- Vista Workshop: More RAM, More Speed
- High-End DDR3 Memory on the Hook
- DDR3-1333 Speed and Latency Shootout
- PC Memory: Just the Facts
- The New Arms Race: DDR3-1800 RAM
- Hardcore DDR2 RAM by Corsair, G.Skill, OCZ and Patriot
- Overclocking 9 Value-Priced DDR2-800 Kits
- Corsair's PC10000 Super-Ober-Uber-RAM Sets Sails
- Corsair's XMS2 Dominator: The World's Fastest DDR2?
- Live Memory Test: Overclock 'Em Till They Crash
Synchronous vs. asynchronous Dual Channel
Source: Tom's Hardware – Keywords: ram, scaling, notebook
Syndication:
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
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.
Dell utilizes a GM965 chipset (Santa Rosa) for its Latitude D630.
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.
- Previous page Some Memory Basics
- Next page Upgrading the Latitude D630



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.
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.
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).