可编程间隔定时器（Programmable Interval Timer，PIT， 8253或8254模型），也叫做系统时钟，是一个非常有用的芯片，可以在一定时间间隔精确地产生中断。芯片本身有3个通道：通道0绑定到IRQ0，在可预知和规则的时间中断CPU；通道1特定于系统；通道2则连接到系统扬声器。就像你看到的一样，单个的芯片为系统提供了几个非常重要的服务。-Programmable Interval Timer (Programmable Interval Timer, PIT, 8253 or 8254 model), also known as the system clock, is a very useful chip in a certain time interval can be accurately generate an interrupt. Chip itself has three channels: channel 0 bound to IRQ0, and rules in the foreseeable time interrupt CPU　channel 1-specific systems　2-channel speaker connected to the system. As you see, like a single chip for the system provides several important services.