In other words, SOFTWARE interrupts always occur at the beginning of an instruction execution cycle.
换句话说，软件中断常常在指令运行周期的开始发生。
In an SISD architecture there is a single instruction cycle; operands are fetched serially into a single processing unit before execution.
在单指令流单数据流结构中，有单一的指令周期，在执行前，单个处理机按序取操作数。
At the beginning of an instruction execution cycle.
指令运行周期的开始发生。
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