为什么不能有MOV两个操作数为内存位置？ [英] Why can't MOV have both operands as memory locations?

问题描述

我读 MOV 指令不能有两个操作数的存储位置。

I read that MOV instruction cannot have memory locations for both its operands.

我爱： MOV [0012H]，[0016H] 不允许

为什么会这样？

和其它指令可以有两个操作数的存储位置？

And can other instructions have memory locations for both its operands?

推荐答案

它是当他们创造的CPU设计决策。更寻址有模式和多个指令，更大（在重新present指令所需的比特数计）的指令得到。和更大的指令需要更长的时间从内存中获取。

It's was a design decision when they created the CPU. More addressing modes you have and more instructions, larger (in terms of number of bits required to represent instruction) the instructions get. And larger instruction take longer to fetch from memory.

在换句话说，X86指令集是不是正交。这不一定是坏事，至少不是现在，该程序集code的只有非常有限的量写入。

In other words, x86's instruction set is not orthogonal. It is not necessarily bad, at least not now, that only very limited amount of assembly code is written.

一些其它的CPU（例如MC680xx在同一个时代设计的）可以做到这一点。

Some other CPUs (for example MC680xx designed in same era) can do that.

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