一个字的大小为什么是2字节

one sees that word is defined to be 2 bytes (or 16 bits). It was
given this meaning when the 8086 was first released. When the 80386 was
developed, it was decided to leave the definition of word unchanged, even
though the register size changed.

1.2. COMPUTER ORGANIZATION 5
word 2 bytes
double word 4 bytes
quad word 8 bytes
paragraph 16 bytes
Table 1.2: Units of Memory

一个字的大小就是寄存器的大小，当时定义word的时候，寄存器大小是16位 【8086】，后来寄存器大小发生变化后，word的大小就没有发生改变。

pc汇编