Favorites 498 129 Extended partitions

Basic Concepts

The so-called extended partition, strictly speaking it is not a meaningful partition, it is just a pointer to the next partition, this pointer structure will form a one-way list. So in the main boot sector in addition to the primary partition, only need to store a partition called extended partition data, through this extended partition of the data can find the next partition (in fact, the next logical disk) starting position, so that the starting position and so on to find all the partitions. Regardless of the number of logical disks established in the system, each logical disk can be found individually in the main boot sector through an extended partition parameter. [1]

The concept of extended partitioning is more complex, it is very easy to confuse the hard disk partition with the logical disk, the partition table of the fourth byte is the partition type value, the normal bootable more than 32MB basic DOS partition value is 06, the extended DOS partition value is 05. If you change the base DOS partition type to 05, you cannot start the system, and you cannot read and write the data.

If you change 06 to a DOS unrecognized type such as EFH, DOS considers the partition not to be a DOS partition and is certainly not readable or writable. Many people use this type of value to implement a single partition encryption technology, restore the original correct type value can make the partition return to normal. A hard disk primary partition has at least 1, a maximum of 4, and an extended partition can be no more than 1. and the primary partition + extended partition must not exceed 4 total. A logical partition can have several.

The primary partition that is activated under Windows is the boot partition of the hard disk, and he is the first partition of the hard disk, and the normal division is the C zone. Both the primary and logical partitions under Linux can be used to put the system on, booting the OS, and grub will be compatible with Windows system boot.

After dividing the main partition, the rest of the sections can be divided into extended partitions, which are generally divided into extended partitions, or not fully divided, and the remainder is wasted.

However, the extended partition is not used directly, and is used in logical partitioning, so the extended partition can be divided into logical partitions. Their relationship is a contained relationship, and all logical partitions are part of the extended partition.

In Linux, the first hard disk partition is HDA partition, the primary partition number is hda1-4, and the logical partition starts from 5.

Capacity of the hard disk = capacity of primary partition + capacity of extended partition

Capacity of the extended partition = The sum of the capacity of each logical partition

The primary partition can also become a "boot partition", which is identified by the operating system and the motherboard as the first partition of the hard disk. So the C-disk will always be in the first place on all partitions.

MBR (master boot Record) of the partition table (primary partition table) can only hold 4 partitions, if you want to divide more partitions will be an extended partition table (EBR), the extended partition table is placed on a system ID 0x05 primary partition, the primary partition is an extended partition, the extended partition can be divided into several partitions, Each partition is a logical partition.

2Partition Distinction

Both DOS and FAT file systems were originally designed to support up to 24 partitions on a single hard drive, using a 24 drive letter from C to Z, respectively. However, the partition table in the master boot record can only contain up to 4 partition records, in order to solve this problem effectively, DOS Partition command Fdisk allows the user to create an extended partition and then establish up to 23 logical partitions within the extended partition, each of which is assigned a separate drive letter. Can be used by the computer as a standalone physical device. Information about logical partitions is stored within the extended partition, and information about the primary and extended partitions is stored in the MBR of the hard disk. This means that no matter how many partitions a hard disk has, its master boot record contains only the primary partition (that is, the boot partition) and the extended partition two partitions.

Favorites 498 129 Extended partitions