该程序利用内存模拟SPOOLing输出系统。有三个用户进程要求输出符号串（只传送到输出井），SPOOLing进程负责实际的输出工作-It uses memory simulation SPOOLing output system. There are three user process requires the output symbol string (only sent to the output shaft), SPOOLing process responsible for the actual output work