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Home > How To > What is the external frequency?
What is the external frequency?

What is the external frequency?

By  Brietta Boatman 2020-01-06 301 179

In the early computer, the speed of synchronous operation between the memory and the motherboard is equal to the external frequency. In this way, it can be understood that the external frequency of CPU is directly connected with the memory, realizing the synchronous running state between the two. For the current computer system, the two can be completely different, but the meaning of the external frequency still exists. Most of the frequencies in the computer system are realized on the basis of the external frequency and multiplied by a certain multiple, which can be greater than 1 or less than 1.


When it comes to the external frequency of the processor, it is necessary to mention two concepts closely related to it: the frequency doubling and the main frequency, which is the clock frequency of the CPU, and the frequency doubling is the multiple of the ratio of the main frequency to the external frequency. The relationship between main frequency, external frequency and frequency doubling is as follows: main frequency = external frequency × frequency doubling.

In electronic technology, a pulse signal is a continuous pulse signal sent out continuously according to a certain voltage amplitude and a certain time interval. The time interval between the first pulse and the second pulse is called a period, while the number of pulses generated in a unit time (such as 1 second) is called frequency. Frequency is a measurement name that describes the number of pulses that a periodic cycle signal, including a pulse signal, appears in a unit of time; the standard unit of measurement of frequency is Hz (Hz). The system clock in the computer is a typical pulse signal generator whose frequency is quite accurate and stable.

Why should there be a clock in the computer system? The computer is a complex data processing system, in which CPU processes data according to certain instructions. Each time the instructions are executed, the arithmetic unit, register and controller inside the CPU must cooperate with each other. Although the instruction length is different each time, and there is more than one CPU internal unit involved in the operation, it can all be carried out synchronously according to the unified clock pulse. So the whole system can operate harmoniously and normally. And in addition to CPU in the computer, there are storage systems and display systems, etc., because these subsystems also need to use specific frequency clock signals for standard operation, so in the computer system, in addition to CPU main frequency and system clock, there are also clocks for ISA and PCI bus and AGP display interface, of course, the frequency of these clocks are lower than the system clock.


The difference between external frequency and front-end bus

External frequency and front-end bus (FSB) frequency are easily confused. The speed of the front-end bus refers to the speed of the bus between CPU and Beiqiao chip, which more substantially represents the speed of data transmission between CPU and the outside world. The concept of external frequency is based on the oscillation speed of digital pulse signal, that is to say, 100MHz external frequency especially refers to the digital pulse signal oscillating 10 million times per second, which more affects the frequency of PCI and other buses. The main reason why the two concepts of front-end bus and external frequency are easy to be confused is that for a long time before (mainly before the emergence of Pentium 4 and when Pentium 4 appeared), the front-end bus frequency is the same as the external frequency, so it is often directly called the front-end bus as external frequency, resulting in such a misunderstanding. With the development of computer technology, people find that the frequency of the front-end bus needs to be higher than the external frequency, so QDR (Quad Date Rate) technology or other similar technologies are used to achieve this purpose. The principle of these technologies is similar to the 2X or 4X of AGP. They make the frequency of the front-end bus become 2 times, 4 times or even higher than the external frequency. From then on, people began to pay attention to the difference between the front-end bus and the external frequency.

A CPU has only one external frequency by default, and the motherboard must be able to support this external frequency. Therefore, you must pay attention to this when choosing the motherboard and CPU. If the two do not match, the system will not work. In addition, many of the frequency doubling of CPU has been locked, so ultra-external frequency is often needed when overclocking. After the external frequency changes, many other frequencies of the system will also change, in addition to the CPU main frequency, front-end bus frequency, PCI and other interface frequencies, including the frequency of the hard disk interface will change, which may cause the system can not operate normally. Of course, some motherboards can provide locking various interface frequencies.

Set the standard external frequency of CPU

At present, the standard external frequency of CPU is only 66MHz, 100MHz and 133MHz (there are already 200MHz). Although the new motherboards support "soft jumper", that is, setting the external frequency of CPU through "BIOS", this kind of soft jumper can only set the non-standard external frequency of a certain section (for overclocking), for example, overclocking the new Cy Yang whose standard external frequency is 100MHz to 110MHz. If you want to overclock the new Cy Yang of 100MHz external frequency to a standard external frequency such as 133MHz, you often have to rely on jumpers. Note that the above is only used to briefly illustrate the function of "external frequency jumper". The most basic function of the jumper is to "correctly set the external frequency on the motherboard for different external frequency CPU, to make it work properly".


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