保护模式中的地址转换前缀代码

[who_1111]

最近在学习保护模式，发现在保护模式下面调用寄存器传送数据的时候，会有以下代码：

DB 66h ; PUSHING ALL REGS AS 32-BIT ONES
PUSH DS
DB 66h
PUSH ES
DB 66h
PUSH FS
DB 66h
PUSH GS

这个DB 66H查了一下，说是地址转换前缀代码，可是之后的一篇程序代码里面，定义的却是DB 67H，请问这个是怎么定义的呢？
db 67h ; use 32-bit registers in 16-bit code
rep movsb
pop es
retn

总之，就是DB 66H; DB 67H是怎么定义的？两个有什么区别呢？
谢谢！

[xtdumpling]

请看这个帖子:http://topic.csdn.net/u/20080724/01/57fc554d-ac2b-43fc-ab57-432c7057983b.html

[s393658806]

学一下

[Guilty]

mov eax, [bx] //66
mov ax, [ebx] //67

[who_1111]

谢谢！

[who_1111]

The 80386 has two instruction prefixes that allow mixing of 32-bit and
16-bit operations within one segment:
● The operand-size prefix (66H)
● The address-size prefix (67H)

These prefixes reverse the default size selected by the D-bit. For example,
the processor can interpret the word-move instruction MOV mem, reg in any of
four ways:
● In a USE32 segment:
1. Normally moves 32 bits from a 32-bit register to a 32-bit
effective address in memory.
2. If preceded by an operand-size prefix, moves 16 bits from a 16-bit
register to 32-bit effective address in memory.
3. If preceded by an address-size prefix, moves 32 bits from a 32-bit
register to a16-bit effective address in memory.
4. If preceded by both an address-size prefix and an operand-size
prefix, moves 16 bits from a 16-bit register to a 16-bit effective
address in memory.
● In a USE16 segment:
1. Normally moves 16 bits from a 16-bit register to a 16-bit
effective address in memory.
2. If preceded by an operand-size prefix, moves 32 bits from a 32-bit
register to 16-bit effective address in memory.
3. If preceded by an address-size prefix, moves 16 bits from a 16-bit
register to a32-bit effective address in memory.
4. If preceded by both an address-size prefix and an operand-size
prefix, moves 32 bits from a 32-bit register to a 32-bit effective
address in memory.

分享一下，这个资料还是不错的。