org 07c00h ; P
mov ax, cs
mov ds, ax
mov es, ax
call STR; Call display string routine
JMP $;
> BBSTR :
mov ax, BootMessage
mov bp, ax; ES:BP = string address
mov cx, 16; CX = string length
mov ax, 01301h; AH = 13, AL = 01h
mov bx, 000ch; BL = 0Ch, highlighted)
mov dl, 0
int 10h; BootMessage: db “Hello, OS world!” BootMessage: db “Hello, OS world!
times 510-($-$$) db 0 ; Fill the remaining space so that the generated binary code is exactly 512 bytes
dw 0xaa55; End flag

To compile into an executable program under Linux, use the command:
Nasm-f ELF pmboot.asm -o pmboot.bin

Compiler error:

The boot. The asm: 1: error: parser: instruction is expected

Use the command nasm pmboot.asm -o pmboot.bin without error.