# 4大Segment的暫存器組合 (參考WIKI x86 Assembly)
CS:IP (CS is Code Segment, IP is Instruction Pointer) points to the address where the processor will fetch the next byte of code.
SS:SP (SS is Stack Segment, SP is Stack Pointer) points to the address of the top of the stack, i.e. the most recently pushed byte.
DS:SI (DS is Data Segment, SI is Source Index) is often used to point to string data that is about to be copied to ES:DI.
ES:DI (ES is Extra Segment, DI is Destination Index) is typically used to point to the destination for a string copy, as mentioned above.
# FLAG register:
Overflow(bit 11)/Direction(bit 10)/Interrupt(bit 9)/Sign(bit 7)/Zero(bit 6)/Auxiliary Carry(bit 4)/Parity(bit 2)/Carry(bit 0)
# 操作Flag register 的指令:
STD ;Set Direction Flag (STD sets the direction flag to 1, causing all subsequent string operations to decrement the index registers, (E)SI and/or (E)DI, on which they operate.)
CLD ;Clear Direction Flag
STC ;Set Carry Flag
CLC ;Clear Carry Flag
CLI ;Clear Interrupt Flag
STI ;Set Interrupts
# 一些在Bios常使用的指令
PUSHA ;(PUSH ALL)：PUSH ax,cx,dx,bx,sp,bp,si,di
PUSHAD ;Push EAX, ECX, EDX, EBX, original ESP, EBP, ESI, and EDI PUSHF ; Save the CPU flags on the stack.
POPF ;Restore the CPU flags from the stack.
POPA ;(POP ALL)：POP di,si,bp,sp,bx,dx,cx,ax
RET ;副程式結束，返回，即 pop ip
RETF ;遠程副程式結束，返回，即 pop cs 然後 pop ip
MOVSB ;Move byte at address DS:(E)SI to address ES:(E)DI.
# 標記與跳躍 @F 或 @B (這段是參考小木偶的網頁，感謝他)
除了高階的流程控制之外，MASM 6.x 還接受一種特殊標記，@@:。這種標記是做為跳躍指令的目的地，要用 @@: 做為目的地的跳躍指令，必須配合 @f 或 @b 使用，前者是指往前跳躍，後者是往後跳躍，它們都只向前或向後跳躍到第一個 @@: 標記處。
例如有一個程式片段，是用來使一個佔用 16 個位元組的 key_buffer 陣列所有元素填上 0，一般會這樣寫：
+ mov cx,16
+ lea si,key_buffer
+ next: mov byte ptr ss:[si],0
+ inc si
+ loop next
如果 next: 標記只有此處用到，那麼便可以用 @@: 代替，變成下面的程式：
+ mov cx,16
+ lea si,key_buffer
+ @@: mov byte ptr ss:[si],0
+ inc si
+ loop @b
