Those particular instructions are burned into cmos - they read (in plain english)
No, they aren't, the BIOS simply looks for a valid bootsector on the disk which is in the process of being booted. That bootsector contains the code needed to continue booting the operating system.

Anyway, that doesn't matter anymore as I have accomplished my purpose, I have written a bootsector and raw written it to a floppy.

Code:
[BITS 16]
[ORG 0]

jmp start

msg db 'Booting a shitty program$'

start:
        mov ax,0x7c0    
        mov ds,ax

        mov si, msg
        lodsb
        mov ah,0eh              ; output character on screen function
       mov bx,0007             ; bl value = attribute (back/foreground colour), not sure what bh does though...lol
       int 10h                ;BIOS interrupt
       ret
    
times 510-($-$$) db 0   ;we need to fill so the binary image will be 512 bytes
                        ;$ = start of instruction
                        ;$$ = start of program
dw 0xAA55       ;fills last 2 bytes with 0xAA55 which makes this a valid bootsector
                ;(the BIOS checks whether it ends with 0xAA55)
How come it only displays a 'B' instead of the entire string I want to print?