hardware reserved memory?

Discussion in 'Memory' started by Bigbacon, Feb 20, 2019.

  1. Bigbacon

    Bigbacon [H]ardForum Junkie

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    Never noticed this before. is this a windows 10 thing or something else?

    I have 32gb of ram total but windows says 31.9 and that 51.9MB of ram is hardware reserved?

    Obviously nothing to worry about but curious why that might be?

    MSI x470 motherboard, ryzen 2700x, 1080 TI.
     
  2. KonaKona040

    KonaKona040 n00b

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    I've seen hardware reserved memory for IGP before, but you don't have an IGP in that setup...

    Have you dug around in your bios?
     
  3. SvenBent

    SvenBent 2[H]4U

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    i can't explain all of it but i know windowsNT always blocked out the first 1meg+ 64kb of ram since windows NT4

    This is to avoid data corruption from bad E820 maps from the bios (shadowing etc etc)
    This was also common issues for memtes86(+) and why later edition did the same. simply ignoring the first 1meg+64kb


    Why 1meg+64kb you say

    well back in the 386day or so memmory adress was done in segments. of 16bit adreses
    the cpu coudl adress 1meg of ram and anything above that had to be handeld with "paioging in and out ofr the ueseable memmory and the expanded memmory

    below the 1meg line we had
    640kb of conventialn memmory ( forrunning programs_
    386 of ubber memory ( for biosshadowing and later also for driver and eMS/XMS memmory manager etc)
    anything above 1meg was suppoed to be expanded memmry

    But then somebody realised that the double 16bit segment adressing scheme could cover a bit above 1meg. an exatly 64kbytes more mmory
    this area was name high memmory and just like upper memmory could be used to offload some of the stuff to free up upper and/or conventionel memory


    What is the issues then you might ask?
    Well the issue is the bios is suppoed to hand over a memmory map cal E820 to inform the memory manager which ares was used for shadowing and thereby reserved.
    but after dos kinda died out the bios programm got lazy and this memmory map was often wrong. ( asus was especially was bad on this).
    so if you memmory manager was inform and area was free but it was in fact used by the bios for shadowing. the smemmroy are would be filled with teh bios info. and as a sefety mechanism the bios would write protect that area.
    you memmory manger now might try to write to this area and it would do so fine.
    But once it would read it back the wanted data would not be there. instead some bios data would be read and you would have data corruption and unstability

    So to protect the OS against bad bios implemantations windows do not use the first 1meg+64kb of ram

    you can try palying around with this by using older version of memtest that relies on the E820 map and you will se on some computer you will get tons of data errors in these locations
     
    Last edited: Feb 20, 2019
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  4. Bigbacon

    Bigbacon [H]ardForum Junkie

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    only bios change I made was to choose the right memory AMP/XMP whatever config.
     
  5. asheron42

    asheron42 n00b

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    The memory is reserved by your motherboard for devices.

    So memory can be hardware reserved if: it can't be addressed (limitation by OS/bios/bad module) or is being shared by a h/w device.

    50ish MB is about normal for a motherboard, it handles the controller cards like sound/raid/ethernet anything that doesn't have built in memory and needs to share. Sometimes you'll see around 500MB, which is onboard video.
     
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