The computer i ask this question for is a Q6600 in a 780i with 7970, win7-64 and i seem to be suffering from bus bottle neck problems,
I am/was using two sets of Corsair dominator TWIN2X2048-8500C5D G, (its is factory overclocked 800, spd at 1066)
That reduced a little when overclocking the fsb/ram to get more throughput and only two cpu crunching.
On a heavly loaded system with a two channel memory bus and fore memory slots which would give the best throughput and memory system performance,
two 4GB sticks or fore 2GB sticks, accepting that they are all `matched` sets of ram,
or is the difference so small only synthetic benchmarks would show any difference.
I ask this as i have had one stick of a set fail recently.

... On a heavly loaded system with a two channel memory bus and fore memory slots which would give the best throughput and memory system performance,
two 4GB sticks or fore 2GB sticks, accepting that they are all `matched` sets of ram ...

You would see no measurable difference if you have the same timings. The CPU/FSB can't use any more than the two memory channels.

Hence go for whatever RAM combination gives you the best timings. You might find the 2GB can be clocked the faster, or you might find the 4GB uses more recent chips that are higher performance to give you the faster timings.


Memtest86+ is a very good tool to show you what memory bandwidth you actually get for whatever tweaks you might want to try.

Happy fast crunchin',
Martin

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A few years ago one of the review sites, possibly tomshardware but I don't recall, did such testings. With a P4 using 2 1GB or 4 512MB sticks of RAM. Their testing showed the 2 1GB sticks were a few % faster and also used less power. They were using memory with the same timings as to not skew the results.
I distinctly remember this as this was done right after I had just recently bought 4 512MB for my P4 system. So I cursed for a while after reading it.

I have not seen anyone do any sort of review since then so I'm not sure if it still applies on newer hardware.

If you are trying to do some heavy overclocking. You may be able to get a higher overclock using 2 instead of 4.

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I do remember that most motherboard manufacturers had/have a disclaimer that filling all memory slots will result in slower memory speeds.

T.A.

I do remember that most motherboard manufacturers had/have a disclaimer that filling all memory slots will result in slower memory speeds.

T.A.

Two days ago I switched 4x 2GByte Kingston HyperX 1600MHz in my i7-2600 for 2x 8GByte Kingston 1333MHz. With better timings and (less) 1.5Volt (Kingston 1600 required 1.65 to 1.85V) . (KVR1333D3N9HK4/32G PC3 10600 CL90).
Boot-time improved by a few seconds.
Apart from the double amount of RAM, it uses less power and isn't slower, I'd
say faster after trying some programs and also BOINC (7.0.25)

Should run some proper memory tests, though.
This is DDR3 RAM.

On an older system with DDR2, I put in some extra RAM 4x 2GByte, 2 sets of
2x 2GB.
This time the four sticks run at a lower frequency, 777MHz in stead of 800MHz.
Same setting, or changed nothing in BIOS.
In this system, FSB= 1555MHz., X9650@ 3.55GHz.

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Thank you for your input on this,
I have found that fast DDR2 is not as common as it used to be so choice is a bit limited,
I will go with the two sticks of 2GB, largely because there is no fore stick sets to be found, which made my question a bit redundant . . .
I have found two sets on amazon:-

KOMPUTERBAY 4GB (2X 2GB) DDR2 PC2-8900 1110MHZ DIMM 4 GB - ( 5-7-7-25 @1.8V)

GLOBAL MEMORY 4GB (2 x 2GB) DDR2 1100MHz PC2-8800 240-PIN DIMM (5-5-5-15 @1.8v)

The speed difference of 1100 vs 1110 is nothing a tiny overclock will not fix,
The timings are not vastly different but may hide better quality chips in the Global mem,
Or i may just be fooling myself,
The price, the Komputerbay costs less by a long way though i dont want to be a cheep skate and get something that may in the long run not be as good,
Though i would never know either way anyway so i will have to just dive in and hope for the best.
The choice also boils down to how often will i realy need 8GB,
I think i will make do with 4GB of `quick` ram,
Unless anyone has ever had either of the types and knows otherwise.

Thank you for your input on this,
I have found that fast DDR2 is not as common as it used to be so choice is a bit limited,
I will go with the two sticks of 2GB, largely because there is no fore stick sets to be found, which made my question a bit redundant . . .
I have found two sets on amazon:-

KOMPUTERBAY 4GB (2X 2GB) DDR2 PC2-8900 1110MHZ DIMM 4 GB - ( 5-7-7-25 @1.8V)

GLOBAL MEMORY 4GB (2 x 2GB) DDR2 1100MHz PC2-8800 240-PIN DIMM (5-5-5-15 @1.8v)

The speed difference of 1100 vs 1110 is nothing a tiny overclock will not fix,
The timings are not vastly different but may hide better quality chips in the Global mem,
Or i may just be fooling myself,
The price, the Komputerbay costs less by a long way though i dont want to be a cheep skate and get something that may in the long run not be as good,
Though i would never know either way anyway so i will have to just dive in and hope for the best.
The choice also boils down to how often will i realy need 8GB,
I think i will make do with 4GB of `quick` ram,
Unless anyone has ever had either of the types and knows otherwise.

I've only seen a 4 package, containing 2x 2x 8GByte 1333MHz.
KINGSTON KVR1333D3N9HK4/32G; PC3-10600-CL9 240pin DIMM kit (4 pcs.)
Of which I now use 2x 8GByte.

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May be off topic, but I've yet to see someone in this thread mention channels.

If you have a triple channel board for example, you would be better off with 4 sticks vs. 2. Because with 4 sticks, (one in each of 3 channels and the 4th in whichever) You will have triple channel performance. Vs. using two sticks which only affords you the speed of dual channel.

Just a thought.

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#resist

It all depends on the mobo, my friend.

Some have better subsystems than others.

My personal experience has been, the less RAM, the better for the mobo.

It seems like a better bet up front, but not in reality.

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"Time is simply the mechanism that keeps everything from happening all at once."

Hi, Ex, Like, errm its in the first post :¬) its a twin channel intel board.

Mark, I have the genral idea in my head to only fit what is `needed` whatever that realy is,
though 4GB will do ok, it has only 2GB atm and gets to 80<90% used running rosetta on the cpu plus everything else its doing.
Though it has two more PCIe @16 slots to fill if the system can handel it and when i can afford it.

Been googleing about to see if i can find anything out about this super cheep komputerbay ram,
and have decided to put it in the `you get what you pay for` group of almost unknown companies that will not last long with BOINC crunching,
Some comment say its ok, but not much more, others where DoA and after sales service was not the best,
different chips on relabeled boards sounds nasty, not for me. only a few where good to go from first post.

So i will go with the `Global Memory` whoever they are, i can not find out much about them either,
except their office is only 140 miles down the road so if things got real bad i can pay them a visit :¬)
At least their pricing gives a belivable feel to it being something that will last longer than the cheepono.

May be off topic, but I've yet to see someone in this thread mention channels.

If you have a triple channel board for example, you would be better off with 4 sticks vs. 2. Because with 4 sticks, (one in each of 3 channels and the 4th in whichever) You will have triple channel performance. Vs. using two sticks which only affords you the speed of dual channel.

Just a thought.

With a triple channel board you are better off with 3 sticks, not 4.

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Hi, Ex, Like, errm its in the first post :¬) its a twin channel intel board.

Mark, I have the genral idea in my head to only fit what is `needed` whatever that realy is,
though 4GB will do ok, it has only 2GB atm and gets to 80<90% used running rosetta on the cpu plus everything else its doing.
Though it has two more PCIe @16 slots to fill if the system can handel it and when i can afford it.

Been googleing about to see if i can find anything out about this super cheep komputerbay ram,
and have decided to put it in the `you get what you pay for` group of almost unknown companies that will not last long with BOINC crunching,
Some comment say its ok, but not much more, others where DoA and after sales service was not the best,
different chips on relabeled boards sounds nasty, not for me. only a few where good to go from first post.

So i will go with the `Global Memory` whoever they are, i can not find out much about them either,
except their office is only 140 miles down the road so if things got real bad i can pay them a visit :¬)
At least their pricing gives a belivable feel to it being something that will last longer than the cheepono.

Priced between those two 4GB kits you listed I found a kit from crucial. Not sure if it is worth looking into for you, but at least it's a name brand.

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Hi, Ex, Like, errm its in the first post :¬) its a twin channel intel board...

You are correct. Sorry about that. :-)

My work here is done.
*wipes hands together*


@Wembely:

With a triple channel board you are better off with 3 sticks, not 4.

But 4 is better than two... :-)

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#resist

@Wembely:

With a triple channel board you are better off with 3 sticks, not 4.

But 4 is better than two... :-)

Not when putting that forth stick into one of the triple channels slows down that channel :p

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Priced between those two 4GB kits you listed I found a kit from crucial. Not sure if it is worth looking into for you, but at least it's a name brand.

Thanks, that crucial set is close, though it is CL7, I would prefer a well known brand but i have set myself the target of the fastest DDR2 i can find,
and even then hope to over clock it a bit.

I am using the Kingston HyperX KHX8500D2T1K2/4G on my Asus M4N72-E mother board and with this ram at 1066 the voltage is set to 2.3 from a normal 1.8
5.5.5.15 at 2T.
The speed is slower on the B channel then the A channel.
A lot of motherboards will have the exact same problems. Depending on the placement of Ram on which channel.
Using the Coolmaster 212 Plus cooler forbids me from placing ram in the A channel because of room so I am stuck with the B channel.

Look for the proper voltage on your ram to make sure DDR2 running at 1066 is not requiring 2.2 or 2.3 volts.
It may well be that is what is going on.


A channel is always the best bet.
If you use all four then the speed will go down so up the voltage and watch temps

what i have atm is Corsair dominator TWIN2X2048-8500C5D, spd is 1066 2.1v 5-5-5-15,
though the small over clock i have on it has streched it to 1086 2.15v 5-6-6-18 and it does not want to go any faster than that,
i recon it was built on its limit in the first place,
though after five years of crunching before one failed is not bad,
I have ordered the 2x 2GB 1100 Global memory and will see what turns up and what it can do and what the timings and volts realy are.
I have no problem with clearance for the heatsink it is fitted with a Thermolab Baram 2010 the ram fits under it!!,
it is a `Tower Block` of a cooler and very good only needing a small totaly silent fan to keep cpu 55<60c,
i even tried it fanless and just the air flow through the case kept it below 70c.

From my experience the higher the Hz and if its 4 X 2gb sticks its faster because they compute together much fast than 2 X 4gb