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RAM Memory Address Mapping

    Question

  • Before responding, please read the question carefully. It is not what you think. I know the "32 Bit OS, 4GB RAM" thing has been beatin to death. This however has never been brought up before. I've put at least 20-30 hours of research and Googling into this question, with no luck.

    [Example Setup]
    [Windows 32 Bit Operating System]
    [Two Memory Sticks Installed, at 2GB Each, for 4GB Total]

    We already know, that only about 3.2GB or so of your RAM will be mapped in the address.

    However, my question is in regards to Dual-Channel Memory.

    *Will the system map each individual memory module equally?*

    Explanation: Will the 3.2GB of addressable memory be split between each stick, so that 1.6GB on each stick gets mapped equally, with each stick having 400MB of leftover unmapped memory?

    Why do I ask this?

    Because it's important to the proper functioning of RAM, especially in Dual-Channel.

    Think about this, since only 3.2GB or so is addressable, its possible that the first 2GB will go entirely to Stick #1, and Stick #2 will only get a 1.2GB address.

    So with Dual-Channel memory, you could potentially experience a Crash or BSOD or something similar when a program exceeds 2.4GB of RAM usage, because now Stick #1 is able to continue filling up with ram, but Stick #2 has reached it's limit, so a crash occurs.

    Also, one of the sticks would receive extra usage over the other, resulting in reduced life expectancy.

    I truly appreciate the effort of everyone's response.

    Saturday, February 09, 2013 8:08 AM

All replies

  • Dual channel memory has no relationship to memory mapping as you ask about above.

    See article @ http://en.wikipedia.org/wiki/Multi-channel_memory_architecture

    Multi-channel memory architecture is a technology that increases the transfer speed of data between the DRAM and the memory controller by adding more channels of communication between them. Theoretically this multiplies the data rate by exactly the number of channels present.
    Dual-channel memory employs two channels which theoretically doubles the data transfer rate.

    Dual-channel architecture

    Dual-channel-enabled memory controllers in a PC system architecture utilize two 64-bit data channels. Dual channel should not be confused with double data rate (DDR), in which data exchange happens twice per DRAM clock. The two technologies are independent of each other and many motherboards use both, by using DDR memory in a dual-channel configuration.

    Also found @ http://www.crucial.com/kb/answer.aspx?qid=3751:

    What is dual-channel memory?

    The terminology "dual-channel memory" is being misused by some in the memory industry, which can mislead the consumer. The fact is there's no such thing as dual-channel memory. There are, however, dual-channel platforms.

    When properly used, the term "dual channel" refers to the DDR or DDR2 chipset on certain motherboards designed with two memory channels instead of one. The two channels handle memory-processing more efficiently by utilizing the theoretical bandwidth of the two modules, thus reducing system latencies, the timing delays that inherently occur with one memory module. For example, one controller reads and writes data while the second controller prepares for the next access, hence, eliminating the reset and setup delays that occur before one memory module can begin the read/write process all over again. Think of it like
    two relay runners. The first runner runs one leg while the second runner sets up and prepares to receive the baton smoothly and carry on the task at hand without delay. While performance gains from dual-channel chipsets aren't huge, they can increase bandwidth by as much as 10 percent. To those seeking to push the performance envelope, that 10 percent can be very important.

    If you have a dual-channel platform and you want to take advantage of the performance gain it offers, our advice is to simply purchase your DDR or DDR2 memory in pairs. However, be very careful to order two modules with the exact same specifications; the modules must be identical to each other to perform correctly.


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    • Edited by Rick Dee Saturday, February 09, 2013 12:41 PM
    Saturday, February 09, 2013 12:38 PM
  • Okay, that is good information about Dual Channel.

    But what about the Memory Addressing part of it. Ignoring the Dual-Channel side of things, if you have multiple (Sticks) of ram in a system that has limited memory mapping available. How does it address those sticks? Equally, or in order of priority?

    Referencing my original post, with 2 sticks installed, does Dimm 1 get 2gb mapped, while Dimm 2 gets the leftover 1.2gb? or do they get equally addressed?

    To be honest I'm surprised this hasn't come up before, because a ton of systems out there, are in this configuration. Many users have more RAM installed in their system, than their operating system can address. Especially since all versions of windows have different restrictions for RAM. Windows 7 64-bit for example, you must buy the "Premium" edition to get access to the 128GB of RAM mapping, whereas the several editions below it, allow only 4 to 16 GB even though it's a 64-bit system. Which many people don't realize... hence the millions of "Why does my system only show xxx RAM Installed" questions posted all over the internet. And of course, it's even worse for 32-bit systems, especially in todays age, where RAM is now soo cheap in price, that you can easily max out the latest operating systems (including 64-bit), unless you purchase the specific (and more expensive) editions which allow the full 128GB.

    All of that aside though. The question is still important, even without the Dual-Channel part of the equation, because Stability is still a major concern, especially for those of us that build our own systems, gamers, and overclockers.

    Sunday, February 10, 2013 6:23 AM
  • Seems like Dual Channel still applies to this question though:

    http://www.intel.com/support/motherboards/desktop/sb/cs-011965.htm

    According to Intel, Dual Channel, Triple Channel, and Quad Channel Memory runs in "Interleaved" mode which means it reads and writes equally between each memory module, instead of just filling up one stick then moving onto the next, as seen in "Assymetric" or "Single" or "Flex" modes which occur when one stick is installed, or multiple sticks of different sizes/speeds, or if sticks are installed in the incorrect DIMM slots.

    Sunday, February 10, 2013 7:08 AM
  • You need to go back to your reference and re-read it very carefully.  There is absolutely no mention of "memory mapping" in the article.

    If you read the article and comprehend what it is saying, it is referring to access speed, or processing speed, and not mapping!


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    Sunday, February 10, 2013 12:30 PM
  • There is no relationship between "memory mapping" and dual channel memory.

    All the articles plainly state multi-channel memory enhances the access speed, or processing speed.  It has nothing at all to do with "mapping" of the memory. 


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    Sunday, February 10, 2013 12:34 PM
  • If you really want to be confused, look up "ganged memory" and try to relate that to memory mapping.

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    Sunday, February 10, 2013 12:54 PM
  • I understand.

    I'm not really concerned about Dual Channel though.

    What I want to know, is if your RAM Modules. The physical sticks are addressed equally, or if it addressed in order by DIMM slot.

    In all of the 32-bit 4GB Memory, posts about, "Where is my 4GB of memory, how come it only shows 3.25GB" etc etc. The answer is because every component in your system must be addressed by the system, and each of those components uses a small amount of space in the address, thus reducing the amount that is left for RAM, because RAM is the last component in this system of prioritization.

    So. With that in mind.

    When the address finally gets down to your RAM Sticks...

    Does it address all of Stick 1... then move onto Stick 2... Or does it treat them equally, and address them both the same.

    In 32 Bit windows you only have a 4GB block to work with. So from my original post/example, would Stick 1 have all 2,048 MB of it's memory addressed, thus leaving only 1152 MB addressed in module #2.... or will they both get 1600 MB addressed equally between them.

    The whole "Dual-Channel" part of the question was just thrown out there as some that could "Possibly" be affected by this. So even if it is now taken out of the equation, as you have said... My original question still remains.

    This discussion is about Memory Addressing in a 32 bit windows system. In relation to the 4GB Limit.

    Monday, February 11, 2013 8:15 AM
  • You will have to get the answers for your questions directly from the hardware designer of the motherboard.  Windows sees a matrix of memory locations.  How the memory is addressed is a function of the motherboard designed as determined by the engineers that design the board, how the components are connected, how the memory matrix is built, and exactly where to run the foil for the electrical connections.

    Windows does not care how the memory matrix is configured by the hardware.


    Please remember to click “Mark as Answer” on the post that helps you, and to click “Unmark as Answer” if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread. ”

    Monday, February 11, 2013 11:21 AM