说明：  RTC的英文全称是Real-Time Clock,翻译过来是实时时钟芯片. RTC是PC主板上的晶振及相关电路组成的时钟电路的生成脉冲，RTC经过8254电路的变频产生一个频率较低一点的OS(系统)时钟TSC，系统时钟每一个cpu周期加一，每次系统时钟在系统初起时通过RTC初始化。8254本身工作也需要有自己的驱动时钟（PIT）。
(English name of the RTC Real-Time Clock, translated real-time clock chip RTC crystal and associated circuitry on the PC motherboard clock circuit to generate a pulse, the RTC after the 8254 circuit of variable frequency to produce a lower frequency of the OS(system) clock TSC, the system clock a cpu cycle plus one, each time the system clock in the system since the beginning of initialization through the RTC. The 8254 work also need to have their own drive clock (the PIT). )