clock frequency

Basic frequency of clock in synchronous circuit

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Clock frequency clock rate ）, refers to the basic frequency of the clock in the synchronous circuit, which is measured in "several cycles per second", and the measurement unit is SI Units hertz （Hz）。 It is an assessment CPU performance Important indicators. Generally speaking, the larger the digital value of the main frequency, the better. External frequency is the working frequency outside the CPU and the reference clock frequency provided by the motherboard. FSB frequency, connecting CPU and Mainboard chipset In Beiqiao chip Data on the Front Side Bus of Transmission frequency 。 There is such a relationship between the main frequency and the external frequency of the CPU: Dominant frequency = fsb × frequency doubling 。

Chinese name: clock frequency
Foreign name: clock rate
Alias: Clock frequency speed

Definition: Basic frequency of clock in synchronous circuit
Unit of measure: SI unit Hertz (Hz)
Indicators: Important indicators for evaluating CPU performance

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brief introduction

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clock frequency

In electronics, Pulse signal It is a pulse signal sent continuously at a certain voltage amplitude and time interval. Pulse signal The time interval between is called period; The number of pulses generated in a unit time (such as 1 second) is called frequency. Frequency is used to describe periodic cyclic signals (including Pulse signal ）Measurement name of the number of pulses in unit time; The standard unit of measurement for frequency is Hz. On the computer System clock Is a typical frequency that is quite accurate and stable Pulse signal generator 。 The frequency is represented by "f" in the mathematical expression, and its corresponding units are: Hz (Hz), kHz（ Kilohertz ）, MHz (megahertz), GHz [gigahertz (1 gigahertz=1000000000)].^[1]

Where 1GHz=1000MHz, 1MHz=1000kHz, 1kHz=1000Hz. The time unit for calculating the pulse signal period and the corresponding conversion relationship are: s (second), ms (millisecond), μ s (microsecond), ns (nanosecond), where 1s=1000ms, 1 ms=1000 μ s, 1 μ s=1000ns. Transcoding clock frequency As shown in Figure 1.

Figure 1 Clock Frequency of Transmission Code

CPU main frequency

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The main frequency of the CPU, that is, the clock speed of the CPU core (CPU Clock Speed). Generally speaking, the number of GHz of a certain CPU is "the dominant frequency of the CPU". Many people think that the main frequency of CPU is its running speed, but it is not. The main frequency of the CPU indicates the speed at which the digital pulse signal oscillates in the CPU, which has no direct relationship with the actual computing power of the CPU. Main frequency and actual Operation speed There is a certain relationship, but so far there is no definite formula that can quantify the numerical relationship between the two, because the CPU operation speed depends on the performance indicators of the CPU pipeline in all aspects（ cache 、 Instruction set , CPU bits, etc.). Since the main frequency does not directly represent the operation speed, under certain circumstances, it is likely that the CPU with higher main frequency will have a lower actual operation speed.

For example, most of AMD's AthlonXP series CPUs can achieve Intel The company's Pentium 4 series CPUs have higher performance than the main frequency CPUs, so the AthlonXP series CPUs are named by the PR value. Therefore, the dominant frequency is only one aspect of CPU performance, not the overall performance of the CPU. The main frequency of the CPU does not represent the speed of the CPU, but increasing the main frequency will improve the CPU Operation speed But it is very important. For example, suppose a CPU is in a Clock cycle If an operation instruction is executed within, the CPU will run twice as fast when it runs on the 100MHz main frequency as when it runs on the 50MHz main frequency. Because the 100 MHz clock cycle occupies half the time of the 50 MHz clock cycle, that is, the time required for a CPU working on the 100 MHz main frequency to execute an operation instruction is only 10 ns, which is half shorter than the 20 ns working on the 50 MHz main frequency, and the natural operation speed is twice as fast. But the overall running speed of the computer depends not only on the CPU operation speed, but also on the operation of other subsystems Data transmission speed The overall running speed of the computer can be really improved only after it has been improved.^[1]

Restrictions

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clock frequency

The improvement of CPU working frequency is mainly limited by the production process. Since CPU is manufactured on semiconductor silicon chip, wires are required to connect components on silicon chip. The thinner and shorter wires are required in high-frequency state, so as to reduce stray interference such as distributed capacitance of wires and ensure correct CPU operation. Therefore, the limitation of manufacturing process is CPU main frequency One of the biggest obstacles to development.^[2]

Development History

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clock frequency

The clock frequency is measured in "several cycles per second", using international standard units hertz （Hz）。 The computer performs its most basic actions, such as adding two numbers or transferring values from one register to another. Different chips in the same Computer motherboard There may be different clock frequencies. Usually when it comes to computers, the "clock frequency" is specified to use the speed of the CPU. The clock frequency of the CPU is usually determined by the frequency of the oscillator crystal. Original IBM personal computer In about 1981, there was a clock frequency of 4.77 MHz (4770000 cycles/second). In 1995, Intel Its Pentium chip runs at 100 MHz (100 million cycles/second). In 2002, Intel Pentium 4 The model was introduced as the first CPU with a clock frequency of 3 GHz (3 billion cycles/second).

Clock frequency is the only way to compare the performance of chips in the same family. An IBM PC running at 50 MHz with an Intel 486 CPU will be twice as fast as one running at 25 MHz with the same CPU, memory and display. However, there are many other factors to consider when comparing the speed of the whole computer, such as the clock of the front bus of the computer frequency ， Memory chip Clock frequency, width in CPU's bus bits, and a considerable number of level 1 and level 2 high-speed cache 。

The clock frequency should not be used when comparing different computers or different processor families. Instead, a software benchmark should be used. The clock frequency may be very misleading, because different computer chips may make a considerable number of work changes in a cycle. For example, RISC CPUs tend to have simpler indication CPUs (but higher clock frequency) than CISC CPUs, and processors transported by pipeline execute more than one indication per cycle.

In the early 1990s, most computer companies first advertised the speed of their computers by mentioning their CPUs' clock frequency. This has led to various marketing competitions, such as the decision of Apple Computer to create and sell the Macintosh 8100/110 at a clock frequency of 110 MHz, so that Apple Computer can advertise that its computer has the fastest clock speed available -- the fastest Intel processor Available when running at 100 MHz. This advantage lies in clock speed, however, it is meaningless; PowerPC and Pentium CPU buildings are completely different. PowerPC is faster in some tasks, but slower in others.

In 2000s, Intel's competitor AMD began to use model number instead of clock frequency to sell its CPUs, saying that the "megahertz myth" did not explain the power of its CPUs. In the middle of 2004, Intel announced that it would do the same, probably due to consumer confusion in its Pentium M mobile CPU, which reportedly ran at about half of the roughly equivalent Pentium 4 The clock frequency of the CPU.

Frequency and speed

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Relation between frequency and speed: Generally speaking, a Clock cycle The number of instructions completed is fixed, so the higher the main frequency, the faster the CPU speed. However, due to the different internal structures of various CPUs, the main frequency cannot be used to summarize the CPU performance. but CPU main frequency The level of the computer can determine the level and price level of the computer. Take the Pentium 4 2.0 as an example. Its operating frequency is 2.0GHz. What does this mean?

Specifically, 2.0 GHz means that it will generate 2 billion Clock pulse Signal, each clock signal The period is 0.5 nanoseconds. The Pentium 4 CPU has four pipeline computing units. If the load is uniform, the CPU can perform four binary addition operations in one clock cycle.

This means that the Pentium 4 CPU can perform 8 billion binary addition operations every second. But so amazing Operation speed Can't completely serve users, Computer hardware And the operating system itself also consumes CPU resources. But Athlon XP processor PR nominal mode is adopted, and 266MHz disclosed by AMD Front end bus frequency Athlon XP processor for Nominal frequency The conversion formula between Athlon XP 2100+and actual frequency 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 2100+is 1733MHz=2 × 2100/3+333

Concept interpretation

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Overall structure of frequency synthesizer

A beautiful music will have a theme, and the theme of the computer is the CPU clock frequency. Dominant frequency fsb and frequency doubling Where did they come from? Frequency locking 、 Overfrequency What's going on?

There are many semiconductor chips in computers chip They work at a specific clock frequency. Clock generator Provided to the chip clock signal It is a continuous pulse signal, and the pulse is equivalent to the pulse of the chip. Each time the pulse arrives, the transistor in the chip will change its state once, allowing the entire chip to complete a certain task.

The vast majority of chips in computers belong to digital logic chips. Many transistors in digital chips are all working in the switch state, and their on and off actions are all in accordance with the rhythm of the clock signal. If the clock frequency is too high, the state of the transistor may not change in time, resulting in deadlock or random misoperation. Therefore, each chip has its own frequency limit.

What is the frequency

The frequency is expressed in f, and the basic unit is "once per second", which is recorded as Hz. 1Hz is once per second, and 10Hz is 10 times per second. However, the unit Hz is too small in computers, so it is usually expressed in KHz, MHz or GHz signal frequency 。 With the increase of frequency, THz will be used as the unit of frequency in a few years (Table 1).

Table 1: Frequency representation
Frequency unit	kHz	MHz	GHz	THz
Conversion relationship	1×10^3Hz	1×10^6Hz	1×10^9Hz	1×10^12Hz
English name	Kilo Hz	Mega Hz	Giga Hz	Tera Hz
Chinese name	Kilohertz	Megahertz	gigahertz	Terahertz

1. Period and frequency

In computer technology, a common term corresponding to frequency is cycle. The period is the reciprocal of the frequency. The higher the frequency, the shorter the period. For example, when the clock frequency is 1GHz Clock cycle Is 1 nanosecond.

two bandwidth And frequency

Another parameter related to frequency is Data transmission rate , also called "bandwidth", is used to measure the speed of data communication. In general, bandwidth=clock frequency ×（ Bit width ÷8)。 for example PCI bus The clock frequency of is 33.33MHz. Because its bit width is 32bit, its bandwidth is 33.33 × (32 ÷ 8)=133MB/s.

three Frequency of CPU : In 286 and earlier computers, the CPU frequency is the same as External bus Has the same frequency. Intel 386 computers use clock division, Clock circuit Provided to CPU clock signal The frequency of the CPU is 33MHz, while the internal CPU operates at 66MHz. Intel 80486 DX2 uses frequency doubling Mode, which allows the CPU to run at the speed of 2 or 3 times that of the external bus, but still communicate with the outside world at the original clock frequency. After entering the Pentium era, Frequency doubling technique Widely used, processor The frequency multiplication of has reached 20 times.

System clock frequency : Also known as“ fsb ”-- Clock frequency of CPU external bus. External frequency is determined by frequency synthesizer The chip is provided, and the frequency synthesizer chip will be introduced in detail later. Main frequency: the main frequency is the CPU core (integer and Floating point arithmetic unit ）The actual operating frequency of the circuit is determined by the external frequency (or Front end bus frequency ）It is determined jointly with the magnification, that is, the dominant frequency=external frequency × magnification.

Front end bus frequency : Front Side Bus (FSB) frequency is the frequency of data exchange between CPU and Beiqiao chip fsb There are both connections and differences. External frequency is the front-end bus clock signal The front-end bus frequency refers to the frequency of data transmission. For Pentium 4 processor For example, due to the adoption of QDR (Quad Data Rate) technology, 1 Clock cycle The data can be transmitted four times within, so the front-end bus frequency is four times of the external frequency: the FSB 800MHz processor, the external frequency is only 200MHz.

Who is generating frequency

We can use clock signal The generator is regarded as the heart of the computer. Only when the heart beats can the computer work.

1. Oscillation source: crystal oscillator

The chip itself usually does not have a clock signal source, so a special Clock circuit Provide clock signal, Quartz crystal oscillator (Quartz Crystal OSC) is one of the most commonly used clock signal oscillators.

quartz crystal Is pure silicon dioxide Is a single crystal of silicon dioxide, which is often referred to as crystal. There are two kinds of quartz crystal: natural (Crude) crystal and synthetic (synthetic) crystal. The impurity content and morphology of natural quartz crystal are not uniform, so the crystal oscillator in electronic circuit mostly uses artificial quartz crystal.

Quartz is formed by cutting a wafer (called "wafer") from a crystal at a certain azimuth angle, coating a thin layer of silver on two surfaces of the wafer, connecting a pair of metal plates, welding pins, and packaging with a metal shell crystal oscillator 。

The quartz chip can be used as an oscillator because of its piezoelectric effect: adding an electric field to the two poles of the chip will cause mechanical deformation of the crystal; When an alternating voltage is applied to the quartz chip, the crystal will produce mechanical vibration, and the mechanical deformation vibration will also produce an alternating electric field. Although the voltage of this alternating electric field is extremely weak, its vibration frequency is very stable. When the frequency of the applied alternating voltage is equal to the natural frequency of the chip (determined by the size and shape of the chip), the amplitude of mechanical vibration will increase sharply, which is called "piezoelectric resonance".

The establishment and maintenance of piezoelectric resonance state must be realized by means of oscillator circuit. A series oscillator, a two-stage amplifier composed of transistors T1 and T2, and a LC circuit composed of quartz crystal XT and capacitor C2. In this circuit, quartz crystal is equivalent to an inductance, and C2 is Variable capacitor The circuit can enter resonance state by adjusting its capacity. The power supply voltage of the oscillator is 5V, and the output waveform is square wave.

quartz crystal oscillator Of Frequency stability Up to 10 ^ - 9/day, or even 10 ^ - 11. For example, for 10MHz oscillator, the frequency change within one day is generally not greater than 0.1Hz. Therefore, crystal oscillator can be regarded as a constant reference frequency source (quartz crystal is used as the reference frequency for timing in quartz watches and electronic watches). Since the birth of PC, a 14.318MHz quartz crystal oscillator has been used as the reference frequency source on the motherboard. As for the reason why the 14.318MHz frequency is always used, it may be the need to maintain compatibility. However, the author also found the 14.318MHz crystal oscillator in the video card, flash drive and mobile phone, so I don't know why.

In addition to this 14.318MHz crystal oscillator, there is also a 32.768KHz crystal oscillator on the motherboard, which is used for Real time clock (RTC) circuit, which displays accurate time and date.

2. Frequency divider and frequency multiplier

The function of frequency divider is to reduce the pulse frequency by n times. In the first generation PC, quartz crystal oscillator The output frequency is 14.318MHz, while Intel 8086 processor The dominant frequency of is 4.77MHz, and the latter is just 1/3 of the former. The work of frequency conversion is based on Intel 8284 (clock generator/ Driver ）Because the Intel 8284 chip is integrated with a three frequency division circuit, it can reduce the pulse signal generated by the crystal oscillator by three times and provide it to the CPU and peripherals

As the main frequency of the CPU increases, the crystal oscillator needs to be increased several times to meet the needs of the CPU Clock circuit The middle frequency multiplier replaces the divider. If the frequency divider performs division, the frequency multiplier performs multiplication, which increases the frequency of the crystal oscillator by n times.

Clock chip: programmable frequency synthesizer

Integrated Clock circuit , is a sign of hardware technology progress. Different devices in the computer have different requirements for the clock frequency. If you find a 286 motherboard from the waste box, you can see that several crystal oscillators are arranged together. CPU in the computer, AGP slot 、 PCI slot 、 Hard disk interface , USB port and PS/2 port are very different in communication speed, so different clock frequencies need to be provided, for example, PCI requires 33MHz, USB requires 48MHz, etc. However, a quartz oscillator can only provide one frequency, so motherboard manufacturers usually integrate these oscillatory circuits originally scattered everywhere on the motherboard into a "Frequency Synthesizer" chip crystal oscillator Frequency division (or frequency doubling ）To provide the required clock frequency for chips (or devices) with different operating speeds.

The common frequency divider is an integer frequency divider, and the relationship between its output frequency and input frequency is an integer multiple. It can only adjust the frequency piecewise, which cannot meet the requirements of precision adjustment. The frequency synthesizer is a "fractional frequency divider", which can fine adjust the output frequency. R&D engineers can freely design various frequencies in the circuit, and are no longer limited to the fixed frequency specifications of quartz oscillatory crystals. On the computer Clock chip Generally, it has the ability of "fractional frequency division", and the adjustment step size can be designed to 1% or even 0.1% as required. In order to guide and standardize the design and application of frequency synthesizers, Intel has developed a frequency synthesizer design guide, such as CK97, CK40X, etc., which is applicable to the latest Pentium 4 processor The specification of is CK410.

1. Frequency regulation principle

The frequency synthesizer is a frequency negative feedback clock signal In the system, two frequency dividers are used, Mdiv is used to reduce the reference frequency, and Ndiv is used to divide the VCO. crystal oscillator The frequency fi generated by (OSC) gets the reference frequency fref after passing through the M-frequency divider. It and the feedback frequency ffd are respectively sent to the two reverse inputs of the frequency detector (FD). The discriminator outputs a DC voltage that reflects the quotient of the two. After the AC component is filtered by the low pass filter (LPF), it is supplied to the voltage controlled oscillator, VCO) output frequency signal fout.

The relationship between the output frequency fout and the input frequency fin of the frequency synthesizer can be expressed by the formula fout=fin × (N+k/M), where N, M and K are integers, and K can be any integer between 0 and M. Non integer value N+k/M is usually written as N F， The dot here represents the decimal point, N represents the integer part of the frequency, and F=k/M represents the decimal part of the frequency. Under the condition that the input frequencies fin, N and M do not change, the required frequency value fout can be obtained by modifying the value of k.

In the frequency synthesizer chip, there is a special SMBus interface circuit, which is register It is a way to communicate with the outside world. With it, registers can be rewritten through BIOS or software. There are two possibilities for each bit of data in the frequency register, "0" or "1". When these bits are combined according to different states, a variety of data can be obtained fsb Output.

The frequency adjustment accuracy of the frequency synthesizer is related to the number of bits of the frequency register. For example, if the frequency register is 5 bits, the adjustment step is 1MHz. The more the number, the higher the adjustment accuracy. In the practical frequency synthesizer, both Mdiv and Ndiv frequency dividers are programmable. As long as the user sets the corresponding foot value, the BIOS can automatically give the N, M and K values, and write them into the corresponding register through the SMBus bus.

2. Automatic control principle of PLL for phase synchronization

Clock chip It is the heart of the computer, and its performance and stability directly determine the whole hardware system Performance. On the one hand, the frequency synthesizer can save cost and motherboard space, and the more important purpose is to make the motherboard chips and peripheral Of clock signal Keep strict synchronization relationship with CPU clock signals to ensure correct data exchange. FS chip not only has frequency doubling /The main feature of the frequency division function is the phase locking function - the phase of the output signal is forced to keep consistent with the phase of the reference signal. Therefore, although the frequency of various clock signals output by the frequency synthesizer is different, they are completely consistent in phase, and they all keep phase synchronization with the reference signal source.

In order to achieve phase locking, the clock signal output by VCO is compared with the reference frequency signal in the phase detector. If the two phases are different, an error voltage proportional to the phase difference will be output; The polarity of the error voltage determines whether the current source in the charge pump absorbs or sends current, so the charge will flow into or out of the capacitor in the filter. The amount of charge flow is proportional to the size of the phase difference. Voltage controlled oscillator It is a voltage controlled oscillator, internal Varactor diode When the voltage at both ends changes, its capacitance will change accordingly, thus changing the frequency of the oscillator.

The voltage controlled oscillator is the core unit of the PLL circuit. The phase control process is realized by changing the input voltage (i.e. tuning voltage) of the voltage controlled oscillator. The size and polarity of the tuning voltage determine whether the phase adjustment is lagging or leading, so that the phase error can be corrected.

3. Other functions of frequency synthesizer

Using frequency synthesizer chip in motherboard design can easily realize clock frequency adjustment and phase locking. In addition to these functions, the frequency synthesizer also allows mainboard design engineers to keep the components of various related interfaces synchronized by fine-tuning the clock delay between various interface clocks, which facilitates design and debugging.

In addition, the frequency synthesizer chip can also make a difference in system stability and security. On the one hand, the frequency that does not need to be adjusted can be locked to prevent CPU Overfrequency The failure of other equipment; On the other hand, some frequency synthesizer chips are also designed“ watchdog ”Function, once overclocking fails crash This function can register Clear to make the system start normally according to the default frequency of the CPU.

Nowadays, the application of frequency synthesizer chips is very common, such as ICS, Cypress, IDT, Realtek and Winbond. However, in the nForce2 motherboard, the frequency synthesizer can no longer be found, because the frequency synthesis function has been integrated into the IGP/SPP chip.

AMD Athlon Series processor Of frequency doubling Signal workflow. When the RESET # signal arrives, the processor sends the FID signal to the logic signal conversion chip, which generates SIP (Serialization Initialization Packet) system bus Initialize and set.

Some connection lines called Golden Bridge are set on the CPU. The level of FID signal can be set by changing the on-off of Golden Bridge. The level of Golden Bridge is low when it is turned on and high when it is turned off. The FID signal is generated in the built-in frequency multiplication control unit, amplified by the built-in FID drive circuit, sent from the FID pin to the logic signal conversion chip, and the generated SIP data packet is returned from the BP_FID pin to the CPU. In this way, the frequency synthesis circuit inside the CPU can frequency doubling And fsb The two signals combine to synthesize the core frequency of the CPU.

three Memory frequency Settings for

The memory bus clock signal on the early motherboard was also generated by the frequency synthesizer. However, the newer motherboards have put aside the frequency synthesizer chip on the motherboard and Beiqiao chip Complete the setting of the clock frequency of the memory bus, which is called "memory asynchronous" in the industry.

Similar to the principle of automatic setting of CPU frequency, the frequency synthesizer in the Beiqiao chip also realizes automatic setting of frequency through certain means. The memory frequency is determined by the SPD (Serial Presence Detect) memory sequence on the memory module Memory chip ）Yes. SPD is similar to the BIOS on the motherboard and stores Memory chip Memory capacity working frequency , delay time (CAS, tRCD, tRP, tCA), working voltage, manufacturer information, etc. The Beiqiao chip reads the parameters in the SPD of each DIMM through the SDA pin of the SMBus bus, and the information of the SPD chip will be recorded in the register of the PLL circuit in the Beiqiao chip.

Memory bus clock and System clock The frequency of is often different. For example, when the system clock is 133MHz and the memory clock is 200MHz, there is a 67MHz difference between the two. This difference in frequency is called "memory asynchrony". However, in order to implement the Synchronous communication The two buses still need to be synchronized in phase. It is not technically difficult to achieve phase synchronization, as long as the PLL circuit in the North Bridge chip and the PLL circuit in the frequency synthesizer use the same reference frequency fref.

In fact, the frequency setting of plug and play external devices is the same as Memory frequency The automatic setting principle of is basically the same. The host reads the characteristic parameters including frequency in the ROM chip of the device, and then automatically allocates system resources and automatically configures drivers, so that the device can work normally.

Feel the pulse for the computer

1. Check the actual frequency and release the potential of the equipment

Intel Processor Frequency ID Utility is the CPU detection software released by Intel Corporation. The software lists two data items: "report frequency" and "expected frequency". The former item represents the current operating speed of the tested CPU, and the latter item represents the maximum operating speed designed by the tested CPU when it leaves the factory. If both data are consistent, it means that the CPU is not Overfrequency 。 If the reporting frequency is lower than expected, indicate processor I didn't give full play to my ability.

Using test software can roughly understand the working status of each device, which is very important for optimizing system performance. Similar to the above testing software, there are many more. All the frequencies to be tested can be displayed through the testing software. However, some advanced players doubt whether the frequency measured by the software is accurate. This suspicion is not groundless, because the platform on which the detection software runs is based on the reference frequency fref. If the reference frequency itself is not accurate, the frequency value measured by the software is difficult to guarantee. However, it is necessary to measure accurately clock signal The oscilloscope can be used.

peripheral Performance and interface circuit of working frequency There is a close relationship between them. Take the hard disk as an example. If software such as AIDA32 is used to measure the highest UDMA transmission mode of the hard disk, it is UDMA 6 (ATA-133), but the current UDMA transmission mode is UDMA 1 (ATA-33). That is, the hard disk could work at 133MHz, but the interface only exchanges data at 33MHz. Then the hard disk performance will be greatly reduced. In this case, it indicates that the potential of the device has not been realized. You should check whether the interface mode selection in the BIOS is correct or install the relevant IDE driver to solve the problem.

2. Prevent tachycardia

Low frequency will lead to low performance of the equipment. On the contrary, if the frequency is too high, it will lead to unstable operation of the equipment, or even a complete strike. Usually we are right Display chip And video memory Overfrequency After that, the display screen is a typical case. because Tachycardia When the equipment fails to work Computer failure Accounting for a considerable proportion of. For various reasons, some equipment working frequency Actually, I can't Nominal frequency Of. For the treatment of such problems, the author has introduced in detail in the article "Computer Fault Frequency Reduction Diagnosis Method" (Microcomputer, 2003, Issue 17). It is necessary to add here that if CPU overclocking After failing to start, discharge the CMOS, and the BIOS will fsb It will not cause serious consequences if the security mode of is started.^[3]

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