应该是效率,看Andrew S.Tanenbaum (Minix开发者)的《结构化计算机组成》或者John L. Hennessy(Mips提出者)和David A. Patterson(Risc提出者)《计算机体系结构:一种量化的研究方法》。我觉得从体系结构理解比较好,讨论在软件层的影响又是另外一回事了,前为因后为果,不能把影响说成原因
Regardless of the state of the $A directive, variables and typed constants are always aligned for optimal access. In the {$A+} state, execution will be faster.