"Frequency" is a common technical parameter, which will be used in many places, especially in the introduction of hardware. Frequency is an important index to measure the running speed of the system. High frequency means that the system runs fast, but different devices have different frequencies. Please see the following text introduction.
There is a rectangular crystal oscillator wrapped in metal on the motherboard. When the motherboard is powered on, it will vibrate electromagnetically, generating high-frequency electronic pulse signals. But these pulses are not accurate enough to match the frequency required by the computer, so it is necessary to input these original frequencies into the clock frequency generator chip near the crystal oscillator, shape and divide the original frequencies, and then turn them into various bus working frequencies when the computer needs them. The bus in the computer adopts hierarchical structure, and the running frequency is reduced step by step. The first stage is the data transmission channel between CPU and Northbridge chip, that is, the system front-end bus frequency; The second stage is the data transmission channel between the memory and the Northbridge chip, that is, the memory bus frequency; The third stage is the data transmission channel between AGP graphics card and Northbridge chip, which is the AGP bus frequency; The fourth level is the data transmission channel between PCI, ISA device and Southbridge chip, that is, PCI bus frequency.
The main frequency of CPU is also the clock frequency of CPU, which is simply the working frequency of CPU. Expressed by the formula: main frequency = external frequency × frequency doubling. Where the external frequency is the bus clock frequency; Frequency doubling refers to the multiple of the difference between CPU external frequency and main frequency.
Generally speaking, the number of instructions that are always completed periodically is fixed, so the higher the main frequency, the faster the CPU will be. However, due to the different internal structures of various CPUs, the performance of CPU can not be completely summarized by the main frequency. But the main frequency of CPU can determine the grade and price level of computer.
Take Pentium 4 2.0 as an example, its main frequency is 2.0GHz, which shows that it will generate 2 billion clock pulses per second, and each clock signal period is 0.5ns. Pentium 4 CPU has four pipeline operation units, and if the load is even, the CPU can perform four binary addition operations in 1 clock cycle. This means that Pentium 4 CPU can perform 8 billion binary addition operations per second. However, such an amazing budget speed can not fully serve users, and computer hardware and operating system itself will consume CPU resources. Q#xtd_
However, AMD's Athlon XP processor uses PR nominal mode. The conversion formula between the nominal frequency and the actual frequency of Athlon XP processor with 266MHz front-end bus frequency disclosed by AMD is as follows:
Nominal frequency =3× actual frequency /2-500/
Actual frequency =2× nominal frequency /3+333H 1.
For example, the actual frequency of Athlon XP 2 100+ is1733 MHz = 2× 2100/3+333.
Front-end bus (FSB) is the line connecting CPU and Northbridge chip. Before Pentium 4, the system front-end bus frequency was the same as the CPU external frequency. It is different for Pentium 4 and Athlon processors.
Pentium 4 processor adopts quadruple data transmission mode technology similar to AGP 4× working principle. For example, the external frequency of Pentium 4 at 3.06 GHz is 133MHz, so its front-end bus frequency is 533MHz= 133×4 (Note: there are some fixed standard data in hardware, especially in terms of frequency and capacity, which are sometimes not so accurate, such as133× 4 here. That's the reason. In fact, the frequency itself is not particularly accurate. For example, when Pentium 4 2.4BGHz processor is used under normal conditions, it will be found that its actual working frequency is not 2.40GHz, but 2.4 1GHz. This is because its external frequency has reached 133.95MHz, so the frequency like 533 actually represents a standard, or a grade, which is used to distinguish it from other standards or grades, and does not completely have the meaning of its number itself. Don't be surprised. ).
Similarly, AMD Athlon (called Athlon in Chinese), Athlon XP and Duron (called Duron in Chinese) series processors all adopt a technology that can transmit data on both the upper and lower edges of pulse signals, which AMD calls "double front-end bus". For example, AMD Athlon 900 uses 100MHz external frequency, but its front-end bus is 200MHz.
At present, the main memory types used are PC 133 SDRAM, DDR266/333/400 DDR SDRAM (also known as PC2400/2700/3200 DDR SDRAM) and PC800 RDRAM. I should pay attention to the difference between the memory clock frequency and the memory bus frequency. Memory clock frequency is very important to the performance of the whole system. Memory clock frequency refers to the frequency when the memory works, which is generally equivalent to the bus clock frequency. Memory bus frequency refers to the frequency of data transmission in memory.
For example, the memory clock frequency of PC 133 SDRAM is 133MHz, which can only transmit data on the rising edge of clock pulse, that is to say, only 1 data can be transmitted in one clock cycle, and the data access period is about 7ns, so the memory bus frequency of PC 133 SDRAM is also133 MHz. DDR SDRAM memory can transmit data at both rising and falling edges of clock pulse, so DDR SDRAM can transmit two data in one clock cycle. When the memory clock frequency is 133MHz, the memory bus frequency is 266MHz, and the data access period is about 3 ns. The memory clock frequency of PC800 RDRAM is 400MHz, and both the rising edge and the falling edge of the clock can be used to transmit data. If a dual-channel memory bus is used, the memory bus frequency will reach 800MHz. (Off-topic, the labels of DDR SDRAM are a little messy than others, including DDR400 and PC3200. Actually, they are the same. The difference is that the former uses the memory bus frequency when labeling, and the latter uses the memory bus bandwidth when labeling, that is, the bandwidth of DDR400 memory is 3200MB/s, while PC 133 and PC88.
AGP (Accelerated Graphics Port) interface is a new type of bus, which is specially used for high-speed connection between processor and graphics card. Just as the popularity of graphical interface operating system leads to the bandwidth bottleneck of ISA graphics card, when some applications that require high display performance based on 3D graphics become a trend, the bandwidth of PCI graphics card inevitably begins to be stretched. Here we also introduce the difference between AGP clock frequency and AGP bus frequency.
The bit width of AGP is 32 bits like PCI, but the clock frequency of AGP is twice that of PCI (66MHz). It is realized by the frequency division technology of the motherboard. From this we can also know that the AGP clock frequency is not fixed, but depends on the bus clock frequency, that is, the external frequency of CPU. When the bus clock frequency is 66MHz, 100MHz and 133MHz, the motherboard will keep the AGP clock frequency at 66MHz by frequency division technology, and when the external frequency increases to non-standard frequency, such as 125MHz, the AGP clock frequency will work at 83.3MHz.
The frequency of AGP bus is also based on the clock frequency of AGP, which changes with different AGP specifications. Under AGP 1×, the frequency of AGP bus and AGP clock is 66MHz；; AGP 2× adopts the frequency doubling transmission technology similar to DDR, so the bus frequency of AGP 2× reaches 133MHz, while the clock frequency of AGP2× is still 66MHz. AGP 4× adopts QDR(Quad Data Rate) quadruple transmission technology, so the bus frequency of AGP 4× reaches 266MHz, while the AGP clock frequency is still 66MHz. AGP8X is an octave transmission technology using ODR(Octal Data Rate), so the bus frequency of AGP8X reaches 533MHz, while the clock frequency of AGP is still 66MHz. It can be seen that the standard of AGP clock frequency has not changed, which is 66MHz, and it is said that the standard of the next generation AGP will change the AGP clock frequency.
PCI sound card, PCI network card, IDE hard disk and IDE CD-ROM all work under PCI bus. The PCI bus frequency and PCI clock frequency are both 33MHz, which are also realized by the frequency division technology of the motherboard. When the bus frequency is 66MHz, 100MHz, and 133MHz, the motherboard will keep the PCI bus working at 33MHz through frequency division technology. When the external frequency is raised to a non-standard frequency, such as 125MHz, the PCI bus will work at 4 1.6MHz, so many components will work. At this time, whether the hard disk can hold up is the most important, because after the PCI bus frequency is increased, the data exchange speed between the hard disk and the CPU is accelerated, which is likely to lead to abnormal reading and writing, thus causing a crash. On the other hand, if all devices are ok, then higher PCI bus frequency can obviously improve the running speed of the system.