On x86 platforms, the machine hardware is initialized at boot time by the NTLDR. To initialize the video hardware, NTLDR makes a BIOS call to set the video adapter in 80x50, 16-color, alphanumeric mode. It then clears the screen and displays the Boot Manager messages.
On RISC platforms, the entire machine, including video hardware, is initialized by the OSLOADER, which programs an appropriate alphanumeric mode to display the Boot Manager information.