中央處理單元（central processing unit）簡稱CPU，以被稱為中央處理器。一般由邏輯運(yùn)算單元、控制單元和存儲單元組成。在邏輯運(yùn)算和控制單元中包括一些寄存器，這些寄存器用于CPU在處理數(shù)據(jù)過程中數(shù)據(jù)的暫時保存， 簡單的講是由控制器和運(yùn)算器二部分組成.
CPU主要的性能指標(biāo)有：
1.主頻
主頻也叫時鐘頻率，單位是MHz，用來表示CPU的運(yùn)算速度。CPU的主頻＝外頻×倍頻系數(shù)。很多人認(rèn)為主頻就決定著CPU的運(yùn)行速度，這不僅是個片面的，而且對于服務(wù)器來講，這個認(rèn)識也出現(xiàn)了偏差。至今，沒有一條確定的公式能夠?qū)崿F(xiàn)主頻和實(shí)際的運(yùn)算速度兩者之間的數(shù)值關(guān)系，即使是兩大處理器廠家Intel和AMD，在這點(diǎn)上也存在著很大的爭議，我們從Intel的產(chǎn)品的發(fā)展趨勢，可以看出Intel很注重加強(qiáng)自身主頻的發(fā)展。像其他的處理器廠家，有人曾經(jīng)拿過一快1G的全美達(dá)來做比較，它的運(yùn)行效率相當(dāng)于2G的Intel處理器。

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所以，CPU的主頻與CPU實(shí)際的運(yùn)算能力是沒有直接關(guān)系的，主頻表示在CPU內(nèi)數(shù)字脈沖信號震蕩的速度。在Intel的處理器產(chǎn)品中，我們也可以看到這樣的例子：1 GHz Itanium芯片能夠表現(xiàn)得差不多跟2.66 GHz Xeon/Opteron一樣快，或是1.5 GHz Itanium 2大約跟4 GHz Xeon/Opteron一樣快。CPU的運(yùn)算速度還要看CPU的流水線的各方面的性能指標(biāo)。
當(dāng)然，主頻和實(shí)際的運(yùn)算速度是有關(guān)的，只能說主頻僅僅是CPU性能表現(xiàn)的一個方面，而不代表CPU的整體性能。
2.外頻　外頻是CPU的基準(zhǔn)頻率，單位也是MHz。CPU的外頻決定著整塊主板的運(yùn)行速度。說白了，在臺式機(jī)中，我們所說的超頻，都是超CPU的外頻（當(dāng)然一般情況下，CPU的倍頻都是被鎖住的）相信這點(diǎn)是很好理解的。但對于服務(wù)器CPU來講，超頻是絕對不允許的。前面說到CPU決定著主板的運(yùn)行速度，兩者是同步運(yùn)行的，如果把服務(wù)器CPU超頻了，改變了外頻，會產(chǎn)生異步運(yùn)行，（臺式機(jī)很多主板都支持異步運(yùn)行）這樣會造成整個服務(wù)器系統(tǒng)的不穩(wěn)定。

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The central processing unit (central processing unit) is referred to as the CPU. It is generally composed of logical operation unit, control unit and storage unit. The logical operation and control unit includes some registers, which are used for the temporary storage of data in the process of data processing by the CPU, which is simply composed of two parts: controller and arithmetic.
The main performance indicators of the CPU are:
1. Main frequency
The main frequency is also called the clock frequency, and the unit is MHz, which is used to represent the computing speed of the CPU. CPU main frequency = external frequency x frequency multiplier factor. Many people think that the frequency determines the speed of the CPU, which is not only one-sided, but also for the server, this understanding has also been biased. So far, there is no definite formula to achieve the numerical relationship between the frequency and the actual computing speed, even the two major processor manufacturers Intel and AMD, there is a great dispute in this point, we from the development trend of Intel products, we can see that Intel pays great attention to strengthen the development of their own frequency. Like other processor manufacturers, someone once took a fast 1G United States to compare, its operating efficiency is equivalent to 2G Intel processors.
Therefore, the frequency of the CPU is not directly related to the actual computing power of the CPU, and the frequency represents the speed of the digital pulse signal oscillation in the CPU. We can also see examples of this in Intel’s processor products: the 1 GHz Itanium chip can perform almost 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. The computing speed of the CPU also depends on the performance indicators of all aspects of the CPU pipeline.
Of course, the frequency and the actual computing speed is related, can only say that the frequency is only one aspect of the CPU performance, and does not represent the overall performance of the CPU.
2. External frequency External frequency is the base frequency of the CPU, and the unit is also MHz. The external frequency of the CPU determines the running speed of the entire motherboard. To put it plainly, in desktop computers, what we call overclocking is the external frequency of the super CPU (of course, under normal circumstances, the frequency of the CPU is locked) I believe this is very well understood. But for the server CPU, overclocking is absolutely not allowed. Previously said that the CPU determines the speed of the motherboard, the two are synchronous operation, if the server CPU overclocked, change the external frequency, will produce asynchronous operation, (many desktop motherboards support asynchronous operation) this will cause the instability of the entire server system.

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