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Huge amount of RAM reserved for hardware? RRS feed

  • Question

  • Hello,

    our WES7-Image (x86/32bit) is used for a couple of different hardware platforms, on of them is based on Intel's 6th generation CPUs (a.k.a. Skylake).

    We noticed that about 1800MB of RAM are reserved for hardware on the Skylake system (as per Resource Monitor), this is almost three times more than older system, where about 700MB are reserved for hardware. We can reduce this by changing the BIOS setting "TOLUD" to another value than dynamic, f.ex. to 3.5GB - the rsult is that about 700MB of RAM becomes available. Better than the initial situation, but still much more than on older systems.

    After some analysis I found out that most of the resources are assigned to a device called "PCI Bus", where it's address range covers the address ranges of several PCI devices (SATA controller, Ethernet controllers,...). If I set the BIOS settings to dynamic, about 1.28GiB are assigned to "PCI Bus", and about 512MiB if I set it to "3.5G" (which is the highest possible setting). However, when I add up all memory ranges that falls within the range of "PCI Bus", I count about 235MiB which are designed to these devices. With other words: regardless of the setting - at least 250MiB are still avialable for any hardware - IMO, that is much enough for an embedded system since customer has no abilitiese to add additional PCI(e) hardware.

    On the other hand: When I installed Win10 IoT (64bit) to the same hardware, only a view MBs of memory are assigned to hardware... In summary: It seems that it depends on O/S as well as on HW how many RAM is reserved for hardware??

    Can anybody explain why the same O/S reserves different amount of RAM when it runs on different HW, or why differnt O/S reserve different amount of RAM on the same HW? Does anybody know some background about who decides how many RAM should be reserved for HW, and why?

    At least following question remains: Do you think it's critical to set the BIOS setting "TOLUD" to 3.5G by meanings of having about 250MiB of RAM left for hardware? As mentoined above, the only devices that custumers may add must be attached to one of the four USB ports.

    Have much thanks in before.

    Willi K.

    Tuesday, October 30, 2018 1:50 PM

Answers

  • A couple of time has passed, but did not get more useful information about who decides the amount of RAM that is reserved for hardware. Mainboard vendors told us that this is implemented somewhere in the BIOS (or UEFI firmware), this in turn is assumed to be done because of Intel's specs and so on.

    The only thing that you can do is trying to find a good value for the TOLUD setting in the BIOS settings. But handle with care: Our mainboard vendor told us that HW may not work properly if TOLUD is set to high...

    • Marked as answer by Willi K Tuesday, December 11, 2018 1:50 PM
    Tuesday, December 11, 2018 1:50 PM

All replies

  • Willi with Intel boards some of the RAM is being used by the Video Controller.

    I suggest that you also post to the https://social.msdn.microsoft.com/Forums/en-US/home?forum=HardwareBoards&filter=alllanguages forum as there are hardware device driver folks that might be able to answer the question more clearly,


    Sean Liming - Book Author: Starter Guide Windows 10 IoT Enterprise - www.annabooks.com / www.seanliming.com

    Tuesday, October 30, 2018 3:10 PM
    Moderator
  • Sean,

    you're right - a portion of the memory is assigned to the graphics controller. We can modify this in BIOS. Regarding the rest I followed you suggestion and posted the question to suggested forum.

    Thanks.

    Willi K.

    Tuesday, October 30, 2018 4:02 PM
  • A couple of time has passed, but did not get more useful information about who decides the amount of RAM that is reserved for hardware. Mainboard vendors told us that this is implemented somewhere in the BIOS (or UEFI firmware), this in turn is assumed to be done because of Intel's specs and so on.

    The only thing that you can do is trying to find a good value for the TOLUD setting in the BIOS settings. But handle with care: Our mainboard vendor told us that HW may not work properly if TOLUD is set to high...

    • Marked as answer by Willi K Tuesday, December 11, 2018 1:50 PM
    Tuesday, December 11, 2018 1:50 PM