Memory frequency

Computer terminology

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Memory main frequency and CPU main frequency Similarly, it is used to indicate the speed of the memory, which represents the maximum operating frequency that the memory can reach. The main frequency of memory is in MHz（ Megahertz ）It is measured in units. The higher the main frequency of the memory, to some extent, means the faster the memory can reach. The main frequency of the memory determines the highest frequency at which the memory can work normally.

Chinese name: Memory frequency
Foreign name: Memory frequency
Discipline: computer

Representative: Memory speed
Unit: MHz
Representation method: Operating frequency, equivalent frequency

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definition

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Memory frequency refers to Main frequency of memory , refers to the maximum operating frequency that the memory can reach. There are two representations, namely, operating frequency and equivalent frequency. The operating frequency is Memory granule Actual operating frequency, equivalent frequency is different, DDR memory The equivalent frequency is twice of the working frequency, and the equivalent frequency of DDR2 is four times of the working frequency. Because the rise and fall of the pulse in DDR memory transmit data, and each clock in DDR2 memory can run at a speed four times of the working frequency. Frequency can also be regarded as the transmission standard. The transmission standard is also a parameter of the memory speed. The transmission standard is the memory specification. If the memory adopts this transmission standard, it means that it completely conforms to the specification, so the transmission standard also represents the memory speed^[1] 。 For example, the working frequencies of DDR 200/266/333/400 are 100/133/166/200MHz respectively, while the equivalent frequencies are 200/266/333/400MHz respectively; The working frequencies of DDR2 400/533/667/800 are 100/133/166/200MHz respectively, while the equivalent frequencies are 400/533/667/800MHz respectively.

principle

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Computer system Clock speed It is measured by frequency. crystal oscillator It controls the clock speed, applies voltage to the quartz chip, and it vibrates in the form of sine wave. This vibration can be recorded by the deformation and size of the chip. The vibration of the crystal is shown in the form of sinusoidal harmonic changing current, which is clock signal 。 The memory itself does not have a crystal oscillator, so the clock signal when the memory is working is determined by Mainboard chipset North bridge of or directly from mainboard Clock generator Provided, that is, the memory cannot determine its own working frequency The actual operating frequency is determined by the motherboard.

significance

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Memory asynchronous working mode It has multiple meanings. In a broad sense, memory working frequency With CPU fsb When inconsistent, it can be called memory asynchronous working mode. First of all, the earliest memory asynchronous working mode appeared in the early motherboard chipset, which can make the memory work at a higher speed than CPU external frequency In the high 33MHz or low 33MHz mode (note that the difference is only 33MHz), the system memory performance can be improved or the old memory can continue to use its residual heat. Secondly, in the normal operating mode (CPU does not Overfrequency ）Many motherboard chipsets also support memory asynchronous working mode. For example, the Intel 910GL chipset only supports 533MHz FSB, that is, 133MHz CPU external frequency, but it can work with 133MHz DDR 266 The DDR 333 with a working frequency of 166MHz and the DDR 400 with a working frequency of 200MHz work normally (note that the CPU external frequency of 133MHz is 66MHz different from the working frequency of the DDR 400 with a working frequency of 200MHz), but the performance of the DDR 333 with different memories is different. Again, on CPU overclocking In order to prevent the memory from dragging down the CPU's overclocking capability, the memory working frequency To facilitate overclocking, for example, the Opteron 144 of AMD's Socket 939 interface is very easy to overclock fsb You can easily exceed 300MHz. If you work in the memory synchronization mode, the equivalent frequency of the memory will be up to DDR 600, which is obviously impossible. In order to successfully exceed 300MHz external frequency, we can set the memory to DDR 333 or DDR 266 in the motherboard BIOS before overclocking. After exceeding 300MHz external frequency, the former is only DDR 500 (some excellent memory can achieve this), In the latter case, there is only DDR 400 (completely a normal standard frequency). It can be seen that correctly setting the memory asynchronous mode is conducive to successful overclocking.

Memory speed

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Generally speaking, "fast" refers to the speed of accessing data when memory is working working frequency And data bandwidth. The memory frequency is directly linked to the memory data bandwidth. The conversion method is: frequency × 8=bandwidth. For Intel, external frequency × 4=front-end bus (FSB), and FSB × 8=CPU data bandwidth. Generally speaking, the CPU bandwidth should be equal to or less than the memory bandwidth in order to make full use of the CPU performance. For example, the external frequency of P4 is 200MHz, the FSB is 800MHz, the bandwidth is 6400MB/s, and the bandwidth of DDR400 is 3200MB/s; Because you can use Memory dual channel The data bandwidth is doubled, so the DDR400 can reach 6400M/s, which can meet the CPU bandwidth requirements. If CPU overclocking is taken into account, it is also necessary to consider buying more frequent memory. For example, the 1066MB front-end bus requires dual channels of DDR2533 memory groups. However, overclocking is usually considered, so DDR2667 or DDR800 is equipped. In addition, only Intel's CPU has this relationship. Because AMD has a built-in memory controller, the actual memory usage frequency is uniquely determined by dividing the main frequency of the CPU by the frequency division. The calculation is complex and needs to refer to more professional technical data. But the principle is the same: the CPU bandwidth should be equal to or less than the memory bandwidth.

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