指实现后台处理。所谓后台处理是指非联机处理，或者说不是直接和计算机连接起来而进行联机操作。优先级高的程序先于特定的后台作业执行。
Performing background processing which is not on-line or directly connected to the computer for on-line operation. High priority programs take precedence over specific background jobs.
一种重要的处理过程，其中最高优先权处理任务常常由具有优先度的实时任务形成，经过使用中断而进入较低优先权任务或后台处理任务。
An important processing procedure in which top-priority processing most often results from real-time entries which usually have precedence, through the use of interrupts into lower-priority or background processing.
