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  1. #1
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    'Inaccessible boot drive' error blocks startup


    LangaList Plus

    'Inaccessible boot drive' error blocks startup


    By Fred Langa

    When something goes seriously wrong with the Windows boot process, there are several tools and options you can use to return full access to your system. Here's what to do.

    Plus: Thousands of photos are mysteriously altered to a lower resolution, and why a 64-bit system might be limited to 4GB of RAM.

    The full text of this column is posted at windowssecrets.com/langalist-plus/inaccessible-boot-drive-error-blocks-startup/ (opens in a new window/tab).

    Columnists typically cannot reply to comments here, but do incorporate the best tips into future columns.

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    Lounger Will Fastie's Avatar
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    Regarding RAM limitations, it is also the case that the processor itself limits the total RAM, although it's been a long time since I've seen a 4GB limitation. A good place to check that is http://ark.intel.com/.

    And you're right about mainboard limits. I have an older PC with a Core 2 Duo processor, which supports up to 16GB of RAM. The PC, however, supports just 4GB and there is no way to alter than via the provided BIOS.

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    Quote Originally Posted by Tracey Capen View Post

    LangaList Plus

    Plus: ... why a 64-bit system might be limited to 4GB of RAM.
    Unless I overlooked it, you missed the biggest reason: Windows (or any other Operating System) must be 64-bit. A 32-bit OS will address a maximum of 4 GB, and actual memory can be drastically lower, sometimes well under 3 GB, depending on how much is used by memory-mapped I/O devices -- video is usually memory-mapped.

    --Scott.

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    3 Star Lounger
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    re. "Why is this 64-bit system limited to 4GB of RAM?"

    Go to crucial.com, download and run their "Crucial System Scanner". It will tell you what memory upgrades Crucial can offer for your system.

    And the nice part is they guarantee every upgrade they recommended and you bought from them.

    Their prices are competitive in my experience.

    Generally: For every higher power of 2 in memory space that a motherboard can address one additional bit is required in the addressing logic and thus in the physical address lines on/in the board. That has consequences for the price. And the rest is history as they say...
    Eike J Heinze
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    Innaccessible Boot Drive Error Blocks Startup

    Hi,
    I experienced exactly the same problem recently, which took a few hours of searching to figure out, but then just a few minutes to resolve.
    I was also using Acronis True Image, and suddenly found I was unable to load the operating system.
    To cut a long story short, it appears that True Image had changed the MBR.
    I used the Windows Recovery Environment to access the command prompt to rebuild the MBR, using the following command -

    Bootrec /fixMbr

    This took literally a few seconds to run, and immediately solved the problem - all has been fine since.
    I hope this helps.
    Thanks

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    Super Moderator satrow's Avatar
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    Different Windows SKU's also have licensing limits on the memory that can be used, the details for Windows 7:

    Version Limit on X86 Limit on X64
    W 7 Ultimate 4 GB 192 GB
    W 7 Enterprise 4 GB 192 GB
    W 7 Professional 4 GB 192 GB
    W 7 Home Prem.4 GB 16 GB
    W 7 Home Basic 4 GB 8 GB
    W 7 Starter 2 GB N/A
    Note that MS have (again!) used the term "Physical Memory" here, which is obviously incorrect: Memory Limits for Windows and Windows Server Releases

    The original article that called MS out on this deception/error: Licensed Memory in 32-Bit Windows Vista

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    A minor correction to my note: Some 32-bit CPUs, mostly server CPUs, support an extended number of address lines, so that a 32-bit OS which supports it can work with more than 4 GB of physical memory. In fact, the mechanism behind this is the same mechanism which explains the large memory in 32-bit Windows (especially on 64-bit hardware) in the article linked by satrow (which I read AFTER writing most of this reply). Also, I seem to recall a few systems were designed to swap between RAM and memory-mapped I/O, cutting down on unusable physical memory.

    Apps are generally limited to the same physical memory as the OS. And, yes, apps also come in 32-bit and 64-bit versions; a 32-bit app would generally be limited to 4GB of data in memory, even under a 64-bit OS, although that depends upon programmer assumptions and how the memory is allocated.

    Will Fastie mentions CPU limitations; as far as I know, no modern CPU, chipset, or motherboard is actually capable of coming anywhere near to handling the full amount of RAM which could theoretically be addressed by a 64-bit CPU, so all current 64-bit CPUs are restricted, and are likely to be for many years, unless someone invents something revolutionary.

    --Scott.

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    Quote Originally Posted by satrow View Post
    Note that MS have (again!) used the term "Physical Memory" here, which is obviously incorrect: Memory Limits for Windows and Windows Server Releases
    Why is physical incorrect? Aren't they distinguishing from virtual memory in a paging file on disk?

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    Quote Originally Posted by BruceR View Post
    Why is physical incorrect? Aren't they distinguishing from virtual memory in a paging file on disk?
    It might be better to say something like "Adjusted physical memory", or "licensed physical memory".

    --Scott.

  11. #10
    Super Moderator satrow's Avatar
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    Quote Originally Posted by BruceR View Post
    Why is physical incorrect? Aren't they distinguishing from virtual memory in a paging file on disk?
    RAM only is referred to there, maximum RAM is limited by SKU licence, not by any physical restriction, even if you fitted more RAM that the BIOS recognises, Windows wouldn't use it.

  12. #11
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    Also, the motherboards have limits as to how much memory they may support. You will need to consult the specifications for the motherboard to determine the maximum amount of memory your motherboard may support. Both Crucial and Kingston websites also show this value.

  13. #12
    Super Moderator satrow's Avatar
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    Since this issue has raised it's ugly head once more, I'll tempt you all with a few more snippets, please dig into the 'original'* articles for the finer details, don't neglect the extant* comments on the Russinovich article.

    Russinovich:

    Windows Server Memory Limits

    Windows support for physical memory is dictated by hardware limitations, licensing, operating system data structures, and driver compatibility. The Memory Limits for Windows Releases page in MSDN documents the limits for different Windows versions, and within a version, by SKU.

    You can see physical memory support licensing differentiation across the server SKUs for all versions of Windows. For example, the 32-bit version of Windows Server 2008 Standard supports only 4GB, while the 32-bit Windows Server 2008 Datacenter supports 64GB.
    However, by the time Windows XP SP2 was under development, client systems with more than 4GB were foreseeable, so the Windows team started broadly testing Windows XP on systems with more than 4GB of memory. Windows XP SP2 also enabled Physical Address Extensions (PAE) support by default on hardware that implements no-execute memory because its required for Data Execution Prevention (DEP), but that also enables support for more than 4GB of memory.

    What they found was that many of the systems would crash, hang, or become unbootable because some device drivers, commonly those for video and audio devices that are found typically on clients but not servers, were not programmed to expect physical addresses larger than 4GB. As a result, the drivers truncated such addresses, resulting in memory corruptions and corruption side effects. Server systems commonly have more generic devices and with simpler and more stable drivers, and therefore hadn’t generally surfaced these problems. The problematic client driver ecosystem led to the decision for client SKUs to ignore physical memory that resides above 4GB, even though they can theoretically address it.


    Chappell:

    That 32-bit editions of Windows starting with Windows Vista are limited to 4GB is not because of any technical constraint on 32-bit operating systems. The 32-bit editions of Windows Vista and Windows 7 all contain code for using physical memory above 4GB. Microsoft just doesn’t license you to use that code.
    A Marketing Ruse

    Perhaps the following, from Pushing the Limits of Windows: Physical Memory by Mark Russinovich at a Microsoft website, ends with a more frank description of Microsoft’s thinking about this 4GB limit than can be found in anything written directly by Microsoft:

    "Because device vendors now have to submit both 32-bit and 64-bit drivers to Microsoft's Windows Hardware Quality Laboratories (WHQL) to obtain a driver signing certificate, the majority of device drivers today can probably handle physical addresses above the 4GB line. However, 32-bit Windows will continue to ignore memory above it because there is still some difficult to measure risk, and OEMs are (or at least should be) moving to 64-bit Windows where it's not an issue."


    I've added some bold to enable the skimmers and tech authors/columnists amongst you to pick out a few pointers.

    *Note that the text of the Russinovich article has modified, possibly several times, for various reasons. Older comments also appear to have gone AWOL.

  14. #13
    WS Lounge VIP Browni's Avatar
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    @satrow

    The 1st link isn't working.

    Is the spamfest from earlier being culled?

  15. #14
    Super Moderator satrow's Avatar
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    Working now, had been removed temporarily. Hoping the flood gates have been bolted shut and that they'll be a mere trickle in the future.

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