I've installed Windows 8 on a machine (Lenovo X220 laptop) with Ubuntu 12.10 already installed on another disk.
I am guessing that Windows 8 has convinced the laptop to switch to UEFI boot (rather than the BIOS boot that was there previously) as the Lenovo splash screen on startup now no longer has the options to interrupt the boot process (for example, to choose the boot drive). Interestingly, I can interrupt the boot process and drop into the BIOS or choose a different boot drive if I restart the machine, but not from a cold boot.
Previously I had Windows 7 on one drive (mSATA SSD; listed in Linux as
/dev/sdb; first preference in the BIOS for booting) and Ubuntu on the other drive (SATA HDD listed in Linux as
/dev/sda). I had the Windows bootloader installed on
sdb, and GRUB installed on
sda, and I would choose which OS to boot by choosing the boot drive in the BIOS rather than through a bootloader menu. I can still do this (to load Linux) if I manage to get into the BIOS boot menu - GRUB is booting via the BIOS, but Windows is booting via UEFI.
So I would ultimately like to have both Linux and Windows boot by UEFI and have the option of choosing which one through a menu of some sort. How can I retrospectively get Linux booting from UEFI, and how would I get a menu happening?