Overclocking Core i7 920: CPU and DDR3 Memory Speeds & Multiplers

chriscooke · 25 Nov 2008 at 23:48

Hi there

I'm looking at getting a Core i7 920 with 6gb of PC3-12800 (1600mhz) DDR3 Memory and an Asus P6T Motherboard

I was thinking about overclocking the CPU to around 3.4-3.6ghz, as most people seem to say the i7 will run fairly stable at this speed and the PC will most likely be running 24/7

I was wondering what the options are as regards to getting the memory to run at 1600mhz... as I've heard the P6T only allows for a memory multipliier of 6 or 8 - meaning you would have to run the BCLK at 200mhz to achieve 1600mhz (200 x 8), which would make the CPU run at 4ghz! (200 x 20)

This is how I understand the multiplers for the memory & CPU to work with the BCLK as an example... please someone correct me if I am wrong here

Has anyone got examples of what speeds, multipliers & voltages you've got your i7's and memory runnning at and what memory & board you've gone for?

Thanks

zykan · 26 Nov 2008 at 00:44

there was an article about this posted a few days before i7 officially launched, they got 2.66 to 4.02 on air, and i can't remember the ram. Can't be that old, try searching for it! i7 benchmarks or something maybe? hf

steve258 · 26 Nov 2008 at 01:10

Is it not possible to reduce multiplier on core i7?

fornowagain · 26 Nov 2008 at 01:21

From what I gather these are the multi available on a Gigabyte UD5 with a retail 920. You only get the even multipliers as far as I know. 6, 8, 10 etc. I've seen a few P6T reporting x20 multi limits, they seem to prefer x19 for maximum clocks.

Core = x12 - x20
Uncore = x12 - x48
Mem = x6 - x18
QPI = x36 - x48

UD5+920

chriscooke · 26 Nov 2008 at 09:33

fornowagain said:
You only get the even multipliers as far as I know. 6, 8, 10 etc. I've seen a few P6T reporting x20 multi limits, they seem to prefer x19 for maximum clocks.

Does anyone know what the options are for the multiplier on an Asus P6T?

If the memory multiplier was 19 or 20 wouldn't you have to run the BCLK at around only 80mhz to acheive a memory speed of 1600mhz?? Which would cause your i7 920 to run at very slow speeds...! Or am I understanding this wrong?

fornowagain · 26 Nov 2008 at 09:45

chriscooke said:
Does anyone know what the options are for the multiplier on an Asus P6T?

If the memory multiplier was 19 or 20 wouldn't you have to run the BCLK at around only 80mhz to acheive a memory speed of 1600mhz?? Which would cause your i7 920 to run at very slow speeds...! Or am I understanding this wrong?

You'll find the multi available are even numbered, not sure which ones the P6T has. At least 6 and 8 for the memory.

The cpu multiplier on a 920 is a maximum of x20 (excluding turbo modes). Some owners have reported having issues with x20 not reaching as far as x19. Not sure if its board or chip specific, probably just down to immature bios'.

e.g. say using the x6 memory multi.

20 x 200 BCLK = 4000Mhz / 6 x 200 = 1200Mhz

19 x 215 BCLK = 4085Mhz / 6 x 215 = 1290Mhz

chriscooke · 26 Nov 2008 at 12:38

So if I want to run my CPU at 3.6ghz, I can run it like this: -

BCLK @ 180mhz x 20 = 3.6ghz CPU / 180mhz x 8 = 1440mhz Memory

but this way the memory would only run at 1440mhz - So if I wanted to run my memory at 1600mhz, could I lower the multipler on my CPU to 18 times with a the BCLK at 200mhz like this?

BCLK @ 200mhz x 18 = 3.6ghz CPU / 200mhz x 8 = 1600mhz Memory

With the BCLK running at a higher speed of 200mhz constantly, is this likely to generate more heat from the motherboard and potentially reduce it's overall lifespan?

fornowagain · 26 Nov 2008 at 14:57

chriscooke said:
So if I wanted to run my memory at 1600mhz, could I lower the multipler on my CPU to 18 times with a the BCLK at 200mhz like this?

BCLK @ 200mhz x 18 = 3.6ghz CPU / 200mhz x 8 = 1600mhz Memory

With the BCLK running at a higher speed of 200mhz constantly, is this likely to generate more heat from the motherboard and potentially reduce it's overall lifespan?

Correct.

More heat? Maybe a tiny bit. Its more about if 200 BCLK is stable and the voltages required. The thing to consider is that there are other clock domains based on the BCLK. The uncore and QPI also use the same clock generator and they have their own multipliers and maximum clocks.

Crashgate3 · 26 Nov 2008 at 15:00

I seem to remember reading that there was some difference between the retail 920s and the OEM ones with regards to overclocking. Is there any truth in that?

psychas · 26 Nov 2008 at 15:19

nice article would lke to see how 920 performs as they say they are restricted to overclock or that was rubish from intel as always?

fornowagain · 26 Nov 2008 at 16:44

Crashgate3 said:
I seem to remember reading that there was some difference between the retail 920s and the OEM ones with regards to overclocking. Is there any truth in that?

Doubt that tbh, there are differences between production and ES engineering samples. A lot of those get used for early reviews and the rumours start from there.

psychas said:
nice article would lke to see how 920 performs as they say they are restricted to overclock or that was rubish from intel as always?

Bit of both, the locked i7 do have power limits that can be used to throttle the chip, however these can be disabled with the latest bios/boards. So its a non issue.