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I am running a legacy Windows XP 32-bit PC (not for internet use of course). It has 2x4GB RAM which operates in dual-channel mode.

Obviously Windows XP can only use 4GB RAM. One could argue the second stick of RAM is pointless, but without it you only get single-channel performance.

Question: Even though Windows XP only uses 4GB RAM max, will I still enjoy dual-channel performance by having both sticks installed?

I'd benchmark this myself but I'd rather not tinker with the PC as it doesn't belong to me.

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  • Not every XP only supports 4GB. XP 64bit supports 128GB. en.wikipedia.org/wiki/Windows_XP_Professional_x64_Edition
    – barlop
    Commented Apr 19, 2015 at 10:23
  • A great question is how would you know, if it's using dual channel or not. I don't know but you could load up Si Sandra (or an equivalent program) and see what capacities it shows for both banks, it'd be interesting, it'll show you a result quickly, which may or may not answer your test. But see, foes it state there are 2GB on each bank or 4GB on one bank. Or 4GB on both banks. If it says 2GB on each bank then it'd be dual channel.. If it says 4GB on one bank then maybe quite likely that it's single channel but who knows.
    – barlop
    Commented Apr 19, 2015 at 10:26
  • If si sandra says 4GB on both banks then it isn't giving you any hints either way. But that's a test you could do.. I hope there is a better test that can be done. But no problem at all putting Si Sandra on somebody elses computer. It's not benchmark software.. no stress tests.
    – barlop
    Commented Apr 19, 2015 at 10:29
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    You've GOT to be kidding. This question... off-topic? Seriously? There's nothing in my question that asks for shopping recommendations. It's a technical question about dual-channel memory utilisation in a 32-bit OS which in this case is Win XP.
    – misha256
    Commented Apr 21, 2015 at 2:33
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    Come on people, this is not, in any way, a shopping question.
    – fixer1234
    Commented Apr 21, 2015 at 3:08

3 Answers 3

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Yes, your assumptions are correct. Windows XP 32bit will only be able to access 4GB (which is half your total), but the mainboard won't care about this limitation (assuming it supports up to 8GB or more).

The abstraction on how the memory is addressed or used happens (as far as I know) on the hardware level. As such it won't matter that Windows XP 32bit isn't capable of addressing everything. The board should still split all requests on both banks.

Just keep in mind that Windows XP's support period is over, do consider upgrading, which should be a bigger concern than some "wasted" memory.

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  • You write "XP will only be able to access half the memory" <-- He didn't contradict that. He may be asking if it's possible that the system will use 2GB from one RAM stick and 2GB from the other RAM stick and if it'd be dual channel that way. I'd think (as you perhaps are saying), probably not.
    – barlop
    Commented Apr 18, 2015 at 6:53
  • @Mario I get that XP will only see 4GB, but will that 4GB still operate in dual-channel mode? Technically, under the hood, that would require the memory controller to utilise both sticks of RAM. I'm not sure how OS agnostic a memory controller is...
    – misha256
    Commented Apr 18, 2015 at 7:45
  • @barlop IMO dual channel handling will happen on the hardware level. As such the operating system doesn't have to be aware of the feature. So, yes, it should use dual channel strategy, essentially with 2GB each stick.
    – Mario
    Commented Apr 18, 2015 at 15:47
  • @Mario in which case A)You are extremely unclear, your "answer" does not state whether he will or will not get dual channel. and I read it as he won't, your answer has the illusion of clarity by stating his assumptions are correct, but it doesn't actually answer his question clearly. He didn't assume one way or the other re dual channel being supported or not. B)And in your comment, you clarify, but then all you have to say is in your opinion, and not any reasonable evidence one way or the other to even support why your opinion is that way.
    – barlop
    Commented Apr 18, 2015 at 22:16
  • @barlop Him, yeah, rewording.
    – Mario
    Commented Apr 19, 2015 at 6:09
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Let me reply piecemeal:

  1. I am running a legacy Windows XP 32-bit PC (not for internet use of course). It has 2x4GB RAM which operates in dual-channel mode.

How do you know it runs DC without CPU-Z or other diag? No tool reports 8GB DC on WinXP32.

  1. Obviously Windows XP can only use 4GB RAM. One could argue the second stick of RAM is pointless, but without it you only get single-channel performance.

WinXP32 reports approx. 3.49GB with SP3 PAE patches. Yet I use 8GB (2x4GB) with a free RAMdisk tool to pool OS-invisible RAM for Virtual Memory (volatile) & Browser Cache (imaged at bootup & shutdown). So my matched sticks are utilized in DC although that blank field is grayed out on CPU-Z.

  1. Question: Even though Windows XP only uses 4GB RAM max, will I still enjoy dual-channel performance by having both sticks installed?

Matched sticks on a mobo with DC memory controller retain the capability irrespective of OS. But without bank-level interleaving optimal DC utilization is lost on WinXP32 unless you use a program to recoup the 'lost' memory like me.

  1. I'd benchmark this myself but I'd rather not tinker with the PC as it doesn't belong to me.

Factors like timing & rank may impact your DC 'benchmark'. If the PC is not yours why worry about it?

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  • If the PC is not yours why worry about it? Because maybe he or she is one of the primary users of that machine? I am the primary user on lots of machines that aren't mine, and I would be ticked off if I was having performance issues with them.
    – InterLinked
    Commented Mar 9, 2017 at 14:12
  • These advanced tricks require admin & hardware privileges. It is not considered professional in most fields of work to try them on work PC's. I would just call the help desk; the rest is your judgement.
    – Bunty
    Commented Mar 26, 2017 at 18:38
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I'm just adding an answer to compliment Mario's answer and all the various comments.

In all Intel's documentation an OS requirement is never mentioned in relation to enabling multi-channel memory. Here's an example.

In the above example, the benchmarks Intel ran were on a Windows XP 32-bit configuration.

Additionally, there are certain editions of 32-bit Windows support PAE which allows access to more than 4GB RAM. Even Windows XP supports PAE, although it was disabled as of SP2 (but can be hacked to be re-enabled).

I know it's not 100% conclusive evidence, but it gives me enough certainty that dual-channel performance is realised regardless of what operating system you choose to run. I would love to benchmark MS-DOS to prove this beyond doubt... might do that at some stage ;-)

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  • PAE is a requirement for supporting more than 4 GiB of RAM on x86, but you can have it enabled without accessing more RAM. It’s required for NX, for example. That’s why it was almost certainly never removed.
    – Daniel B
    Commented Apr 22, 2015 at 6:34
  • Correct, XP SP2 does not "disable" PAE. It does prevent the OS from using RAM that's at physical addresses above 0xFFFFFFFF (the 4 GiB point). Nevertheless PAE is still enabled, as it's required for hardware DEP /NX.
    – Jamie Hanrahan
    Commented Feb 22, 2017 at 17:01

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