Partition Table

Partition table is part of the master boot record, which is a small program that is executed when a PC starts up in order to locate Operating System and load it into RAM memory. In partitions, there are two types such as primary partition and extended partition. The information about these partition types is stored in a partition table. Each Partition table entry is 16 bytes long and maximum four entries will be available. Each entry starts at a prearranged offset from the start of the sector, as follows:

  • Partition 1 0x01BE (446)
  • Partition 2 0x01CE (462)
  • Partition 3 0x01DE (478)
  • Partition 4 0x01EE (494)

In partition table, Boot Indicator Field is used to detect whether the volume is the system partition or not. This field set we see in disk, which is having primary partitions on x-86-based computers. It is possible to have different file system and different operating system on different volumes of x86-based computers. For example, a PC might have MS-DOS on the first partition and Windows 7, Windows 8, UNIX on remaining partitions. We can set a primary partition by setting the boot indicator field on that partition table. While formatting partitions and logical drives, System ID Field describes which file system to be used to format it.

The total hard disk space is divided into four partitions or 3 partitions and one extended partitions. These partitions are determined by 16- byte entries that form the Partition table, which locates in master Boot record. In partition table entry, 1-byte code is used to identify partition type in hard disk. 0x05 and 0x0F codes are found in partition table entry which is used to find presence of extended partition.

Structure of a 16-byte partition Table Entry consists of

  • Boot Indicator
  • Starting Sectors in CHS value
  • Partition Type Descriptors
  • Ending Sectors in CHS values
  • Starting Sector
  • Partition Size

Partition types

Primary partition: A primary partition contains only one file system. In earlier DOS and Windows system first partition could be file system. However, Windows Operating System, which is came after Windows 95 prefer file system may contained in any partition.

Extended partition: A hard disk should contain only one extended partition later extended partitions can be divided into multiple logical partitions. In DOS or Windows systems, each logical partition can be recognized by assigning a letter.

One can easily alter, add, and delete existing partition dynamically in hard disk by using partition editor software. In hard disk, each partition is defined by start and end cylinder. When partition is deleted then its entry pointer is deleted from a table but data remains on disk until and unless being overwritten. In this situation, you need to use Remo Recover Windows tool to undelete partition along with all the files and folders stored in it.

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