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Core i7 920 and DDR-1333 memory

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a b V Motherboard
a b } Memory
July 10, 2009 8:19:33 PM

I'm planning a new Core i7 920 system based on an ASUS P6T motherboard. I'm not interested in overclocking the CPU. Intel states that the fastest supported memory is DDR3-1066 but I've read that DDR3-1333 should work as well.

With DDR3-1333 memory installed, will the motherboard automatically configure everything so that it will work, or will I have to configure something manually?
July 10, 2009 9:36:03 PM

sminlal said:
I'm planning a new Core i7 920 system based on an ASUS P6T motherboard. I'm not interested in overclocking the CPU. Intel states that the fastest supported memory is DDR3-1066 but I've read that DDR3-1333 should work as well.

With DDR3-1333 memory installed, will the motherboard automatically configure everything so that it will work, or will I have to configure something manually?


No, without OC the i7 runs at 1066. See here: http://www.intel.com/support/processors/sb/CS-029913.ht...

Most mobos let you independently adjust the memory multiplier. The base clock frequency is 133MHz. 1066MHz / 133MHz = 8.
1333/133 = 10. So to effectively use your memory, you need to go into the BIOS and change the memory multiplier from 8 to 10.

Or you could try increasing the base clock until the memory multiplier becomes 10 but you didn't want to over clock .....

Take a look here:

http://www.computerpoweruser.com/editorial/article.asp?...

Mike
a b V Motherboard
a b } Memory
July 10, 2009 10:12:06 PM

MikeJRamsey said:
No, without OC the i7 runs at 1066. See here: http://www.intel.com/support/processors/sb/CS-029913.ht...

Most mobos let you independently adjust the memory multiplier. The base clock frequency is 133MHz. 1066MHz / 133MHz = 8.
1333/133 = 10. So to effectively use your memory, you need to go into the BIOS and change the memory multiplier from 8 to 10.


Thanks Mike! I'm not terribly concerned about getting 1333 performance out of the 1333 memory, what's more important to me is just how to make sure it will work with the i7. The point I'm somewhat confused about is how the memory multiplier gets set in the first place.

If you can adjust it in the BIOS, then I'm thinking that the BIOS must set it. And if the BIOS sets it, what value does it use by default? I'm thinking it might read the SPD info from the DIMMs and set the multiplier to achieve the 1333 frequency.

Or is the multiplier initially set by the CPU and not touched by the BIOS unless you've entered a specific overriding value?
Related resources
July 11, 2009 2:27:39 AM

Siminlal,
Please read the two links that I provided. From the first,
"What is the maximum frequency for DDR3 memory when used with Intel® Core™ i7 desktop processors?

These processors support DDR3 memory with a maximum frequency of 1066 MHz. If faster DDR3 memory is used (such as 1333 MHz or 1600 MHz), it will be down-clocked to operate at 1066 MHz."

The SPD is used to make sure that memory slower than 1066 is read at the correct number of cycles. But the adjustment upwards stops at 1066. So by default, if your memory supports it, the speed is 1066.

Summing up, the CPU will down clock your memory but will not up clock it past 1066. For that, you need to tinker with the BIOS.

Hence the 2nd link.

Really, read the links. :) 

Mike
a b Ĉ ASUS
a c 244 V Motherboard
a c 105 } Memory
July 11, 2009 2:29:32 AM

For any ram you are considering, do your own homework.
Go to the ram vendor's web site, and access their configurator.
Corsair, Kingston, Patriot, OCZ and others have them.
Their compatibility list is more current than the motherboard vendor's QVL lists which rarely get updated.
Enter your mobo or PC, and get a list of compatible ram sticks.

Here are a few links:

http://www.crucial.com/index.aspx

http://www.corsair.com/configurator/default.aspx

http://kingston.com/

http://conf.ocztechnology.com/index.php?c=1

Cpu performance is not very sensitive to ram speeds.
If you look at real application and game benchmarks(vs. synthetic tests),
you will see negligible difference in performance between the slowest DDR2 and the fastest DDR3 ram.
Perhaps 1-2%. Not worth it to me.
Don't pay extra for faster ram or better timings unless you are a maximum overclocker.

The P6T bios will select a running configuration if you leave everything on default or auto.
Even if you wish to overclock a bit, the bios will set the ram as best it can. For a simple overclock to 3.0 just raise the BCLK value from 133 to 150,and leave the ram at auto.
a b V Motherboard
a b } Memory
July 11, 2009 2:40:46 AM

MikeJRamsey said:
Siminlal,
Please read the two links that I provided. From the first,
"What is the maximum frequency for DDR3 memory when used with Intel® Core™ i7 desktop processors?

The SPD is used to make sure that memory slower than 1066 is read at the correct number of cycles. But the adjustment upwards stops at 1066. So by default, if your memory supports it, the speed is 1066.

Mike

Thanks again, Mike. I did have a look at the links - unfortunately the ComputerPowerUser site tells me I need to be paid subscriber to see the article you linked to. Not to worry, though - you've told me what I needed to hear.


geofelt said:
The P6T bios will select a running configuration if you leave everything on default or auto.

Thanks, geofelt! Sounds like I don't have anything to worry about.
July 11, 2009 3:41:37 AM

sminlal said:
Thanks again, Mike. I did have a look at the links - unfortunately the ComputerPowerUser site tells me I need to be paid subscriber to see the article you linked to. Not to worry, though - you've told me what I needed to hear.

[snip].


Wow. I am not a paid subscriber. I wonder what's up with that? Take a look here then:
http://www.tomshardware.com/forum/forum2.php?config=tom...

I agree with geofelt that memory speed is not the most critical thing to worry about. To get a feel, take a look at this:
http://www.tomshardware.com/reviews/core-memory-scaling...

Cheat and read the conclusion first, then go back and look at the charts. :) 

I was where you are now back when I started looking into this subject. Memory is not going suck tons of energy nor generate lots of heat when you increase its multiplier. For this reason, I would just do it.
a b V Motherboard
a b } Memory
July 11, 2009 4:19:57 AM

sminlal said:
I'm planning a new Core i7 920 system based on an ASUS P6T motherboard. I'm not interested in overclocking the CPU. Intel states that the fastest supported memory is DDR3-1066 but I've read that DDR3-1333 should work as well.

With DDR3-1333 memory installed, will the motherboard automatically configure everything so that it will work, or will I have to configure something manually?


Depending on how the memory is programmed...

Depending on how the MEMORY is programmed...

Depending on how the MEMORY, not the processor, is programmed...

It could fire up and operate at DDR3-1333. That's because Asus BIOS is smart enough to know this stuff. Intel "rates" some processors at 1066 and others at 1333 max, but Asus knows they can all run 1333.
July 11, 2009 11:10:59 AM

Crashman said:
Depending on how the memory is programmed...

Depending on how the MEMORY is programmed...

Depending on how the MEMORY, not the processor, is programmed...

It could fire up and operate at DDR3-1333. That's because Asus BIOS is smart enough to know this stuff. Intel "rates" some processors at 1066 and others at 1333 max, but Asus knows they can all run 1333.


Ah, so even though the Intel FAQ is on i7 processors, the question was answered in the context of the Intel Desktop mobo DX58SO. Other mobos handle it differently. Luck is an acronym for Laboring Under Correct Knowledge. You just made me luckier.

Thanks Crashman. :) 

EDIT: Because I hate to be unlucky, I did some more digging and came up with Extreme Memory Profiles (XMP). Given the following
  • memory supports XMP
  • mobo supports XMP
  • you enable the XMP functionality in the BIOS
  • you select one of the available profiles

    the BIOS will read the XMP data stored in the chip's SPD and optimally set the

  • system memory multiplier
  • memory frequency
  • memory voltage
    for the specified profile.

    That is just way cool.

    Mike
    a b V Motherboard
    a b } Memory
    July 12, 2009 2:26:27 AM

    Crashman said:
    It could fire up and operate at DDR3-1333. That's because Asus BIOS is smart enough to know this stuff. Intel "rates" some processors at 1066 and others at 1333 max, but Asus knows they can all run 1333.

    Thanks Crashman! So I take this to mean that even though Intel says that the processor caps the speed at 1066, that may only apply to the initialization of the processor by itself - once the processor has completed it's own powerup sequence the motherboard can come along and apply it's own values. All of which makes perfect sense, otherwise overclocking wouldn't be possible.

    I've looked in the Asus motherboard manuals, and the closest I can find to information on this subject is in the "Tweaker Menu" section under "DRAM Frequency". Here it lists some of the options, including "Auto" - but unfortunately it doesn't say what "Auto" actually does - whether it sets the memory's SPD-defined speed or just leaves the speed set by the CPU (which for the Core i7 920 would be 1066) without changing it.

    MikeJRamsey said:
    Because I hate to be unlucky, I did some more digging and came up with Extreme Memory Profiles (XMP).

    That's interesting - I learn something more with each post. It looks like XMP is just another level of SPD information on the DIMMs, which still begs the question of what the motherboard will do with it. The Asus motherboard manual says that it "supports XMP", but then it doesn't actually refer to "XMP" anywhere in the manual aside from listing support for specific XMP-enabled DIMMs.
    a b Ĉ ASUS
    a c 244 V Motherboard
    a c 105 } Memory
    July 12, 2009 2:48:01 AM

    Perhaps an example can help. With a P6T deluxe, I changed the BCLK from 133 to 160 giving 3.2. Everything else was left to default or auto.
    My ram is patriot 1600.
    In cpu-Z under SPD it shows XMP-1600 800mhz, 9.0-9-24-38-2T and 1.65 volts. That is the max for the ram.
    Also under spd there are two jedc#
    457mhz,6.0-6-6-18-24 -1.5v
    533 mhz, 7.0-7-7-20-27-1.5v
    ---------------------------------------------
    the result under memory, which is what is actually running:
    dram frequency=480.0
    fsb to dram 2:6 I think this means that my ram is operating at 1440, somewhat below it's maximum.
    cas 4.0 clocks
    ras to cas delay 6 clocks
    ras precharge 6 clocks
    cycle time 18 clocks
    command rate 1T

    As I recall, the result voltage is also 1.5
    !