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Gskill and GA P55A-UD3

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March 19, 2010 3:48:03 PM

I have a Gigabyte GA-P55A-UD3 motherboard. I did some researching on the net about the memory that's compatible with this motherboard. I prefer purchasing this memory (G.SKILL 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Dual Channel Kit Desktop Memory F3-12800CL9D-4GBNQ). I was doing research on this memory. An end user has the same mobo that I have and he purchased this memory. I think he was instructed to change the memory speed on the bios settings so that it would recognize the memory's actual speed.

I just wanted to find out if this memory is compatible with my motherboard. If not what brand of memory do you guys recommend. Do I also have to edit my bios settings so that this memory would run of a speed of 1600 instead of 1333?

Thank you.

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March 19, 2010 10:13:37 PM

How about Kingston memory. I plan of just getting that one.
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March 19, 2010 10:36:46 PM

What CPU are you getting?
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March 19, 2010 11:25:58 PM

dennis2 said:
How about Kingston memory. I plan of just getting that one.


Kingston also makes good RAM. Did you have a specific model picked out?
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March 20, 2010 1:11:36 AM

KHX1600C9D3K2/4G <--- this model. Do I still have to configure my bios settings for this particular brand of ram?
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March 20, 2010 1:29:47 AM

It's the same situation as the G.Skill RAM. Each BIOS handles RAM differently, so it's hard to tell. It is compatible with the motherboard. The G.Skill is probably the better choice, as it is lower voltage.
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March 20, 2010 2:12:07 AM

What CPU are you using?

You are getting 1600 RAM - if you want to run your RAM at 1600 MHz then Yes, you will have to configure your settings in BIOS.

If you have an i7 860 or i7 870, you can change your memory multiplier to 12 to get it to run at 1600.

If you have an i3 or i5 chip, the max memory multiplier you will be able to select is 10. This means to set the frequency higher than 1333 MHz you'll have to do more work in BIOS and OC your CPU, or alternatively up your memory and lower your CPU to balance the change while making other trade offs, such as losing turbo.
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March 20, 2010 2:30:33 AM

Gigabyte BIOSes (and ram manufacturers) usually set the ram low and with loose timings at default for compatibility reasons. Setting it in the BIOS is not a big deal. We can help you with that when the time comes.
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March 20, 2010 8:19:30 PM

Thanks. I have an core i5-750 cpu that's intalled to a Gigabyte GA-P55-UD3. Even if I'm not doing any overclocking. Would I have a problem if I adjust the memory speed to 1600?
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March 20, 2010 8:58:42 PM

With an i5 750, the max memory multiplier you have available is x10. This means to run your RAM at 1600 you'll have to raise your blck to 160. This will OC your CPU.

The i5 750 cannot run with RAM faster than 1333 MHz without OCing or making trade-offs.

There can still be good reasons to get 1600 RAM instead of 1333 RAM. For example, for whatever reason the 1600 RAM is often cheaper than 1333 MHz RAM. There's also very little performance difference between the two frequencies so buying 1600 RAM and running it at 1333 RAM is not that big a deal. Here's an article that is worth reading:
http://www.tomshardware.com/reviews/core-i7-870-1156,24...

If you're interested in why the i5 750 cannot run with RAM faster than 1333 MHz without OCing or making trade-offs, here's the long explanation:


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 may differ 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. If you try and find anything different, please let me know.
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March 20, 2010 8:59:01 PM

You dont have to OC per se, but you do have to increase the BCLK to 160 (since mem multi is 10.0 max) and then lower the multipliers for core clock etc to compensate.
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March 20, 2010 9:16:18 PM

EXT64 said:
You dont have to OC per se, but you do have to increase the BCLK to 160 (since mem multi is 10.0 max) and then lower the multipliers for core clock etc to compensate.

This is certainly true, and that is exaclty what happens when XMP is enabled (on RAM that allow it). But in my experience, there are side effects. The biggest one being that this will result in losing Turbo. Many people do this on accident never even realizing that to get the minmal boost in RAM performance they have turned off Turbo. This is the main "tade-off" that I was referring to.

EDIT: From what I have seen and read, to keep Turbo you have to keep your multiplier at 20 (for the i5 750). If anyone has seen anything to the contrary, I'm always the first to admit I don't know everything. But in conversation with others here in these forums I haven't seen evidence against this.
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March 21, 2010 12:28:32 AM

This is somehow complicated. I'll just stick with a DDR3 1333 ram. Any recommendations? As long as it's a DDR 1333 it is compatible with my Gigabyte GA-P55A-UD3 mobo right?
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March 21, 2010 12:31:21 AM

This is what I plan to buy instead for my motherboard. The Patriot PGV34G1333ELK DDR3 1333 (PC3 10666). Would this be compatible with my board?
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March 21, 2010 12:35:13 AM

Yes, that model is also compatible with your motherboard.
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March 21, 2010 2:01:15 AM

That's fine but just as a note, you don't have to get 1333MHz ram. 1600+ ram will run just fine at 1333, which is what I was doing until I did my very light OC. And also going along with Turbo, I had to set my voltage to Auto to get it to work past the first level once I OC'ed.
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March 21, 2010 12:44:37 PM

Thanks chief
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March 21, 2010 5:42:02 PM

Another memory that I plan to buy is this one Corsair TW3X4G1333C9A DDR 1333 4GB (2x2). I saw this memory available at Frys. The reason why I want to buy this at Fry's is that I've been reading feedbacks on newegg about the memory that they sell. I usually read the negative feedbacks. Some customers usually get a BSOD the first time they install Windows on their computer. They have to RMA the product to Newegg or to the manufacturer. If this happens to me, I just want to return right away to Fry's and get a replacement. I've been upgrading memory on my computers for about 15 years now. So far I never encountered any BSOD on my old computers :) 
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March 21, 2010 5:46:47 PM

You've got to take the newegg reviews with a grain of salt. Most of the people that are leaving reviews, don't have the technical knowledge on how to properly diagnose a problem. They just blame what they think is causing the problem.
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March 22, 2010 5:26:30 PM

I have to agree with you on that one.
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March 22, 2010 6:48:04 PM

Yes, 95% (wonderful fake statistic) of the negative reviews I see on newegg about memory are because the person did not take 15 seconds to properly set the ram. That said, ram is defective now and then, but it is not a huge deal.
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March 23, 2010 2:02:45 AM

Yes
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