x86 - 为什么为 NASM 编写的这个“hello world”x86 引导加载程序代码在没有 [BITS 16] 和 [ORG 0x7C00] 指令的情况下工作？

Question

push word 0b800h
pop es
xor di, di
mov [es:di], word 441h
jmp $
times 510 - ($-$$) db 0
db 55h
db 0AAh

Answer 1

Because you are writing a flat binary without labels. NASM should default to 16-bit. Related to this is the fact that you have no addressing or labels - so no requirement to provide an [ORG ...] directive.