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Partition question(extended partition)

By vlatko
Feb 9, 2006
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  1. yesterday i bought a new sata wd caviar 250gd hard disk and i want to partition it in one of 200gb and the other 50gb. so i booted of the windows xp cd, and first created the big partition 200gb and then created the small one 50gb using ntfs and installed windows on it. everything is fine but what bugs me is this. i installed powerquests partition magic 8 and my hard disk looks like this(i'm not home so i can't provide a screenshot)

    hard disk 250gb:
    local disk c:200gb - primary partition ntfs
    local disk d:50gb - logical partition ntfs
    extended partition - 50gb

    what i don't understand is the extended partition part. i never used partition before and i don't get how could there be another 50gb for that extended partiton? could someone explain this to me? and is it a problem that windows is on a logical partiton, not a primary? if windows should be on a primary partition, what can i do to make it one?

    thanks in advance. ;)
  2. lukeyu

    lukeyu TS Rookie Posts: 70

    ok, you must read "What is partition table!"

    What is Partition Table?

    Partition can be considered as a piece of disk space, which is marked thereby runs on some operating system. Partition table is located at the first sector (cylinder 0, head 0 and sector 1, MBR) of each hard disk. It memorizes information about sizes and locations of partitions on hard disk. The partition information is started on offset 1BEH of master boot sector. Each partition entry is 16 bytes long. The total partition table is 64 bytes long. Then partition table is limited to a maximum of 4 entries. That is, there is a maximum of 4 partitions, which is called primary partition and can be created on hard disk.

    But there are problems: many people want to create more than 4 partitions. So the extended partition is designed for this demand. Master extended partition is the primary partition. Differing from other partitions, the first sector of extended partition is not a boot sector, but another partition table, which is called logical partition table.

    Commonly, there are only two partition entries in logical partition table. One points to a partition, called logical partition, whose boundary must be limited to the extended partition. The other entry, if needed, of the extended partition table points to the next logical partition table. Similarly, its boundary is limited to its parents extended partition. And the next logical partition table may also have two partition entries: one points to a logical partition; the other points to another logical partition table and the rest may be deduced by analogy. Therefore, many partitions could be created in extended partition.

    Now let’s have a look at the layout of one partition entry.
    The 16 bytes of one entry are as follows:

    OFFSET BYTE DESCRIPTION
    0 1 Boot label. Tell computer to boot from this partition
    1 1 Starting head
    2 1 Lower 6 bits (bit 0 to bit 5) is starting sector.
    Higher 2 bits (bit 6 to bit 7) is the higher bits of starting cylinder
    3 1 The lower 8 bits of starting cylinder

    4 1 Partition type
    5 1 Ending head
    6 1 Lower 6 bits (bit 0 to bit 5) is ending sector.
    Higher 2 bits (bit 6 to bit 7) is the higher bits of ending cylinder
    7 1 The lower 8 bits of ending cylinder
    8 4 Leading sectors of this partition
    12 4 Number of sectors of this partition


    (a) Boot label (offset 0):
    Most of the disks have one primary partition. Some people want to have more operating systems on their computers, so they have to create some other primary partitions. To tell the computer from which operating system to boot, one "Active" partition is in need. That's why partition table always keeps an indicator of the currently "Active" partition - the one from which the computer boots. In Partition Table Doctor or Super Fdisk, the active partition is figured out by "Active" with "Yes".

    (b) Starting position (offset 1-3):
    Describes the partition's starting position, the cylinder, the head and the sector. Also called starting CHS.
    starting head = (OFFSET 1)
    starting sector = (OFFSET 2) & 0x3f
    starting cylinder = (((OFFSET 2) & 0xc0)<<2)|(OFFSET 3)

    (c) Partition type (offset 4):
    Indicates what file system is in the partition. For example, 06 or 0E indicates a FAT file system. 0B or 0C indicates a FAT32 file system. 07 indicates NTFS or OS/2 HPFS file system.

    (d) Ending position (offset 5-7):
    Describes the partition's ending position, the cylinder, the head and the sector. Also called ending CHS.

    (e) Leading sectors (offset 8-11):
    The number of sectors before this partition. If we count all sectors on hard disk in sequence from zero, this field will exactly point to the first sector of this partition.

    (f) Number of sectors (offset 12-15):
    The total number of sectors on this partition. So the size of this partition will be (Number of sectors)*512/1048576 MB.
  3. vlatko

    vlatko TS Rookie Topic Starter Posts: 30

    thnx for the reply, i read the article 2 times, and that's some serious complicated stuff for someone new to this, as i am, and for someone who knows just basic english. :)

    i could change my question, all i want is this, 2 partitions, one of 200gb for music, video and stuff and the other of 50gb for windows. how do i do that? i mean i did it but was it right? or should i do it again, and how? should i first create the small partition for windows and then the big one? should windows be on a primary partition? in other words, is that extended partition a must?
  4. Nodsu

    Nodsu TS Rookie Posts: 9,431

    You did it right.

    What happened, was the Windows default way of doing things. You can delete the logical+extended partition and create another primary one (using Partition Magic) and it will work just fine too.
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