Samsung ultrabook series 5 and 9 use F2 key to enter BIOS setup. Commercially, such ultrabooks come with Windows support having BIOS optimized to the use of Windows system. I mean, the boot phase is fast then you need to be fast either. However, the process is simple.
Turn on the ultrabook and press F2 key repeatdly. You should enter in BIOS setup by doing this. Having entered in BIOS, some steps must be done in order to get boot from USB possible (assuming you want to install a Linux OS by using a flashdrive). At the BIOS setup, the following sequence of steps must be done:
At Advanced Tab:
Fast BIOS Mode: Disabled AHCI Mode Control: Manual (Let be "Auto" just in case you wanna use dual boot with Windows) Set AHCI Mode: Disabled USB S3 Wake-up: Enabled
At Boot Tab:
Secure Boot: DisabledEnabled OS Mode Selection: UEFI and CSM OS (This option enables dual boot. No problem to do it with a single boot)
Still at Boot Tab: Select “Boot Priority Order” and press Enter key. It should show you a list of boot sources. Put USB HDD in the first. (Press F5 and F6 to move up and down). I put here, an example.
1. USB HDD: 2. SATA HDD: 3. SATA CD: ...
Hope I helped you,