Microsoft will allow companies that manufacturer Windows 10 devices to force UEFI Secure Boot. This can prevent users from easily installing other operating systems on the same device.
During a presentation on WinHEC, Microsoft announced that the switch to turn Secure Boot on and off with Windows 8 still is obliged, but with Windows 10 it will be optional. Devices with Microsoft's upcoming operating system will be shipped with Secure Boot on and companies can decide whether they offer a possibility to turn off Secure Boot. Once Secure Boot is turned on, alternative operating systems, like Linux, require a cryptographic signature to boot the PC.
This makes it harder for users to install alternative operating systems because the in many cases operating systems don't have the required digital signature. Mainly because the validness of the keys can only be programmed by the manufacturer. How big of an issue this will be really depends on whether companies decide to ship their devices with the Secure Boot switch, currently not much is known about that yet. The new rules only apply to desktops, on Windows 10 for smartphones it's not allowed to turn off Secure Boot.
Microsoft also announced on WinHEC that Windows 10 will get support for being an USB host on smartphones and the reversible Type C connector of USB 3.1. The operating system is still in beta stage and should be released later this year.
