Who provides the clock frequency for the computer? There is a rectangular crystal oscillator wrapped in metal on the motherboard (as shown in figure 1). When the motherboard is electrified, it will vibrate electromagnetically, producing a series of high-frequency electronic pulse waves. 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. Bus is the channel for data transmission inside the computer. The bus is made on the motherboard and consists of many wires. The computer bus adopts hierarchical structure, and the running frequency is gradually reduced. 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.

Second, the CPU 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 completed in a clock cycle is fixed, so the higher the main frequency, the faster the CPU. 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. What does this mean? Specifically, 2.0GHz means that 2 billion clock pulses are generated every second, and the period of each clock signal is 0.5 nanosecond. Pentium 4 CPU has four pipeline operation units. 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 amazing computing speed can not fully serve users, and computer hardware and operating system itself will consume CPU resources.

However, Athlon XP processor adopts PR nominal mode. The conversion calculation formula between the nominal frequency and the actual frequency of Athlon XP processor with front-end bus frequency of 266MHz disclosed by AMD is as follows:

Nominal frequency =3× actual frequency /2-500

Actual frequency =2× nominal frequency /3+333

For example, the actual frequency of Athlon XP 2 100+ is1733 MHz = 2× 2100/3+333.