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Gigabyte GA MA790FXT-UD5P and 1.8V memory modules

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September 14, 2009 2:01:18 PM

Will Gigabyte GA MA790FXT-UD5P work out of the box with memory modules rated at 1.8V?

If not, can anyone suggest the best way to get around this problem?

I can get hold of a standard 1.5V memory module but I'll be using a pretty large CPU cooler (Prolimatech Megahalems) so RAM swapping can be really inconvenient. I'd really appreciate it if someone can suggest a simple solution to this problem.

Thanks in advance
a b } Memory
a c 177 V Motherboard
September 14, 2009 3:04:24 PM

JEDEC specs DDR3 at 1.5V; page 43 of the GB manual states:

"DDR3 Voltage Control
Allows you to set memory voltage.
Normal -Supplies the memory voltage as required. (Default)
+0.05V ~ +0.75V Increases memory voltage by 0.05V to 0.75V at 0.05V increment."

So, 1.5 + .75 means you can set the RAM as high as 2.25V in the BIOS...
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September 14, 2009 3:11:05 PM

Thanks for the prompt reply; I'm aware that I can set the voltage through BIOS but what I'm really asking is do I need to use 1.5V memory just to reach BIOS for the first ever boot, or will the 1.8V memory work just fine?
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a b } Memory
a c 177 V Motherboard
September 14, 2009 4:32:59 PM

During the build, put one stick of RAM in the slot nearest the CPU; go into the BIOS, and execute the "Load Optimized Defaults"; this will set your board up for your specific RAM. If you intend to use mare than two sticks, we will need to tweak further...
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September 14, 2009 8:23:36 PM

This is going to sound really silly, but can the system boot if I put one stick of ram anywhere EXCEPT the slot nearest the CPU socket? If by any chance this is possible, I'll have the freedom to align the CPU cooler so that it blows air upwards, and I won't have to take it out to remove the RAM stick closest to the CPU socket.

You can take a look at the schematics for the CPU cooler here: http://www.prolimatech.com/products/megahalems.html under the tab "3D Drawing"

I also know for sure that in dual-channel config I can put 2 RAM sticks at the slots furthest away from the CPU based on this thread here: http://www.ocztechnologyforum.com/forum/showthread.php?... but I'm not sure if this holds true for a single stick config
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September 14, 2009 8:34:59 PM

Oh, one more thing, I'll be using a standard sized RAM module (1.18" tall) instead of the OCZ reapers
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a b } Memory
a c 177 V Motherboard
September 14, 2009 9:49:57 PM

One lone stck should work in any slot; I always tell people to use the first one as it minimizes skew, and should be the easiest slot to get working. Memory is made to JEDEC specifications:
http://www.jedec.org/
It contains a little piece of EEPROM memory called an SPD - this contains a set of parameters that 'tell' the motherboard how to 'set itself' to accomodate the memory; all memory is basically JEDEC spec'd RAM; DDR2 has a standard voltage of 1.8V; DDR3 is 1.5V; all memory is required to run, as a minimum, at that specified voltage. What is done is, when a memory manufacturer designs a module for higher speeds, they often specify a higher voltage to achieve that higher data rate - but - it still must meet JEDEC spec - it must run low speed at the JEDEC voltage. I don't have anything here that runs DDR3, so this is the SPD from a piece of DDR2 - the principle is the same:

Note that for the first three table entries, the voltage is 1.8V - this is the JEDEC specification for DDR2, and it must boot at that voltage. Now, look at the table in the fourth slot, labelled EPP#1; this is the set of parameters for my RAM to run at higher speed, and you can see that this is spec'd at 2.1V
The "Load Optimized Defaults" option in your BIOS forces the BIOS to read this higher voltage/speed info and set itself accordingly; these settings will then work for all four slots.
So, yes, the initial boot will work, as it can run any memory at JEDEC voltage and specs, which all memory must meet...
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September 14, 2009 10:16:04 PM

Just to check that I understood you right: 1.8V DDR3 RAM modules should work on the 790FXT-UD5P board without having to resort 1.5V DDR3 RAM first so long as the board and memory follow (the relevant) JEDEC standards; is this correct?
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Best solution

a b } Memory
a c 177 V Motherboard
September 14, 2009 10:26:34 PM

This is correct - it will boot at 1.5, and then, by executing the "Load Optimized Defaults" in the BIOS, you can adjust for the higher speed/voltage without further tinkering...
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September 14, 2009 10:30:01 PM

Awesome! Thanks man, you're a real lifesaver!
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a b } Memory
a c 177 V Motherboard
September 14, 2009 11:32:56 PM

Always welcome!

Bill
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