Partition table

the partition table indicates the allocation of a non removable disk in partitions. Partitions are several independently usable parts of the non removable disk. Even if only one partition is furnished, a partition table is present in the master boat record.

Under most operating systems becomesit with the program fdisk furnished. There is also a multiplicity of further programs, in order to partitionieren a non removable disk.

On non removable disks according to standard the structure of the partition table described below is used. On storage media compatible to PC (z. B. Compact Flash maps, USB stick, Zip disk is this kind of Partitionierung possible, but not necessary. On storage media of other systems (z. B. Unix of systems, Mac OS etc.) is used other partition tables, which are not described here.

structure of the partition table

Offset *0 *1 *2 *3 *4 *5 *6 *7 *8 *9 *A *B *C *D *E *F
0000 eb 48 90 10 8e d0 UC 00 b0 b8 00 00 8e d8 8e c0
0010 fb 00 7c BF 00 06 b9 00 02 f3 a4 I/O 21 06 00
0190 61 64 00 20 45 72 72 6f 72 00 bb 01 00 b4 0e CD
01a0 10 AC 3c 00 75 f4 c3 00 00 00 00 00 00 00 00 00
01b0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 01
01c0 01 00 83 fe FF FF 3f 00 00 00 41 29 54 02 00 fe
01d0 FF FF 82 fe FF FF 80 29 54 02 companies e7 1d 00 00 fe
01e0 FF FF 83 fe FF FF 7a 11 72 02 companies e7 1d 00 00 fe
01f0 FF FF 05 fe FF FF 74 f9 8f 02 0c 83 6c 04 55 aa

as down described, gives it primary and extended partition tables. Their structure is identical. The table is at byte 446 (1BE hex) of the respective sector and has maximally 4 entriesà 16 bytes, it thus 64 byte is large. Afterwards to it follows the Magic NUMBER, which consists AA of the two bytes 55 hex and hex in the last two bytes of the sector. These become of Little Endian - CCUsas 16-Bit-Zahl AA55 hex interprets.

The accompanying table illustrates the situation of the partition table. The four partition entries are coloured emphasized. Yellow, green, cyanogen and the entries for the four primary partitions are blue. The signature is red deposited.


Such an entryis arranged as follows:

Storage location address
(in hexadecimals)
size of
(byte)
contents of
0x00 1 certainly whether partition be started can or not
(80 hex =bootfähig, 00 hex =nicht boatable)
0x01 3 CHS entry of the first sector
0x04 1 type of the partition (file system/type of partition)
0x05 3 CHS entry of the last sector
0x08 4 starting sector (relative to to the beginning of the non removable disk, or extended partition tables)
0x0C 4 number of sectors in the partition.

Unused entries are filled with zeros.

The CHS entries are coded as follows:

Format des CHS-Eintrages

Theremodern non removable disks the addressing by CHS (255 Heads × 63 sectors × 1023 cylinders × 512 bytes = approx. 8 give) is not sufficient, starting from this size always 255, 63 and 1023 for the CHS values one indicates and position andSize are then specified exclusively by the sector data. Thus also the maximum size of 2 TiB for a partition and 4 TiB for a non removable disk results. (2 32 -1 × 512 bytes = approx. 2 TiB)

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Stands important partition types with its

identification numbers the entry at offset 0x04 and. A. for:

Type byte (hex) file system
0x00 empty/unused
0x01 FAT12 (floppy disks)
0x04 FAT16 < Partition 0x06
FAT16 extended 32
MIB 0x05 > 32 MIB
0x07 HPFS (OS/2)or NTFS (Windows NT)
0x0B FAT32
0x0C FAT32 with bio sixth ion
0x0E FAT16 > Extended 32 MIB with
bio sixth ion 0x0F partition with bio sixth ion
0x12 EISA partition
0x42 of dynamic data media
0x82 Linux Swap
0x83 Linux native one
0xA5 FreeBSD
0xA6 OpenBSD
0xA9 NetBSD

primary ones + extended partition table

with one at the PC partitionierten medium the primary partition table before the signature at the end of sector 1 (master boat record) are put down. The partitions in the partition table of the MBR are called primary partitions. Only one partition in the MBR can be however also as extended (extended, type 5) marked. This refers then in the entry starting sector to the first extended part ion table.

This is in the first sector first extended partition. Each extendedPartition table defined exactly a logical partition and refers if necessary to the next extended partition. The extended partition tables function according to the principle of the concatenated list, therefore as many as desired logical partitions are possible behind the primary partitions. As length of theEntry the type 5 partition in the MBR is registered the sum of all concatenated extended partitions. Since a sector is always taken by the extended partition table, extended and logical partition can do not possibly equally large to be.

An extended partition table uses thus maximallythe two first entries of the partition table. The starting sectors are indicated here no longer relative to the beginning of the non removable disk:

  • The first entry describes the logical partition. Its starting sector is indicated always relative to the position of the current partition table.
  • The second entry can a concatenation to a further extended partition table contained and has always the type 5. In the starting sector of this entry always relative to the sector of the first extended partition table one refers.

Old operating systems always expect the start of a partition at the cylinder borders. Thereforea gap also today still results partition table extended by 63 sectors between and the starting sector of the appropriate logical partition in the case of common operating systems.

 

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