Main frequency is also called clock frequency, the unit is megahertz (MHz) or gigahertz (GHz), used to indicate the CPU computing, processing data speed.
CPU main frequency = external frequency x frequency multiplier coefficient. A lot of people think that the main frequency determines the running speed of the CPU, which is not only one-sided, and for the server, this understanding also appeared deviation. So far, there is no certain formula can realize the numerical relationship between the main frequency and the actual operation speed, even the two major processor manufacturers Intel (Intel) and AMD, there is a great controversy on this point, from the development trend of Intel products, we can see that Intel is very focused on strengthening the development of its own main frequency. Like other processors, a 1GHz All-American processor has been compared to a 2GHz Intel processor.
There is a certain relationship between the main frequency and the actual computing speed, but it is not a simple linear relationship. So, the main frequency of CPU and CPU actual computing ability is not directly concerned, the main frequency indicates the speed of oscillation of digital pulse signal in CPU. Examples can also be seen in Intel processors: the 1 GHz Itanium chip is much as fast as the 2.66 GHz Xeon/Opteron, or the 1.5 GHz Itanium 2 is about as fast as the 4 GHz Xeon/Opteron. CPU operation speed also depends on CPU pipeline, bus and so on various performance indicators.
The main frequency is related to the actual computing speed. It can only be said that the main frequency is only an aspect of CPU performance, and does not represent the overall performance of the CPU.
The external frequency is the reference frequency of the CPU, in MHz. The external frequency of CPU determines the operation speed of the whole motherboard. Generally speaking, in desktop computers, the overclocking refers to the external frequency of the superCPU (of course, under normal circumstances, the CPU is locked) I believe this is very easy to understand. But for the server CPU, overclocking is absolutely not allowed. In front of the CPU determines the motherboard running speed, the two are synchronous operation, if the server CPU overfrequency, change the external frequency, will produce asynchronous operation, (desktop many motherboards support asynchronous operation) it will cause the instability of the whole server system.
At present, the vast majority of computer systems, the external frequency and the main board front-end bus is not synchronous speed, and the external frequency and front-end bus (FSB) frequency is easily confused.