https://en.wikipedia.org/wiki/Clock_rate
The clock rate typically refers to the frequency at which a chip like a central processing unit (CPU), one core of a multi-core processor, is running and is used as an indicator of the processor's speed. It is measured in clock cycles per second or its equivalent, the SI unit hertz (Hz). The clock rate of the first generation of computers was measured in hertz or kilohertz (kHz), but in the 21st century the speed of modern CPUs is commonly advertised in gigahertz (GHz). This metric is most useful when comparing processors within the same family, holding constant other features that may impact performance. Video card and CPU manufacturers commonly select their highest performing units from a manufacturing batch and set their maximum clock rate higher, fetching a higher price.
https://zh.wikipedia.org/wiki/时钟频率
时钟频率（又译：时钟频率速度，英语：clock rate）是指同步电路中时钟的基础频率，它以“每秒时钟周期”（clock cycles per second）来度量，量度单位采用SI单位赫兹（Hz）。例如，来自晶振的基准频率通常等于一个固定的正弦波形，则时钟频率就是这个基准频率，电子电路会为数字电子设备将它转化成对应的脉冲方波。需要补充一点的是，“速度”作为矢量不应与标量“频率”相混淆，所以使用“时钟速度”来描述这个概念是用词不当的。
在单个时钟周期内（现代非嵌入式微处理器的这个时间一般都短于一纳秒）逻辑零状态与逻辑一状态来回切换。 由于发热和电气规格的限制，周期里逻辑零状态的持续时间历来要长于逻辑一状态。
中央处理器（CPU）制造商常为时钟频率较高的CPU定额外的高价。就某个CPU来说，时钟频率是在生产环节的最后通过实测测定的。通过了特定测试标准的CPU会被标上这个标准相应的时钟频率，如1.5GHz。而当一个CPU没有通过较高时钟频率一级的测试但通过了较低一级的测试时，它会被标上一个较低的时钟频率。例如某个CPU未通过1.5GHz时钟频率的测试却通过了1.33GHz那一级的，它就会被标为1.33GHz，并且相对于时钟频率为1.5GHz的CPU，它的卖价要低。[1][2]