A use case is a singletask, performed by the end user of a system, that has some useful outcome.
用例是单个任务，能产生有用的结果，由系统最终用户执行。
2
In a single processor computer the CPU can execute one task at a time, but the Operating System manages which task should access the CPU.
在一个单处理器计算机中，CPU一个时刻只能执行一个任务，由操作系统管理哪一个任务使用CPU。
3
For those busy person that run multiple applications in a single PC system, it is quite common to expand the taskbar space just to cater for all the running applications for easy task switching.