The relationship between CPU frequency and memory frequency

First make clear memory of three frequency, core frequency, operating frequency, equivalent frequency (also into interface frequency), usually said that the DDR2 800 of the 800 is the equivalent frequency of the memory (interface frequency), but also the most meaningful frequency, and memory bus bandwidth directly linked, such as DDR2 The 800 bandwidth algorithm is 800MHZX64/8, or 6.4gb/s. and the operating frequency is the equivalent frequency divided by 2, which applies to the DDRDDR2DDR3 (SD memory is invalid, but SD memory is obsolete, this is not studied here), because the English full name of the DDR is double data rate double, All DDR memory transmits data one at a time on the rising edge of the work cycle and on a falling edge, creating a double equivalent frequency for the operating frequency, which is used when overclocking the AMD K8 processor, and the memory frequency shown in the Cpu-z is also the operating frequency, so this frequency is more important in overclocking, The other core frequency is the most important, all the equivalent frequency is multiplied by the number of pre-fetching digits of the core frequency, since the DDR is a 2-bit prefetch, DDR2 is a 4-bit prefetch, DDR3 is a 8-bit prefetch, so the core frequency of the DDR is the equivalent frequency/2,DDR2 core frequency is the equivalent frequency/ The core frequency of the 4,DDR3 is the equivalent frequency/8.
After figuring out the three frequencies, start with an analysis, starting with AMD's K8 processor, give the formula: the real operating frequency of the memory in the computer =CPU the current operating frequency/crossover factor, wherein the frequency division coefficient algorithm is very special, is the CPU raw frequency/bios set memory operating frequency (focus on the operating frequency, If the BIOS is set to DDR2 800, it is necessary to use 400 generation into the calculation of the result into a get, into one is if the number is a decimal, then the number after the decimal point is removed, plus one, such as 4.8 into one is 5, 4.1 into a 5. Take AthlonX2 4200+ As an example, the CPU original frequency =200x11=2200mhz now inserted into a DDR2 800 and set to auto in the BIOS, the BIOS will automatically read the SPD information, set the equivalent frequency of 800MHz, Then the operating frequency is 400MHz according to the formula, the first calculation of the frequency division coefficient, the original clock/set of operating frequencies into one, that is 2200/400= 5.5, then use 5.5 into one equals 6, the division factor is 6, and then the current main frequency divided by the frequency factor, because there is no overclocking, so the last memory really work when the operating frequency =2200/6=366mhz, converted to equivalent frequency is 733mhz, that is DDR2 733, less than the 800 nominal frequency, which is also considered a common problem of this series of processors, the solution is only ultra-FSB. And because the memory of the operating frequency =CPU frequency/frequency factor, so in order to avoid overclocking CPU frequency limit, memory first die, the only way is to improve the frequency division factor, and the frequency division factor = Default CPU frequency/bios set in the memory to work in 13, So as long as the equivalent frequency of the memory in the BIOS set a little lower on the line, such as a DDR2 800, overclocking should be set to DDR2 667 in the BIOS to increase the overclocking success rate. And if think DDR2 800 of memory buy back can only work in DR2 733 too pity, can take to reduce octave, liters FSB method, in order to not super-frequency only super-FSB case to obtain higher memory equivalent frequency.
Next is AMD's K10 processor, this generation of processor computing method is much easier (is the other netizens experiment, and there is no official statement, can not guarantee that the algorithm is correct, wrong can not blame me OH), the true equivalent frequency of memory = current FSB/raw FSB * in the BIOS set memory equivalent frequency, Much like Intel's typical memory frequency algorithm. For example, the main frequency of the wing Dragon 2*4 955 is 200x16=3200mhz, then into a DDR3 1333 if not overclocking, in the BIOS memory equivalent frequency set to Auto or 1333, then the equivalent rate of memory is equal to 200/200x1333=1333mhz, Completely equal to the nominal frequency, remove the K8 when the criticism. If you exceed the frequency, 200 FSB to 240, then the equivalent frequency of memory is equal to 240/200.x1333=1599mhz, more simple than K8, but simplicity, the overclocking is still to pay attention to the frequency of memory to keep pace with FSB, if the wing Dragon 2x4 955 of 200 FSB to 250 FSB, plug in DDR3 1333, set to auto in the BIOS, then the conversion down the memory will work at 1666mhz High frequency, not all memory is up, so you can appropriately force the BIOS to reduce the memory equivalent frequency, For example, can be set to 1066, with 1066/200x250, the calculation is just 1333MHz, and this time the CPU has been sent to 4G high frequency.
Now switch to the Intel camp, the first discussion has FSB u, such as today's hot e5200,e7400, the previous hot E2140, is an algorithm, and the algorithm and AMD K10 algorithm is basically the same, the memory really works when the equivalent frequency =bios set the memory equivalent frequency x today FSB /original FSB, here is not cumbersome, and other motherboards directly provide division ratio, that is better to do, this crossover ratio is the FSB frequency: memory equivalent frequency, 1:1 is the most efficient, but with overclocking when the FSB more and more high, 1:1 of the memory may not be able to withstand, so you can choose some 5:4,4:3 such as the crossover ratio , in order to increase the overclocking success rate, the individual think the crossover ratio is more intuitive.
The final turn to the fastest CPU on the planet-------Core i7, this thing is too strong, but really, this CPU memory frequency and CPU frequency relationship is the most easily understood, i7 Hang like, have a FSB, but the official term is the basic frequency-----BCLK, Here and call him FSB. Currently i7 FSB unified 133MHz, basic all the main frequency, such as the clock, QPI bus frequency, memory frequency is from the FSB x a multiplier, so the memory frequency and FSB relationship is very intuitive, the equivalent frequency of memory = FSB * Memory multiplier, such as Core i7 920 memory multiplier is 8, Then in the BIOS in the memory multiplier can not be raised, the equivalent frequency of memory =133x8=1066, in other words, in the case of not overclocking, can only be memory work on 1066MHz, so if buy back DDR3 1333, but also to make him work in 1333, the only way is super FSB. In another case, overclocking requires a lot of high FSB, memory does not work at that high frequency, you can properly adjust the small memory multiplier, which need to be in overclocking as needed to operate.