存储一个32位数0x12345678到1000H～1003H四个字节单元中，若以小端模式存储，则1000H存储单元的内容为______。
- A.0x12
- B.0x21
- C.0x78
- D.0x87
正确答案及解析
正确答案
解析
本题考查计算机存储系统的基础知识。大端模式是指数据的高位保存在内存的低地址中，而数据的低位则保存在内存的高地址中，地址由小向大增加，而数据从高位往低位放。小端模式是指数据的高位保存在内存的高地址中，而数据的低位则保存在内存的低地址中，这种存储模式将地址的高低和数据位权有效地结合起来，高地址部分权值高，低地址部分权值低，和我们的逻辑方法一致。计算机系统中以字节为单位，即每个地址单元都对应着一个字节(8bit)。但是在C语言中除了8bit，的char之外，还有16bit的short型，32bit的long型(要看具体的编译器)，另外，对于位数大于8位的处理器，例如16位或者32位的处理器，由于寄存器宽度大于一个字节，那么必然存在着一个如何将多个字节安排的问题。因此就导致了大端存储模式和小端存储模式。例如一个16bit的short型x，在内存中的地址为0x0010，x的值为0x1122，那么0x11为高字节，0x22为低字节。对于大端模式，就将Ox11放在低地址中，即0x0010中，0x22放在高地址中，即0x0011中。小端模式则刚好相反。我们常用的X86结构是小端模式，而KEIL C51则为大端模式。很多的ARM，DSP都为小端模式。有些ARM处理器还可以由硬件来选择是大端模式还是小端模式。
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