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Discussion in 'Dell' started by Deodiaus, Jul 29, 2009.

  1. Deodiaus

    BillW50 Guest

    In Ben Myers typed on Tue, 11 Aug 2009 18:49:11 -0400:
    EFI partitions are FAT partitions with data and don't often have drive
    letters under Windows. Linux doesn't use drive letters so that is apples
    and oranges there. Except the later Linux Xandros versions which does
    use drive letters, oddly enough.
    BillW50, Aug 12, 2009
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  2. Deodiaus

    S.Lewis Guest

    cross-posting breeds such nice visitors.
    S.Lewis, Aug 12, 2009
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  3. Deodiaus

    BillW50 Guest

    In RnR typed on Wed, 12 Aug 2009 11:57:25 -0500:
    Well I never met a human that could hold all of this information yet.
    BillW50, Aug 12, 2009
  4. When a new hard drive is shipped from the factory, it is totally
    (TOTALLY) Blank; every single sector on the drive is filled with 512
    bytes of whatever "fill value" that manufacturer uses.

    A drive will not be recognized by Windows until it has a valid MBR
    (Master Boot Record, recorded on the first sector of the drive). A
    totally blank drive doesn't have an MBR, of course, so it is not
    recognized. [Note that you can have a valid MBR and still have NO
    partitions defined.]

    When you connect such a drive, Windows offers to "initialize" the drive
    .... that is, it is offering to create a valid (still empty, but valid)
    MBR. If you decline, the drive won't be seen at all except by "Disk
    Management" under "Computer Management" under "Administrative Tools"
    (note, by default, "Administrative Tools" and everything under it is
    hidden and is invisible, but it can be unhidden by right clicking on the
    "Start" button, the selecting "properties", then "Customize". Some
    computer makers unhide it by default, others leave it hidden.).

    Even if the drive has a valid MBR, it may still have no partitions, at
    all, of any kind. It may also have partition types that are not
    recognized by the running version of Windows (Mac partitions, Linux
    partitions, even NTFS partitions while running under Windows 98).
    Those, also, will not be given a drive letter.
    Barry Watzman, Aug 12, 2009
  5. Open "Disk Management" (under "Computer Management", in "Administrative
    Tools" (which must be "unhidden"). Right click the partition you want
    to access, select "assign drive letter", pick a letter and it will be
    assigned (assuming that the partition type is one recognized by the
    version of the OS being run).

    Re: "I'm scared to think that anyone has installed XP on a disk small
    enough to use FAT16!"

    That would be 2GB or less. That's tight for XP, and probably impossible
    for an updated version.
    Barry Watzman, Aug 12, 2009
  6. Deodiaus

    BillW50 Guest

    In Barry Watzman typed on Wed, 12 Aug 2009 14:45:41 -0400:
    Many drives comes pre-formatted with FAT. I am not sure why? Maybe to
    stop the high number of returns that there is nothing wrong with them
    except they were not partitioned and formatted by inexperienced Windows
    That is true for only the boot drive. Having a MBR on a non-boot drive
    is totally meaningless. It won't help or hurt anything as far as I know
    though. The BIOS determines which drive is the boot drive and it is
    selectable under many modern day BIOS.
    EFI partitions are often formatted as FAT (contains data) and often
    doesn't get a drive letter by Windows. So this is one example of an
    exception anyway.
    BillW50, Aug 12, 2009
  7. Deodiaus

    Ben Myers Guest


    That's exactly the way that I understand all this, contrary to the
    incoherent ramblings of another person responding to this thread. I
    made the mistake of thinking that said person actually had some pearls
    of wisdom and new insights. Apparently not... Ben Myers
    Ben Myers, Aug 12, 2009
  8. My experience is that it just writes an empty mbr without asking, if it
    doesn't find a valid signature (0xAA55 at offset 0x01FE) in the first

    I found this out when experimenting with logical volume management, and
    created a physical volume on a flash drive, using the entire device,
    instead of a partition on the device, meaning there was no mbr.

    I forgot to unplug the device before booting in windows. XP pro overwrote
    the first sector, with no warning or notification.

    Regards, Dave Hodgins
    David W. Hodgins, Aug 12, 2009
  9. The mbr contains the partition table.

    Regards, Dave Hodgins
    David W. Hodgins, Aug 12, 2009
  10. Deodiaus

    BillW50 Guest

    In David W. Hodgins typed on :
    Actually the first 446 bytes of a hard drive is the MBR itself, the next
    64 bytes contains the partition table. The two are not the same or
    BillW50, Aug 12, 2009
  11. The first 440 bytes contain the boot program (if any), followed by the
    disk signature, a couple of nuls, the primary partition table, and the
    mbr sig. They are all parts of the mbr.

    See or

    Regards, Dave Hodgins
    David W. Hodgins, Aug 12, 2009
  12. Deodiaus

    BillW50 Guest

    In David W. Hodgins typed on Wed, 12 Aug 2009 17:11:25 -0400:
    Well some combine the first 512 bytes of the drive and call it as the
    MBR. But only the first 446 bytes is actually part of the MBR, followed
    by 64 bytes for the partition table. But you can have no MBR code and
    still have a partition table. Data drives does this for example. You can
    install Windows on a data drive too, but some boot files must be on the
    boot partition drive. Windows XP for example, needs boot.ini, ntldr, and files there. The rest of Windows could be anywhere else as
    stated in the boot.ini file.

    You can prove what I am saying is true by taking a data drive (without
    any MBR or any attempts to make it bootable) and place it in position
    that the BIOS will try to boot it (data USB HDD or data flash drives
    works great for this test). And it will give you a message saying no OS
    is found (end of story).

    Add a MBR with FDisk /MBR (DOS), Fixmbr (Windows 2000/XP), or bootrec
    /FixMbr (Vista/Windows7) and the message will be totally different. As
    under Windows XP for example, will give you generally an error that
    ntldr (which generally means ntldr and/or is actually
    missing or hal.dll is missing, which generally means it can't find the
    rest of Windows (aka the Windows folder on so and so drive and
    partition) as stated in the boot.ini file.
    BillW50, Aug 12, 2009
  13. Re: "Many drives comes pre-formatted with FAT"

    I beg to differ. I don't believe that ANY hard drives come from a hard
    drive manufacturer with anything at all (not even an empty partition
    table). Note: I am talking about rotating platter mechanical hard
    drives, BARE DRIVES, coming directly from a drive mfgr. as bare drives.
    I am not talking about flash drives, or "enclosed" external USB drives.

    Re: "That is true for only the boot drive. Having a MBR on a non-boot
    drive is totally meaningless."

    You are simply wrong. The MBR is where the partition table resides. It
    is an absolute, no exceptions whatsoever requirement on EVERY drive,
    whether you boot from it or not. This is not debatable; you can't use a
    drive in a Windows system unless it has an MBR.

    EFI partitions are a very special case, they are not intended for user
    data storage and while they do create some "exceptions" to some of the
    general rules, I think that those are "technical exceptions" and don't
    change the essence of the discussion as it applies to the partitions
    that we [users] use for storing our operating systems and data on a
    routine, day-to-day basis.

    [I am presuming (and I think that everyone else is also) that we are
    talking about the classical MBR based system that has been in use since
    1982. Vista incorporates a totally different system for disk management
    that was just introduced with Vista and that is, at this time, not
    widely used, but I don't think that any of us were talking about that.]

    Barry Watzman, Aug 13, 2009
  14. Re: "My experience is that it just writes an empty mbr without asking"

    That is not my experience, but conceivably there are instances in which
    this might happen. In general, however, a "system" (whether talking
    about an OS or BIOS or whatever) should NEVER "just write" to a drive
    without asking. For reasons that, I think, are obvious. [The drive
    might be from some "foreign" system and might be present only for
    forensic investigation, and the one thing you do NOT want a system to do
    is "just write" on it without permission.]

    I note that you were dealing with a flash drive (USB presumably) and not
    a "hard drive" (a mechanical, rotating platter hard drive). Flash
    drives are not hard drives, and are not treated exactly the same way by
    the system in all regards.
    Barry Watzman, Aug 13, 2009
  15. Correct (the MBR contains the partition table); Bill does not know what
    he is talking about. There cannot be a partition, or a partition table,
    without an MBR.
    Barry Watzman, Aug 13, 2009
  16. Bill, you are making an ass of yourself.

    The MBR is the ENTIRE first sector of the hard drive and contains the
    MBR. Your insistence on defending your previous incorrect statement
    that an MBR was not necessary on a non-boot drive is just making you
    look foolish. When you are wrong, admit it.
    Barry Watzman, Aug 13, 2009
  17. This is really getting down to just semantics. All programs and
    documentation I've seen refer to the entire sector as the mbr,
    including the partition table, and the mbr signature in the last
    two bytes, following the partition table.

    While the mbr can contain the boot code, it also contains the volume
    signature, the primary partition table, and the mbr signature. The
    entire 512 byte sector is called the master boot record.

    I think we'll have to agree to disagree on this one.

    Regards, Dave Hodgins
    David W. Hodgins, Aug 13, 2009
  18. Agreed. I was quite annoyed when I viewed the device in hex and saw the
    first sector as all zeroes, except the 0x55aa in the last two bytes.
    Having had that experience with the usb flash drive, I haven't felt like
    testing a hard drive. When I have some time, I'll test that.

    Regards, Dave Hodgins
    David W. Hodgins, Aug 13, 2009
  19. Deodiaus

    BillW50 Guest

    In David W. Hodgins typed on Wed, 12 Aug 2009 19:49:47 -0400:
    I agree with everything you stated except calling the first 512 bytes as
    the MBR. I have no idea why some sites are calling the whole 512 bytes
    as the MBR. As I call the whole first 512 bytes as the boot sector.

    MBR + Partition Table = MBR?

    I don't think so. You really have to push fuzzy logic to make that work.

    MBR + Partition Table = Boot Sector?

    That make a lot more sense to me. <grin>
    BillW50, Aug 13, 2009
  20. Deodiaus

    Happy Oyster Guest

    Good link. This is what it says about the "signature":

    MBRs and disk identity

    Information contained in the Partition Table of an external hard drive as it
    appears in the utility program, QtParted, running under Linux.
    In addition to the bootstrap code and a partition table, master boot records may
    contain a Windows NT disk signature. This is a 32-bit
    value that is intended to uniquely identify the disk medium (as opposed to the
    disk unit â ” the two not necessarily being the same for
    removable hard disks).
    The disk signature was introduced by Windows NT version 3.5, but is now used by
    several operating systems, including the Linux
    kernel version 2.6 and later. Linux uses the NT disk signature at boot time to
    determine the location of the boot volume.[19]
    Windows NT (and later Microsoft operating systems) uses the disk signature as an
    index to all the partitions on any disk ever connected
    to the computer under that OS; these signatures are kept in Registry keys,
    primarily for storing the persistent mappings between disk
    partitions and drive letters. It may also be used in boot.ini files (though most
    do not), to describe the location of bootable Windows NT
    (or later) partitions.[20] One key (among many) where NT disk signatures appear
    in a Windows 2000/XP Registry is:
    If a disk's signature stored in the MBR was A8 E1 B9 D2 (in that order) and its
    first partition corresponded with logical drive C:
    under Windows, then the REG_BINARY data under the key value, \DosDevices\C:,
    would be:
    A8 E1 B9 D2 00 7E 00 00 00 00 00 00
    The first four bytes are said disk signature. (Note: In other keys, these bytes
    may appear in reverse order from that found in the MBR
    sector.) These are followed by eight more bytes, forming a 64-bit Integer, in
    little endian notation, which are used to locate the byte
    offset of this partition. In this case, 00 7E corresponds to the hexadecimal
    value 0x7E00 (32,256dec). Dividing this byte offset by
    512 (the size of a hard disk's physical sector in bytes) results in 63, which is
    the physical sector number (or LBA) containing the first
    block of the partition ([21]).
    If this disk had another partition with the values 00 F8 93 71 02 following the
    disk signature (under, e.g., the key value
    \DosDevices\D:), it would begin at byte offset 0x27193f800 (10,495,457,280dec),
    which is also the first byte of physical
    sector 20,498,940.

    M$ abuses the signature for its Nazi methods.

    That is the typical M$ hogwash.
    Happy Oyster, Aug 13, 2009
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