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Dual Channel memory compatibility

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March 18, 2010 5:36:16 PM

Hi, ive recently got my pc back from a repair shop and they said one of my ram is faulty.

So i want to get another ram to replace it BUT i heard you can't put two sticks of ram into a pc unless they are identical? my working ram is 1gb, 667mhz, so if i buy another 1gb 667 mhz would it work in dual channel?


Also, do i even NEED dual channel? some people say single channel is pretty good anyway, im playing games at the moment, stuff like bioshock2 and l4d2.
March 18, 2010 5:50:43 PM

For dual channel you need a matched pair usually packaged together as a kit. If you use different manufacturer but same speed, timings, voltage, it's possible it can work as dual channel but doubtful IMO.

Dual channel makes your system generally perform about 3%to 5% faster depending on the application (very rough estimate).

For more info:
http://en.wikipedia.org/wiki/Dual-channel


March 18, 2010 5:54:30 PM

The stats may say 3-5% faster, but in my experience, dual-channel RAM is a substantial performance increase over single-channel.

As far as using a similar stick with the one you already have, you'd be better off just buying a new 2- or 4-GB kit. DDR2 is relatively cheap now, and you can be sure that if you buy a kit that contains both sticks, they will work together (barring a defect from the factory).
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a b } Memory
March 18, 2010 7:13:49 PM

Kakazen,

There are always varying opinions on performance gain when enabling dual channel, but the truth is nobody can personally guarantee how much difference you will notice.

Is there really a difference? Yes.

The genuine intent of dual channel and now triple channel, is to reduce, if not eliminate the bottleneck that occurs when the FSB of the CPU is greater than the FSB of the RAM.

Rules to Enable Dual Channel Mode
To achieve Dual Channel mode, the following conditions must be met:

Matched DIMM configuration in each channel
Same Density (128MB, 256MB, 512MB, etc.)
Matched in both Channel A and Channel B memory channels*
Populate symmetrical memory slots (Slot 0 or Slot 1)
Configurations that do not match the above conditions will revert to Single Channel mode.

The following conditions do not need to be met:
Same brand
Same timing specifications
Same DDR speed
Memory channel speed is determined by the slowest DIMM module populated in the system.

*This really depends on your motherboard. Some manufacturers use a color-coded system (meaning use the same colors) and some require that you use the symmetrical approach (meaning same slot on both channels).
To address your concerns about RAM, know that it is recommended to use a matching pair, but not required. If you do mix RAM consider these points:

1. Make sure that all of the modules can operate safely at the highest voltage recommendation of the set. For example, if you have two modules with different voltage recommendations; 1.5v and 1.7v. Check with manufacturer to see if the 1.5v module can operate at 1.7v.

2. When it comes to speed, you can only operate at the lower speed of the set. This is due to physical limitation. For example: Two modules; one has a speed of 667MHz, the other is 800MHz. You will only be able to use up to 667MHz on the faster module.

3. Latency should be set at the higher rating of the set. Again, this is because of physical limitations. You expect to hold 2 gallons of water in a 1 gallon capacity pitcher, would you?

Generally, if you can avoid mixing, you'll find yourself with better results. Reduce as much complication as you can by having matching pairs.


March 20, 2010 5:42:57 PM

T_T said:
Kakazen,

There are always varying opinions on performance gain when enabling dual channel, but the truth is nobody can personally guarantee how much difference you will notice.

Is there really a difference? Yes.

The genuine intent of dual channel and now triple channel, is to reduce, if not eliminate the bottleneck that occurs when the FSB of the CPU is greater than the FSB of the RAM.

Rules to Enable Dual Channel Mode
To achieve Dual Channel mode, the following conditions must be met:

Matched DIMM configuration in each channel
Same Density (128MB, 256MB, 512MB, etc.)
Matched in both Channel A and Channel B memory channels*
Populate symmetrical memory slots (Slot 0 or Slot 1)
Configurations that do not match the above conditions will revert to Single Channel mode.

The following conditions do not need to be met:
Same brand
Same timing specifications
Same DDR speed
Memory channel speed is determined by the slowest DIMM module populated in the system.

*This really depends on your motherboard. Some manufacturers use a color-coded system (meaning use the same colors) and some require that you use the symmetrical approach (meaning same slot on both channels).
To address your concerns about RAM, know that it is recommended to use a matching pair, but not required. If you do mix RAM consider these points:

1. Make sure that all of the modules can operate safely at the highest voltage recommendation of the set. For example, if you have two modules with different voltage recommendations; 1.5v and 1.7v. Check with manufacturer to see if the 1.5v module can operate at 1.7v.

2. When it comes to speed, you can only operate at the lower speed of the set. This is due to physical limitation. For example: Two modules; one has a speed of 667MHz, the other is 800MHz. You will only be able to use up to 667MHz on the faster module.

3. Latency should be set at the higher rating of the set. Again, this is because of physical limitations. You expect to hold 2 gallons of water in a 1 gallon capacity pitcher, would you?

Generally, if you can avoid mixing, you'll find yourself with better results. Reduce as much complication as you can by having matching pairs.



Great answer T_T, but i was wondering what you mean by modules, as in ram slots or the ram?
Also i have vista 32bit, is it worth getting matching pairs of 2gb ram? adding up to 4gb, i think my motherboards limit is 667mhz cause it says 667mhz on the bits next to my ramslots

my processor is 2.4 core duo and gfx card is hd4850
a b } Memory
March 22, 2010 5:12:16 PM

Modules = sticks.

As for the 2x2GB...

Because of the limitations of a 32-bit operating system, you won't get to use or even see the 4GB. The most I ever saw on my own system was 3.75 GB with 2x2GB RAM modules installed on an XP 32-bit.

So is it worthwhile to get a 2x2GB RAM combo?

Yes, because you'll have the matching pair to enable your dual channel configuration with better results than you would having a mixed pair, or if you choose to upgrade to a 64-bit operating system where you can utilize your 4GB.

No, because of your OS. XP, Vista, & 7 have the same limitation in their respective 32-bit versions.
March 23, 2010 6:03:45 PM

T_T said:
Modules = sticks.

As for the 2x2GB...

Because of the limitations of a 32-bit operating system, you won't get to use or even see the 4GB. The most I ever saw on my own system was 3.75 GB with 2x2GB RAM modules installed on an XP 32-bit.

So is it worthwhile to get a 2x2GB RAM combo?

Yes, because you'll have the matching pair to enable your dual channel configuration with better results than you would having a mixed pair, or if you choose to upgrade to a 64-bit operating system where you can utilize your 4GB.

No, because of your OS. XP, Vista, & 7 have the same limitation in their respective 32-bit versions.


oh ok, what if i kept my current 1gb ram, and bought a PAIR of 667mhz 1gb ram, making my system 3gb ram. would the 1gb ram thats working by itself create a bottleneck for my pair or new ram? also think .

my mobo is conroexfire-esata2, supports 667mhz with 2 pairs of dual channel slots.
do motherboards have ram voltage 'limits'?
a b } Memory
March 23, 2010 8:39:28 PM

Theoretically no, it shouldn't bottleneck. Remember, the bottleneck occurs when your CPU FSB is greater than the memory controller FSB. If you're using 3 sticks of RAM, you should be more concerned with the dual channel mode caveat.

Look back on my post about the rules to dual channel configuration. Notice that the requirment is for matching density or memory capacity.

The caveat is that if you have unmatched density in a dual channel set up, you'll use the higher density in the dual channel, but the remaining density will automatically be mapped into single channel.

Let's use your question as the example, but slightly modify it. Let's say instead of 1 x 1GB as your original set up, you have 2 x 512MB instead. If you use the 2 x 512MB + 2 x GB that you plan to buy, you'll still have a dual channel set up, technically. However, due to the memory mapping, you'll only have 2GB of dual channel, because the remaining 1GB is remapped to single channel. Again, this happens when you don't match density.


Now to answer you voltage question. Yes, every motherboard has a limit to what you can set the voltage to. The limitations are in the BIOS. For example, let's say your BIOS shows that you can increase the voltage to 1.9 v as the highest. If that were the case, you don't want to buy OCZ Technology RAM, as they usually require 2.0 -2.2 v.
March 24, 2010 2:52:59 PM

T_T said:
Theoretically no, it shouldn't bottleneck. Remember, the bottleneck occurs when your CPU FSB is greater than the memory controller FSB. If you're using 3 sticks of RAM, you should be more concerned with the dual channel mode caveat.

Look back on my post about the rules to dual channel configuration. Notice that the requirment is for matching density or memory capacity.

The caveat is that if you have unmatched density in a dual channel set up, you'll use the higher density in the dual channel, but the remaining density will automatically be mapped into single channel.

Let's use your question as the example, but slightly modify it. Let's say instead of 1 x 1GB as your original set up, you have 2 x 512MB instead. If you use the 2 x 512MB + 2 x GB that you plan to buy, you'll still have a dual channel set up, technically. However, due to the memory mapping, you'll only have 2GB of dual channel, because the remaining 1GB is remapped to single channel. Again, this happens when you don't match density.


Now to answer you voltage question. Yes, every motherboard has a limit to what you can set the voltage to. The limitations are in the BIOS. For example, let's say your BIOS shows that you can increase the voltage to 1.9 v as the highest. If that were the case, you don't want to buy OCZ Technology RAM, as they usually require 2.0 -2.2 v.


ok, hmm well on this page showing my motherboardhttp://www.asrock.com/mb/overview.asp?Model=ConRoeXFire... it doesn't specify my voltage limit for ram, do you know what it is for my board conroexfire-esata2?
a b } Memory
March 24, 2010 4:53:51 PM

Sorry. No, I don't know the max voltage you can set your RAM to. However, there three things to consider:

1. Check your BIOS, under the Advanced page you'll see the section called Chipset Configuration. It is here where you'll find the section to change your DRAM voltage. Whatever the max is in your BIOS is the max you can increase to.

2. Set the voltage to what the manufacturer recommends, but if you populate all four slots on your board, increase the voltage by .05v - .1v.

3. According to your motherboard manual, your board supports up to 4GB max. What this means is that if you choose to use all four slots, the most you should use per slot is 1GB. Anything else would be unused.

Good Luck
!