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Thread: Hard Disk Problems Unallocated disk space @ the beginning

  1. #1

    Thumbs up Hard Disk Problems Unallocated disk space @ the beginning

    I wanna reinstall the OS but I just found that at the the beginning of the hard disk there's an unallocated disk space not allowing me to make any change with Partition magic, it just can be converted to a primary partition of 7,8 Mgs not allowing me to erase it nor merge it and off course i can't install the operating system again, how I could recover this space or at least move it from the root of the hard disk???

  2. #2
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    I would leave it alone. It is normal and doing no harm other than maybe looking a bit odd. You will always have some unallocated space like that when the first partition is an extended partition. Its because the mbr has to be on the first sector of the first cylinder and the extended partition must start on a cylinder boundary and it cant start on the mbr.

    Dont stick a tiny partition in there as it can throw out any boot.ini references.
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  3. #3
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    Quote Originally Posted by Paul Komski View Post
    You will always have some unallocated space like that when the first partition is an extended partition.
    Interesting, I didn't know that.
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  4. #4
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    7,8 megs? Whoop-tee-doo! No big deal, no great loss.

    But there is something wrong with this picture if what I am reading is correct.

    Are you using an installation of XP on an old 6.5 gig hard drive? Not that it won't fit or work, the problem is you are possibly sacrificing ah huge hit on performance utilizing such an old drive as this which is likely 5400RPM, 2meg cache when you have a much faster drive as your secondary that could be partitioned properly to give you a substantial gain in speed.

    Just what is 'Disk 2'?
    There's no place like 127.0.0.1

  5. #5
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    I didn't know that
    The maths is the give away.

    A "cylinder" usually consists of 255 heads of 63 sectors of 512 bytes.
    255 x 63 x 512 = 8225280 bytes
    8225280 / 1024 = 8032.5 kB (binary kilobytes or kibibytes)
    8032.5 / 1024 = 7.8 MB (binary megabytes or mebibytes)

    Each Logical partition begins with its own equivalent of the MBR known as an EPBR and it contains two partition table entries. The first EPBR partition table references the logical partition itself and the second one references the start of the next EPBR ... and so on until the last logical which only has one partition table entry referencing itself.

    An extended partition would like to have its first EPBR on sector 0 of course but that has been commandeered by the MBR and it thus needs a new home. Because it is conventional to start a partition on a cylinder boundary the next available cylinder boundary is usually 7.8 MB from the start of the drive. The first primary (non-extended) partition's boot sector and all the boot sectors in an extended partition start 63 sectors from the relevant boot record (MBR or EPBR). The next three primary partition boot sectors (if created) all start on the first sector of a new cylinder boundary and are referenced from the MBR.
    Last edited by Paul Komski; 05-26-2007 at 09:05 PM.
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  6. #6
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    Thanks Paul. That makes perfect sense.
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  7. #7
    I won't use that disk, I will use the other one, 80gbs I'll be using just this newer drive of course, I've tried to install winxp but didn't allow me to do so, because of disk problems, this little space doesn't let me make any change move it or merge it nor erase it, and the problem is that it is at the first sector of disk!!!

  8. #8
    Quote Originally Posted by Paul Komski View Post
    I would leave it alone. It is normal and doing no harm other than maybe looking a bit odd. You will always have some unallocated space like that when the first partition is an extended partition. Its because the mbr has to be on the first sector of the first cylinder and the extended partition must start on a cylinder boundary and it cant start on the mbr.

    Dont stick a tiny partition in there as it can throw out any boot.ini references.
    If I elliminate the extented partition, it will be erased that unallocated space??, 'cuz I need that disk for booting the OS, and I'm afraid that I need the first sector clean for installing WinXP

  9. #9
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    Backup any critical data before you begin.
    Delete D
    Resize F to 60,000 MB (and set the Free Space after the drive as 0).
    Resize the extended partiton to snugly fit round the F drive

    You should now have approx 10gig of space at the start of your big drive.

    You can now either simply copy C and paste it into that space or do a clean reinstall into the same area. If you go the clean install route then remove the smaller drive while you do this by booting to the installation CD.

    Finally ensure the BIOS or boot manager is set to boot the correct drive and partition and you may need to check that the new partition has been marked as the active partition. The tiny partition would be the C: drive and only hold a few boot files and the Windows partition would get another drive letter according to the rules on drive letter assignments under the NT-based OSes.

    PS
    For WinXP (SP1 or above) it doesnt really matter where the primary partition is as long as it is the active partition and that boot.ini in that partition has the correct boot partition and Windows directory references to match. It could quite happily be at the end of the drive.

    It is also possible to use one small primary partiton for booting from and choose a partition anywhere (including a logical partition) for the Windows Partition that you would boot to. Thus you could in fact create a tiny FAT partition in the area in front of the extended partition, mark it as active and then install from that partition to any other primary or logical partition with an appropriate file system.

    Many ways to skin cats.
    Last edited by Paul Komski; 05-27-2007 at 03:41 PM. Reason: PS
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