How could a system be designed to allow a choice of operating systems from which to boot? What would the bootstrap program need to do?

This question wants us to assume that we have two or three various operating systems installed on our computer's hard disk. When you boot your machine, the boot manager program will make necessary calculations and choose to boot into the OS that has been set as a priority. However, since the boot managers are designed to offer the user with the list of OS available to boot into, the user can make these selections manually. By default, boot managers have to be stored at particular locations of the hard drive and get the recognition when the system boots up. The bootstrap program comes in when it wants to locate the kernel into RAM and execute it and start the OS.