Sign in with
Sign up | Sign in
Your question
Solved

Problem with core i5 750 and DDR3 1600 XMP

Last response: in CPUs
Share
January 31, 2010 3:09:46 AM

I just bought an Asus P7P55-M mobo, a core i5-750 cpu and 4GB OCZ DDR3-1600 XMP edition (which is 100 after rebate). When I read the mobo's manual, it's said "according to intel cpu spec, CPUs with a core frequency of 2.66G support the maximum DIMM frequency of up to DDR3-1333 (I didnt know about that). To use DIMMs of a higher frequency with a 2.66G, enable the DRAM O.C Profile feature in the BIOS. However, in the Ai tweaker menu section of the manual, it's also said "if you install memory modules supporting the XMP technology, choose XMP mode (in the Ai Tweaker menu) to set the profile supported by your memory modules for optimizing the system performance". I am now confused. Can anyone tell me what I should do ?
a b à CPUs
January 31, 2010 3:51:52 AM

Start machine. Hit delete key until you get into the bios. Once there look for I.A. Tweaker..... set as per instruction...XMP........ hit f10 and enter.. ( should have saved......or do as instructed at bottom of screen to save it ).......... let machine reboot. It should now read the memory correctly... ie 1600 without having to do anything extra if you're lucky.
m
0
l
a b à CPUs
January 31, 2010 3:54:59 AM

You can also try READING the book that came with the motherboard...... CMON TOMS....FIX THE NOT ALLOWED TO MAKE CHANGES THING HUH ?
m
0
l
Related resources
January 31, 2010 4:16:43 AM

thanks ! it seemingly works.
m
0
l

Best solution

a b à CPUs
February 1, 2010 12:38:11 AM

With the P55 motherboards the CPU determines what memory speeds (via the memory multiplier) are allowed.

With an i5 750 you cannot run RAM any faster than 1333 with effectively OCing your computer or making trade-offs. You can often turn on XMP in BIOS, but this changes your BCLK which also affects your CPU speed. It will likely, as a side effect, end up turning off functionality such as Turbo, EIST, sleep states. You can usually turn most of those back on but you have to specifically do it. But Turbo will be lost unless you OC your CPU. This differs from motherboard to motherboard.

To provide a little more detail on why memory multipliers and XMP affect your CPU, we need to discuss how the RAM and CPU speeds are determined. There are 3 important settings: BCLK, Memory Multiplier, and the CPU Clock Ratio.

RAM Speed = BCLK x Memory Multiplier
CPU Speed = BCLK x CPU Clock Ratio

By default, the 1156 socket chips run with a BCLK of 133. The CPU and RAM attain different speeds by using different multipliers.

The Max Memory Multiplier that is available to the i5 750 chip is one that allows RAM to reach a speed of 1333 MHz at default BCLK. Doing the math, this is basically 10 (some boards treat it differently, but fundamentally it can be thought of as 10) because 133 BCLK x 10 Memory Multiplier = 1333 MHz.

The Max Memory Multiplier that is available to the i7 8xx chips is one that allows RAM to reach a speed of 1600 MHz at default BCLK. Doing the math, this is essentially 12 because 133 BCLK x 12 Memory Multiplier = 1600 MHz.

The i5 750 runs with a default CPU Clock Ratio of 20. This gives it it's default CPU speed of 133 BCLK x 20 CPU Clock Ratio = 2.66 GHz. When XMP is turned on for 1600 MHz RAM, the BCLK is usually changed to 160**. Remember, the max memory multiplier available to the i5 750 is 10, so to hit 1600 MHz the motherboard must change the BCLK to: 1600 / 10 = 160.

(The i7 860 runs with a default CPU Clock Ratio of 21. This gives it it's default CPU speed of 133 BCLK x 21 CPU Clock Ratio = 2.80 GHz.)

As a result of this BCLK change, the CPU speed changes. If the CPU Clock Ratio did not change your CPU would be OCed to 20 x 160 = 3.2 GHz. Most (if not all) motherboards would deem this too dangerous to allow when a user only flips the XMP profile. So, the boards drop the CPU Clock Ratio in response to the raised BCLK. Based on what I've seen around the forum, most boards will drop the CPU Clock Ratio to 17. This means your CPU is running at a speed of 17 * 160 = 2.72 GHz.

I don't know how Asus or others handle this, but Gigabyte treats this change as an OC. If you have left other settings as is, they will disable Turbo, EIST, and Sleep States. These functions can be turned back on, but you have to go in and flip the settings from "Auto" to "Enabled". "Auto" means the motherboard decides whether or not to allow these functions. By setting it to "enabled" you ensure that they are always available.

Of course once you have XMP turned on and your BLCK gets bumped up to 160, if you enable Turbo it will run your machine even faster. When Turbo kicks in, the CPU Clock Ratio changes. For example, with one core of an i5 750 active Turbo might raise the CPU Clock Ratio as high 24. This gives a stock CPU a max speed of 133 BCLK x 24 CPU Clock Ratio = 3.20 GHz. But with XMP on and a BCLK of 160, your new max speed is 160 x 24 = 3.84 GHz. You'll want to test your system for stability running at these settings. Keep an eye on V and heat.


Putting this all together, at default/stock for an i5 750 we have:
BCLK = 133
Memory Multiplier (effectively) = 10
CPU Clock Ratio = 20

RAM Speed = BCLK x Memory Multiplier = 133 x 10 = 1333 MHz
CPU Speed = BCLK x CPU Clock Ratio = 133 x 20 = 2.66 GHz

When Turbo kicks in (for example, let's say it is at it's max):
BCLK = 133
Memory Multiplier (effectively) = 10
CPU Clock Ratio = 24

RAM Speed = BCLK x Memory Multiplier = 133 x 10 = 1333 MHz
CPU Speed = BCLK x CPU Clock Ratio = 133 x 24 = 3.20 GHz


With 1600 RAM and XMP on**:
BCLK = 160
Memory Multiplier (effectively) = 10
CPU Clock Ratio = 17

RAM Speed = BCLK x Memory Multiplier = 160 x 10 = 1600 MHz
CPU Speed = BCLK x CPU Clock Ratio = 160 x 17 = 2.72 GHz

Turbo will only work if the CPU Clock Ratio is set to 20. So if you turn on XMP, and you enable Turbo and change the CPU Clock Ratio:
With 1600 RAM and XMP on, when Turbo kicks in (for example, let's say it is at it's max):
BCLK = 160
Memory Multiplier (effectively) = 10
CPU Clock Ratio = 24

RAM Speed = BCLK x Memory Multiplier = 160 x 10 = 1600 MHz
CPU Speed = BCLK x CPU Clock Ratio = 160 x 24 = 3.84 GHz

**It's possible when you turn XMP on some boards may not change the BCLK to 160 and the CPU multiplier to 17 and Turbo off. But so far that has been my observation. Let me know if you find anything different.
Share
a b à CPUs
February 1, 2010 12:41:24 AM

All that being said, if you are not interested in OCing your CPU, and you want to keep the Turbo feature you paid for, turn XMP off. Manually set the timings and voltage for your RAM to their rated spec, but let it run at 1333 MHz. The performance difference is fairly negligible anyway. If you want to tweak and test the RAM, you could try lowering the timings or V since you are not running at 1600 MHz. But definitely test for stability.

And if you do want to OC, you should do that by hand anyway, and not using XMP.
m
0
l
February 1, 2010 4:08:39 AM

Best answer selected by tooocoool.
m
0
l
a b à CPUs
February 1, 2010 6:21:19 AM

I THINK SOMEBODY FORGOT TO ( " " ) ......
m
0
l
a b à CPUs
February 1, 2010 10:38:02 AM

Forgot to what? That's my explanation, determined after many many hours of tweaking and testing my board and working with others on this forum.
m
0
l
April 11, 2010 2:36:55 AM

I also have an Asus p7p55-m, i5 750 and 2x2GB gskill 1600. When I enable the turbo function to auto overclock the cpu without editing the BIOS I've noticed the performance drops, the sound in some games gets choppy and out of sync and get less 10 fps average making this feature kind of useless.

Using XMP in bios to increase the ram clock to 1600 the bclk gets fixed at 160x17 with a clock somewere around 2719MHz. The cpu temp is now at 49º/50ºC with the stock cooler and the performance increased.

Is it safe or possible to get it to 3.8Ghz stable with this motherboard with a decent cooler? and how can I change the memory multiplyer to make it 160x24?
m
0
l
April 11, 2010 2:46:50 AM

I meant cpu clock ratio to 160x24 not memory multiplier, sorry I'm new to this :p 
m
0
l
a b à CPUs
April 11, 2010 7:34:33 PM

zilaan said:
When I enable the turbo function to auto overclock the cpu without editing the BIOS I've noticed the performance drops, the sound in some games gets choppy and out of sync and get less 10 fps average making this feature kind of useless.

Is it safe or possible to get it to 3.8Ghz stable with this motherboard with a decent cooler? and how can I change the memory multiplyer to make it 160x24?

If you're having OC problems and for OC advice, I recommend starting a new thread in the Overclocking Forum found here: http://www.tomshardware.co.uk/forum/forum-11.html
m
0
l
April 11, 2010 7:47:08 PM

ekoostik said:
If you're having OC problems and for OC advice, I recommend starting a new thread in the Overclocking Forum found here: http://www.tomshardware.co.uk/forum/forum-11.html


Ok, I found where the problem was and got it figured out, now running at 160x19 (3040MHz) Vcore 1.28, 45ºC idle and 56ºC load, with stock cooler. I'll just get a new cooler and try to reach 160x24. At 160x20 it gets too hot 65ºC at load... I think it's too hot because asus pc probe started the alarm sound. Thanks anyway ekoostik, your information was very usefull.
m
0
l
May 28, 2010 6:25:39 PM

Hi,
I have the same processor and the motherboard (GA-P55M-UD2 and i7-860) as you. You mentioned in the forum that if i enable XMP in the BIOS, i have to switch the Turbo, EIST, Sleep modes from "Auto" to "Enable". I am just wondering, by these settings do you mean all of them in the processor settings page or just the ones you mentioned?
Also, how do I see / check that the memory modules are indeed running at 1600MHz?
m
0
l
a b à CPUs
May 28, 2010 6:36:12 PM

I would set all of them to Enabled. If there is anything you don't want, specifically Disable it. No reason to leave anything on the Processor Settings page set to Auto.

To check what speed your RAM is operatin at, download CPU-Z: http://www.cpuid.com/softwares/cpu-z/versions-history.h...

Run CPU-Z, go to the memory tab, and double whatever is reported in the DRAM Frequency.

You can also use the CPU tab to see what frequency your CPU is running at at any given time.
m
0
l
!