lexon wrote:It was my understanding that the PC bios would not allow a different OS.
No, that's absolutely false.
First, BIOS != UEFI. BIOS is the old 16-bit firmware for PCs. It's essentially gone now, but manufacturers are continuing to refer to their new UEFI firmware as "BIOSes," probably because a significant fraction of their customers are familiar with the term and because the UEFI fits the same space in the software stack. The generic term for both BIOS and UEFI, though, is "firmware."
That said, most modern UEFI implementations include something called the Compatibility Support Module (CSM), which is a BIOS emulation layer that enables the computer to boot BIOS-based OSes. Thus, a modern UEFI system can work very much like a BIOS-based computer. You get a few advantages when you boot in UEFI mode, though, like a potentially quicker boot time and a different set of boot loaders. I'm getting a bit off point, though....
BIOS has never been restricted to a single OS. By its design, it would be virtually impossible to limit it in that way -- at least, not and have it remain recognizably a BIOS. UEFI is also not restricted to a single OS; however, it supports a feature called
Secure Boot that enables whoever set up the computer's firmware to include a set of cryptographic public keys that can be used to authenticate a boot loader. If the boot loader isn't signed with the private key matching one of the included public keys, then the firmware can refuse to launch the boot loader. This
can be used to lock a computer into a single OS -- but note the emphasis on
can. There's no requirement that a computer be configured in such a restrictive way. In fact, Microsoft's certification requirements for Windows 8 desktop and laptop computers specify that users must have the ability to reconfigure the Secure Boot keys on x86-64 computers, or disable Secure Boot altogether. Thus, there is a practical requirement that x86-64 desktop and laptop computers can
not be locked into a single OS.
The story takes another twist on ARM-based computers, though; on that platform, Microsoft requires that Secure Boot can
not be disabled or reconfigured by the user. Thus, at the moment and AFAIK, ARM computers that ship with Windows 8 are effectively locked into running Windows 8. This could change in the future, though; Microsoft offers a signing service that enables developers to get programs signed with Microsoft's key. This has already been done for x86-64 boot loaders (to simplify things for users), but to the best of my knowledge not for any ARM boot loader. In principle it could be done; it's just that the ARM market is so small, and is currently so dominated by non-Windows devices, that nobody has yet bothered to try. If and when somebody gets an ARM version of
Fedora's shim or
the Linux Foundation's PreBootloader signed, though, even Windows 8 ARM devices will become capable of booting Linux.