A time clock by which the executive keeps track of time. At every RTC interrupt, the interrupt service routine returns control to the executive, which checks to see if a higherpriority device is seeking execution or if a program wants to be turned “on”.; 執(zhí)行程序用來對時間進行跟蹤的一種時鐘，在每一個RTC中斷處，由中斷 服務程序把控制返回給執(zhí)行程序，執(zhí)行程序檢驗是否有較高優(yōu)先級的設備在請求執(zhí)行，或是 否要求“打開”某個程序。