Laptops 1 GB + 512 MB dual channel - How ??

Brendon

Brendon

Forerunner
Could someone please explain to me how this weird combo is working in dual channel mode. I thought modules had to be identical.

 
because two of your 512mb are placed in slot 1 and 3 .. na its obvious dual channel can't run without two identical modules. so everest must be referring to these two 512mb and not the whole memory system

edit: I could be wrong heh
 
This is a laptop ! It has only 2 memory slots. I have a 512 MB stick in 1 slot and another 1 GB stick in the other !

Even CPU-Z and Sisoft Sandra 2007 confirms this !
 
1GB will run in dual channel mode (512+512) and the rest of the memory (512MB) will be used in single channel mode. It's been like this since the AXP days and the first dual channel memory controller.

Matched module requirements are hardware limitations of chipsets and memory modules. We've seen Dual channel run fine on non-identical modules before, as long as the stick is able to operate within the settings of the board it works (determined by the cheaper/lower quality module). Memory controllers are driven by software, and don't need identical modules, which is why this scheme works at all.
 
IGN: Asus A7N8X Deluxe nForce2 Review

Dated the beginning of 2003. It's somewhere in that review. The reviewer is indeed correct that dual channel does not require equal amounts of memory in both channels to operate.

This is not an Intel exclusive/feature, the board in review is a nForce2 board for the Athlon XP.

Edit: In case it is not clear, I'm referring to post no. 5's suggestion that this is available on Intel chipsets only.
 
That's a brand name. We're talking about functionality. Functionally, dual channel has never required equal amounts of memory. You could call it 'flex' or 'neo' memory or any such thing, but this has been the truth since the nForce2 SPP. And then, the memory controller was very much in the SPP, not the chip.

Flex is probably a reference to the fact that Intel chipsets are now flexible enough to accept different size sticks as opposed to the RAMBUS days where you had to precisely match the two channels. That was also the origin of 'dual channel' memory kits, and Flex memory is maybe Intel's announcement that their chipsets do not need this now.

Physical location of the memory controller does not affect its functionality. The discussion you've looked up is incorrect in the statement that AMD/compatible memory controllers does need equal memory amounts in the channels. They do not. Here's a slightly more technical explanation.

nForce2: single-channel mode vs. dual-channel mode

What's needed for the dual-channel mode of the nForce/2? At least, two memory modules, with one installed exactly into the DIMM0 slot which is arranged differently than DIMM1/2 or DIMM1, with the DIMM2/3 being provided as well. In case of wrong installation the second memory controller might not operate. The modules can be different (as well as their producers), but their speed characteristics should be the same, otherwise the system will operate at the speed of the slower one (for example, DDR266 in case of one DDR266 and one DDR400 modules). It's also possible to use three modules, but remember that the dual-channel access can be set only for the memory size equal to the double size of the first module (which is installed into the slot of the lowest number), and if the size of the first module does not exceed the sum of the sizes of the second and third modules. Obviously, there are two most optimal cases: equal memory modules inserted into the first and second slots, or three modules, with the first one being equal to the sum of the other two modules.
Click to expand...

Note the use of the word optimal - not essential.

And here's the nVidia whitepaper. Point no. 2 on page no. 7, clearly says

Both controllers are functionally identical with all control and timing parameters independently programmable. This allows asymmetric DIMMs with different memory organization, size, and speed to be used on MC1 and MC2 and still provide the full performance benefits of the 128-bit memory system
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http://www.nvidia.com/object/LO_20010528_5545.html

Edit: Just to know that this feature also existed on X2 processors (I can't find a reference for the Venice core Dual-channel controller but rest assured it was there too - you can't restrict a user to only configure their system one way!) here's a final link.

Athlon 64 X2 processors are based on the Toledo and Manchester cores with E stepping, i.e. their functionality is similar to that of the Athlon 64 processors on San Diego and Venice cores (except for the ability to process two computational threads simultaneously). Athlon 64 X2 also supports SSE3 instructions and features an enhanced memory controller. Among the peculiarities of the memory controller of the new Athlon 64 X2 I would like to mention the support of different memory DIMMs in different channels (it even allows installing memory modules of different capacity in different channels) and the support of up to four double-sided DIMMs in DDR400 mode.
Click to expand...

X-bit labs - AMD Athlon 64 X2 4800+ Dual-Core Processor Review (page 2)

Last but one paragraph.
 
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