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cpu oc affects ram?

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  • Overclocking
  • RAM
  • CPUs
Last response: in Overclocking
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August 20, 2013 4:03:22 PM

Hallo there
I need to know-
I purchuased g.skill tridentz series 16gb ram kit that runs at 2133mhz on my new gaming rig. I am using h100i corsair hydro cooling series to oc my core i7 3770k up to 4.7 if possible or at least 4.5ghz. The oc will be done directly in the bios by increasing the multyplier. On this way where i do not chanhe the fsb value do i have to underclock my ram frequency in order to achieve a high cpu oc? Or the multyplier increase wont affect my ram frequencies?

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August 20, 2013 4:21:30 PM

matsamas said:
Hallo there
I need to know-
I purchuased g.skill tridentz series 16gb ram kit that runs at 2133mhz on my new gaming rig. I am using h100i corsair hydro cooling series to oc my core i7 3770k up to 4.7 if possible or at least 4.5ghz. The oc will be done directly in the bios by increasing the multyplier. On this way where i do not chanhe the fsb value do i have to underclock my ram frequency in order to achieve a high cpu oc? Or the multyplier increase wont affect my ram frequencies?


On older FSB driven systems the CPU clock and DRAM clock were both derived from a PLL driven by a common system clock. Overclocking the CPU could be done by either increasing the CPU clock multiplier, or increasing the frequency of the system bus. Absent an unlocked clock multiplier, the only way to overclock the CPU was to either overclock the DRAM as well, or reduce the DRAM clock ratio which could reduce memory bandwidth. High performance memory allowed DRAM to be clocked at significantly higher speeds without screwing around with the DRAM clock ratio.

On newer systems there's significantly more flexibility in the generation of the CPU and DRAM clocks. The principle is the same (they are both derived from the base clock). Whereas the FSB on older systems could easily be overclocked 80%-100%, the base clock on modern systems won't budge more than a few percentage points. To accommodate for this, Intel greatly increased the granularity of the CPU and DRAM clock multipliers.

On k series CPUs, the clock multiplier is unlocked, so you can boost it as high as it will go without affecting the DRAM multiplier at all. The opposite is also true in that each system supports a wide range of DRAM IO frequencies independent of the CPU's frequency.

Example #1, consider an old LGA775 platform with a Q6600 and DDR2-800,

Default FSB = 266Mhz

Q6600 clock multiplier = 9 (valid values are 6,7,8,9)

Q6600 clock frequency = 266Mhz * 9 = 2394Mhz (marketed as 2.4Ghz)

DDR2-800 IO bus frequency = 400Mhz

DDR2-800 clock ratio = 400/266 = 1.5 = 3:2 (valid values are usually 1:1,3:2,5:4,8:5)

Example #2, an LGA1155 platform with a 3770k and DDR3-2133

Default Base Clock = 100Mhz

3770k default multiplier = 35 (valid values are 16 through 57 inclusive I believe)

DDR3-2133 IO bus frequency = 1066Mhz

DDR3-2133 clock ratio = 1066/100 = 10.66 (valid values are 4 through 16 in one third steps I believe)

There's a lot more combinations which makes running arbitrary combinations of CPUs and memory possible. However, if the CPU is a non-k or non-x model, then it will have a locked CPU multiplier. In the event of a locked multiplier, the only way to overclock is the good old fashioned method of increasing the system base clock, which won't be more than a few percentage points.
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