Each computer has a biggest installed memory ,in which,when there is insufficient space,some other uses must write out their residing program to the disk unit to create some free memory space.

• 每台计算机都有一个大的内存；当一个用户程序运行时空间不够；其他用户的驻留内存程序须写回磁盘单元；释放一些内存空间.