"supported" RAM configurations

Discussion in 'PC Hardware' started by Timothy Daniels, Aug 29, 2012.

  1. My Dell Precision T3500 64-bit workstation seems to have
    overly restrictive "supported memory configurations".
    The RAM that is installed now consists of (2) 2GB sticks of
    DDR3 1333MHz unbuffered ECC SDRAM. I would like to
    install (2) more sticks of 2GB each. But the RAM
    configurations "supported" by Dell, which are listed
    below in the following format, do not include this:


    1GB,1GB,1GB - 1GB
    1GB,1GB,1GB - 1GB,1GB,1GB

    2GB,2GB,2GB - 2GB,2GB,2GB

    4GB,4GB,4GB - 4GB,4GB,4GB

    Excluded are such configurations as:

    2GB,2GB,2GB - 2GB
    4GB,4GB,4GB - 4GB

    Is there any actual performance reason why the
    above 3 configurations are excluded? Or is it just
    that Dell hasn't tested them?

    Timothy Daniels, Aug 29, 2012
    1. Advertisements

  2. Timothy Daniels

    Yousuf Khan Guest

    I assume this uses some form of Xeon processor using triple-channel
    memory. And there are two separate banks of triple-channel memory too.

    So it's most happy when there are 3 sticks of memory in each bank, but
    it will support single- and dual-channel memory configurations in some
    limited capacity.

    It will only support single-channel memory if you're using 1GB RAM, but
    not higher. It will only support dual-channel memory if you're using 2GB
    RAM or lower, but not higher. It'll support triple-channel memory with
    all sizes of RAM.

    The second issue is the second bank of memory which seems to be less
    flexible than the first bank. Only with 1GB RAM can you have mixed
    triple-channel and single-channel banks. Mixed triple-channel and
    dual-channel are not supported at all. Even two banks of dual-channel
    are not supported at all, even though they are both similarly
    dual-channel. It looks like triple-channel is the native configuration,
    while anything less is being supported grudgingly.

    Yousuf Khan
    Yousuf Khan, Aug 30, 2012
    1. Advertisements

  3. Timothy Daniels

    Paul Guest

    I can't find an Intel reference on the subject. Strictly speaking,
    there should have been a section in one of the two i7 LGA1366 processor
    specs, but they don't seem to be putting memory details there like they
    should. Similarly, while in the past some of the chipsets had a
    "Memory Guide" document, I wasn't able to find such a thing
    in this case. There is a pretty crappy generic Intel web page,
    which attempts to cover all dual, triple, and quad channel processors
    on the same page, but it's too damn fluffy. It does address
    "Flex Memory", which is the ability for systems to use non-matched
    configurations, but the table below doesn't really reflect that.

    ("My kingdom for a good technical writer...")


    See section 2.4 "System Memory", here. This is an LGA1366 Xeon
    motherboard, taking ECC or non-ECC memory. It should have the
    same population rules as your motherboard. The memory controller
    is inside the processor, so the DIMMs connect directly to the
    processor. To a large extent, that makes the rules less of a
    motherboard issue. A BIOS is still needed to program the
    memory controller, but in some cases, even that code comes
    from Intel. *Note* - It's always possible for Dell to do
    whatever they feel like, so this cannot be evidence to overturn
    what Dell has written. It's just the Dell table and restrictions,
    don't make any sense. The design details of this motherboard,
    are more reasonable.


    I've seen motherboards with triple channel LGA1366 sockets, and four DIMM
    slots. With a different colored slot for A2, to show it's an unmatched
    (performance sucking) option. I don't really know why they did it, because
    it's just a dumb idea. What doesn't make sense, is if 4 DIMMs work, why
    doesn't 5 DIMMs work ? Flex memory should be able to handle it. And
    in this table, there's no single DIMM configuration showing, and that
    must be an omission. I would expect A1 by itself, and A1+A2 to be
    viable as well. But this is all the Asus manual shows. The Asus manual
    does say, that using A2, B2, C2 by themselves won't work, and that implies
    A1, A3, A5 by themselves would work. So I suspect this table deserves
    a few more lines.

    Section 2.4.1

    Dimm A2 Dimm A1 Dimm B2 Dimm B1 Dimm C2 Dimm C1
    2 DIMMs --- Populated --- Populated --- ---
    3 DIMMs --- Populated --- Populated --- Populated
    4 DIMMs Populated Populated --- Populated --- Populated
    6 DIMMs Populated Populated Populated Populated Populated Populated

    Section 2.4.2

    "You many install 1GB, 2Gb, and 4GB ECC or non-ECC, unbuffered DDR3 DIMMs
    into the DIMM sockets.

    You many install varying memory sizes in Channel A, Channel B, and
    Channel C. The system maps the total size of the lower-sized channel
    for the dual-channel or triple-channel configuration. Any excess memory
    from the higher-sized channel is then mapped for single-channel operation

    Maybe an argument could be made, that the last paragraph quoted, matches
    up with a four DIMM configuration. If you did a five DIMM configuration,
    you could end up with triple-channel, dual-channel, and single-channel
    behavior at the same time, which might be a bit harder to program, so
    they didn't bother supporting it.

    In any case, in terms of buying memory kits, I think you're well covered
    and should not have any complaints. If you read the chart before
    buying, you should be able to buy something without making a mistake.
    You should be able to do a group of (1GB+1GB+1GB) and (2GB+2GB+2GB)
    for example, and that should work in triple channel mode.

    As with all ECC capable systems, you should not mix ECC and non-ECC DIMMs.
    Generally the rule there, is to be consistent when installing DIMMs.
    They should all be non-ECC or all be ECC equipped when installed. Past
    experience is the "motherboard will beep", if the populated types don't
    match. An argument could be made, that from a hardware perspective, the
    rules could be made more liberal, but I doubt they bother putting
    the extra logic in the BIOS code for it, and they'll just "beep and stop"
    if the whole kit isn't the same flavor.

    Good luck,
    Paul, Aug 30, 2012

  4. The processor is a Xeon and the chipset is "Intel X58+ ICH10".
    There are 3 memory slots with white retainers interleaved with
    3 memory slots with black retainers.

    That is a good description of what Dell's service manual says is
    "supported". It appears from your statements that "supported"
    means "supported by the motherboard and the Intel chipset" and
    not "tested and proven by Dell to work". In other words, your
    answer to my question about the configurations not listed is that
    those configurations definitely would not work. Is that true?

    Timothy Daniels, Aug 30, 2012
  5. "Paul" replied:

    That would be excluded from the "supported memory configurations"
    in the service manual. Do you mean to say that such a configuration
    would work anyway?

    Timothy Daniels, Aug 30, 2012
  6. Timothy Daniels

    Paul Guest



    But, be aware, that the LGA1366 platforms, do have their issues with
    memory detection. There will be other LGA1366 motherboard models
    on this site as well, which you can review for memory compatibility
    experiences. Using the customer reviews on Newegg, for the older LGA1366
    platforms, is another way to data mine this issue.


    Basically, that guy had a working 24GB configuration, and after a memory
    failure, had problems getting the replacement parts to play nice. And
    in that case, you'd expect all the modules were the same size (6*4GB).

    Another LGA1366 (non-Xeon). Another working config that no longer
    works right.


    There's some BIOS setting that has a part in issues like that, but
    you'll have to chase that down yourself (could mean reading hundreds
    of postings etc). I can't remember if it was a VCore/Vdimm or other
    voltage setting, an overclock setting, a USB setting, but there
    was some BIOS setting that was contributing to memory detection
    problems. The other kind of problem, is occasionally an LGA1366
    processor isn't seated properly, but I don't think that's the only
    problem. Since the memory controller is on the processor, it means
    the three memory channels use contacts on the bottom of the processor.
    If any processor contacts don't touch, a RAM test in the BIOS will toss
    out a stick or channel. (While the BIOS uses SPD to detect DIMMs,
    the BIOS also has a "legacy fallback plan", that involves an old
    fashioned peek/poke method for detecting whether RAM is really there.
    If a stick isn't completely connected, it'll fail the legacy test.)

    So while it would be nice to say "Yes" above, I think you should
    be aware there are lots of reports of detection problems.
    And in the first example, things were running fine for a while,
    before trouble showed up. In other cases, you'll find users
    who can't get what should have worked in the slots, to work properly.

    The ability to mix sizes of RAM on a channel, has been around for
    at least ten years. So I'm not particularly concerned by mixing
    3x1GB with 3x2GB in the six slots. The declaration of Flex Memory
    capability on that memory controller, does lend a degree of freedom
    to how things work. Even if you did something dumb, as in

    Ch0 Ch1 Ch2

    1GB---2GB---2GB <--- three slots the same color
    2GB---1GB---1GB <--- three slots the same color

    that should still run in triple channel mode. Because all channels
    have the same total amount of RAM.

    If you run a four slot configuration, like

    Ch0 Ch1 Ch2

    1GB--- --- <--- three slots the same color
    2GB---1GB---1GB <--- three slots the same color

    the Flex Memory thing should still be able to match 1GB---1GB---1GB
    worth for triple channel mode. And then the upper half of the 2GB
    module and the separate 1GB module, give you a total 2GB memory space that
    runs in single channel mode. In such a case, the memory space runs
    at different speeds (lower 3GB addresses have a higher bandwidth than
    the high 2GB addresses).

    Paul, Aug 30, 2012
  7. "Paul" elaborated:
    Here's how I would like to expand my current bank of (2) 2GB modules:
    2GB,2GB,empty - empty,empty,empty

    2GB,2GB,2GB - empty,empty,empty

    2GB,2GB,2GB - 4GB,4GB,4GB or 4GB,4GB,4GB - 2GB,2GB,2GB

    That way, I could continue to use the 2GB modules. It appears that
    you would expect that the latter two configurations would work.
    Is that right? Is one preferable over the other?

    Timothy Daniels, Aug 30, 2012
  8. Timothy Daniels

    Paul Guest

    I see all of those as working configurations.

    We can never be 100% certain about any motherboard, when it comes
    to BIOS bugs. But from a hardware perspective, all of your options
    above should work.

    Paul, Aug 30, 2012
  9. "Paul" affirmed:

    Thanks for your informed opinion, Paul. I see easier paths for RAM
    expansion, now.

    Timothy Daniels, Aug 31, 2012
  10. I think it would be quite likely that it would not work.

    They seem to be supporting low memory configurations in arrangements
    other than properly filling the triple channels but nothing else. That
    probably means support was specifically added for those

    Note that even if they work they'll be slower than using sets of 3.
    Loren Pechtel, Aug 31, 2012
  11. Timothy Daniels

    Paul Guest

    You still have the option of "data mining" and searching for
    other stories of LGA1366 population. I consider the Asus manual
    to be as good a predictor of technical capabilities as any. It's
    just, with LGA1366, there are a disturbing number of cases of
    problems with RAM detection. And I recommend more research
    in that area (to see what BIOS setting is a dependency). I
    suspect a higher percentage of those problems, are non-hardware
    related (not a socket contact issue).

    Paul, Aug 31, 2012
  12. Timothy Daniels

    Yousuf Khan Guest

    I would say it's more likely that Dell has chosen not to program the
    firmware to support those lower configurations of memory. The memory
    controller is located inside the Xeon CPU not the chipset (chipset is
    not involved with the memory anymore), so the amount of flexibility you
    have in programming the memory controller might be pretty limited. You
    have to program microsecond timing delays, based on distances the RAM
    chips are physically from the CPU, so they probably prefer to keep the
    number of variables pretty low, to avoid firmware bugs. They likely took
    a conscious decision to not support single- or dual-channel
    configurations except for the cheapest types of RAM, where cost is
    likely more of a factor. In the higher-end, higher-capacity RAM
    configurations you are more likely to populate all 3 channels in both
    banks, since you're likely looking for the best performance.

    Yousuf Khan
    Yousuf Khan, Sep 1, 2012
  13. "Yousuf Khan" commented:
    Dell's "Pro Support" (i.e. 2nd tier support) did say that Dell doesn't tell
    the tech reps any more than what is in the service manual, but one did
    comment further via email:
    "Just because it isn't in our manual doesn't [tell] me that it will not work. But I will
    say that if you mix them like that you will run into issues with the system getting
    most likely blue screens and random lockups and wouldn't work as we would
    want it to."

    Since I got ECC RAM for reliability and consistency, I might as well go
    with 2GB,2GB,2GB - 2GB,2GB,2GB rather than 2GB,2GB,2GB - 4GB,4GB,4GB.
    I mean, 12GB of RAM should be sufficient even for a full-boat Visual Studio 2012
    running on 64-bit Win7 Business with an Express SQL Server. Er..., right?

    Timothy Daniels, Sep 1, 2012
  14. Timothy Daniels


    Aug 5, 2018
    Likes Received:
    Well, now 6 years later, I finally ungraded the RAM in my T3500. I bought 3 sticks
    of 4GB, and I shifted the 3 existing 2GB sticks up for a configuration of:
    4GB, 4GB, 4GB - 2GB, 2GB. 2GB which works fine and checks out with MemTest86.
    Explicitly, that is 4GB in each white-tabbed slot, and 2GB in each black-tabbed slot.

    Oddly, although other random arrangements also worked with all sticks being usable,
    2GB, 2GB. 2GB - 4GB, 4GB, 4GB did NOT work! The RAM size in the white-tabbed
    slots and the black-tabbed slots are NOT reversible.

    I used refurbished Hynix RAM sticks - the same brand that Dell originally supplied.
    They cost $27 apiece from StarMicroInc in Fremont, Calif, and I thrashed them for 8 hrs
    with MemTest86 without any errors, so now I'm ready to add in my new 500GB SSD.
    (I just hate to get rid of old things. :) )

    TimDaniels, Aug 5, 2018
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.