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Synchronous vs. asynchronous Dual Channel

Synchronous vs. asynchronous Dual Channel

Many modern notebook chipsets, including all current Intel models, support synchronous dual channel operation, which means that both or all four memory modules have to be equal. Most chipsets also support asynchronous dual channel, which allows the user to mix a 1 GB DIMM and a 2 GB DIMM in order to reach a total RAM capacity of 3 GB and still run dual channel mode. While this doesn’t deliver the full performance that can be achieved in dual channel mode, it’s still faster than single channel, and we haven’t heard of issues with it. If you intend to upgrade your 1 GB of RAM by installing a 2 GB DIMM, there is nothing that stands in your way. In a worst case scenario your system will be running in single channel memory mode, which will result in a very small performance penalty.

Test Notebook: Dell Latitude D630

ram scaling notebooks

We used a modern notebook based on Intel’s 45 nm mobile processor, the Core 2 Duo T9000 family. The Dell latitude utilizes the entire Intel Centrino platform, including the GM945 mobile chipset, a Core 2 Duo T9500 (2.6 GHz) and the 4945AGN wireless solution. Since this is a business notebook, it doesn’t come with a discrete graphics solution, rather utilizing the integrated graphics unit provided by the GM965 Express chipset. Gamers won’t like this very much, but the focus of this article is the impact more memory has on battery runtime, and a graphics chip will contribute to emptying your battery quicker than a notebook with slower but more efficient integrated graphics.

The notebook also has a Hitachi TravelStar 7K160 hard drive, which isn’t a very efficient model, but offers maximum performance. The 14” WXGA+ display isn’t state of the art, but is probably a common choice today.

Since we had a good experience with Futuremark’s MobileMark 2007 and this particular notebook, we used Windows Vista Ultimate with Service Pack 1, and we patched MobileMark with patch 3 as well to be sure we have the latest software platform.

ram scaling notebooks

Dell utilizes a GM965 chipset (Santa Rosa) for its Latitude D630.

ram scaling notebooks

The Core 2 Duo T9000’s idle clock speed is 1,200 MHz, which comes from the FSB800 200 MHz base clock speed times a base multiplier of 6.


Talkback

Deleted profile 04/29/2008 6:42 AM
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I like the review and have noticed a better system, especially with vista 64 but wish we could get even more right now.
Christopher1 04/29/2008 10:14 AM
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Christopher1
The problem with getting 'even more' is that most notebook motherboards are not made to deal with more than 4GB's memory.... in fact, I think I read that there was a problem with desktop motherboards before the latest ones when you tried to put in more than 4GB's memory.
IM0001 04/29/2008 10:43 AM
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IM0001
I can for some part prove that battery life does go up with 4gb of ram. I have an older Toshiba A105-S4094 which has a Centrino Duo (pre Core 2 tech) T2250 @ 1.73Ghz. It came with 1.5GB (1 X 512mb 1 X 1Gb)that I later upgraded to duel 2gb sticks. It is only 32bit atm and pre SP1 Vista Ultimate (so it only sees 3gb) but with what I have, I disabled the swap file and run most everything just fine. Performance did increase a bit and my battery life went up about 30min or so when in power save mode with wireless on during my long late classes. I would think that having the harddrive shuffle less would definitly cause the battery to last a bit longer and well looks like my hunches were right.
anonymous x 04/30/2008 12:14 PM
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anonymous x
very nice, but i'll stick with 2 GB ram
Deleted profile 04/30/2008 1:13 AM
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"...at the German price comparison platform...." It is a AUSTRIAN platform. Let them be pride of something...
johnbilicki 04/30/2008 5:42 AM
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johnbilicki
Who in their right mind would leave virtual memory enabled? The most I've ever used is roughly 1.4GB in XP though Vista will cache things immediately after it's installed without knowing what I'll actually bother to use. This is just as bad as virtual memory!

I'll stick with XP and my 2GB of Corsair until a version of Linux that doesn't require you to wander in to the console every five minutes comes along.

...one nice thing though is that the reviews consider reasonably priced equipment. I don't care about 8800 Ultras, 9800GX2s, or thousand dollar CPUs. I've got more important priorities then trying to impress people who aren't getting any work done.
PhrexianGhoul 04/30/2008 8:09 AM
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PhrexianGhoul
This may seem like a silly question, but at the rate which SSHD's are gaining capacity and speed wouldn't that make DDR memory a thing of the past? At least i hope there will come a point in which read and write times to/from a SSHD would be as fast as the latest DDR2/3 memory and beyond. And if SSHD could achieve such speeds i think it would be completely possible to remove system memory and partition of a section of the HD to serve as the systems memory. And in the event that one could do this, one could easily adjust the memory as needed. The only limitation that i see would be in the operating systems ability to handle "x" amount of memory. Now this may not work at all, but it was a thought that had occurred to me while i was reading the article.
JPForums 04/30/2008 3:25 AM
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JPForums
Lets explore that thought shall we.
The fastest SSD I've seen has read/write speeds of approximately 110MBps/80MBps and an access latency of about 0.1ms.
If significantly faster SSDs are currently for sale, please forgive me for not keeping up with storage tech the way I used to. (BTW, FusionIO is neither an SSD nor affordable outside of datacenters)

To simplify things we'll just use the faster of the two.
110MBps = 880 Mbps
This is roughly the effective throughput of single channel DDR-400 on an AthlonXP chipset. (Memtest86(+))
It is a little more than half the effective throughput of the single channel DDR-400 controller on the socket 754 Athlon 64 systems.
It is less than a quarter of the effective throughput of the dual channel DDR2-800 controller on an Athlon64 X2.
I don't have readily available numbers on an Intel DDR3 system, but you can see where this is going.
(I could have put in Intel memory controller results and/or AthlonXP dual channel results, but these numbers fit better to get the general feel of things)

These results aren't bad actually.
SSDs may not have reached even the last generation of memory technology, but at least in throughput, they match RAM technology that was widely used to run Windows XP.

Side note: If you use theoretical bandwidth, then SSDs can't reach DDR-400 (3200Mbps) until the interface gets upgraded to 4GHz (~400MBps).
If the numbers seem funny to you, it's because I'm taking into account the 10/8 encoding scheme that SATA uses.

The real kicker is the access time.
0.1ms seems very fast in HDD terms, but on a 2GHz processor, this is about 200000 cycles of latency.
Compare that to:
150-165 cycles for the AthlonXPs
125-140 cycles for P4s
~60 cycles for Athlon64s

RAM is made to be accessed very often in relatively short bursts.
Until SSDs can get the latency down, they have no hope of replacing RAM.

If mass storage were as quick as RAM, you wouldn't dedicate part of it to be used as RAM.
Rather, you would manipulate the files directly from the mass storage device.
This would eliminate RAM all together, reducing overhead and potentially power consumption.
Unfortunately, no current mass storage device has the potential to do that.
I'm still waiting for MRAM to make its appearance.
It used to hold promise, but after waiting so long I lost interest and stopped keeping up with it.
Perhaps it can do what flash can not.
tphillips63 04/30/2008 3:30 AM
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tphillips63
That is good information but I would like to have seen 3GB numbers using a 2GB and a 1GB SODIMM.
notherdude 04/30/2008 11:16 AM
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notherdude
Well, if battery life goes up on a laptop that significantly would not power consumption on a desktop also improve? If so, this would be a noteworthy fact. I could easily see the extra ram paying for itself in energy savings not to mention helping the environment.
mmc4587 05/01/2008 7:33 AM
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mmc4587
If you wan't maximum battery with 2 or 3GB just turn off the swap-file.
windego 05/06/2008 8:22 AM
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windego
You could just turn off swap space. Then it wont use the harddrive, thus preserving battery life. I refuse to run vista, preferring Linux and xp in dual boot.

Feeding the OS endless amounts of ram is not a long term solution to an underlying performance issue. I can run Ubuntu linux with all the fancy compiz-fusion eye candy with just 512mb and it's smooth. Vista doesn't run smooth even with 1gb; it's a real dog. I understand why everyone is avoiding it like the plague, except of course those poor unfortunates who bought into the Direct X 10 marketing fallacy, and others who bought a new machine with it preinstalled (microsoft tax).
Christopher1 05/07/2008 9:20 AM
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Christopher1
Just make sure that once you put in that 4GB's of RAM, that you TOTALLY disable the swap file on the hard drive. I've done that for my notebook, and it gets nearly 3 times the battery life that it did after putting in 4GB's of memory and before disabling the swap file totally.

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