Multiuser operating systems must include several features多用户操作系统必须包括的几个特点)
．An authentication mechanism for verifying the user identity.(一个辨别用户身体的认证系统)
．A protection mechanism against (buggy user求助) programs that could block other applications running in the system
一个保护系统，来防止buggy user的程序，阻断系统应用的运行．
．Ａ protection mechanism against malicious user programs that could interfere with,or spy on,the activity fo other users
一个保护机制，来防止恶意用户的程序感染或窥探其他用户的活动．
．An accounting mechanism that limits the amount of resource units assigned to each user
一个统计系统，来限制大量的资源单元分给个用户．
In order to ensure safe protection mechanisms ,operating systems must make use of the harware protection associated with the CPU privileged mode.
为了确保保护机制的安全，操作系统必须利用硬件保护和ＣＰＵ特权模式相结合的方法来在到保护目的．
otherwise,a user program would be able to directly access the system circuitry and overcome the imposed bounds
否则的话，用户程序将能直接访问系统电路并穿透强制界限．
Unix is a multiuser system that enforces (the hardware protection of system resources.怎么译好？)
Unix是一个多用户操作系统，它强制保护系统资源．the hardware 不知怎么放才好．
多用户操作系统必须包括的几个特点)