps on some BIOSes which will not boot from a USB stick in USB harddisk mode. If you cannot manipulate the BIOS to boot directly from a USB stick you still have the option of using an ISO copied to the stick. Boot &d-i; using and, after scanning the hard drives for an installer ISO image, select the USB device and choose an installation image.