When a system is configured to allow booting to different operating systems at startup, what is this called?

The term dual-boot has come to mean the ability to boot between two or more operating systems at startup.

Explanation:

A dual boot is when you run two operating systems on one computer at the same time. This can be any combination of operating systems, for example, Windows and Mac, Windows and Linux or Windows 7 and Windows 10.

'Booting' is normally used interchangeably with 'starting' or 'powering on' when referring to computers. But in regard to dual-booting, the term specifically refers to something called the 'boot manager', a tiny program managed by the motherboard.

When you turn on a PC, the power supply unit (PSU) initially powers up the motherboard, which manages and holds together all your other computer components. If you've ever seen a black screen with text and possibly logos on it after you've started your PC, but before it gets to the Windows login screen, this is the motherboard letting you know it is on.

The motherboard scans all the different components that are connected to it, such as graphics cards, optical drives (CD or DVD) and disk drives. Once the motherboard has established the state of your hardware, it knows that you will most likely want to boot into an operating system. To do this, the motherboard passes over the drive information to the boot manager.

Boot managers are software that can run on your computer before an operating system is loaded. Their task is to locate operating systems on your drives and start-up whichever you would like to use. Most people with a Windows PC or Mac may never have seen the boot manager on their computer - it simply assumes that since it can only find one operating system, this is the one you want to use.