A Hard Disk Drive could be N number of partitions that are logically independent. A partition is a single division of a HDD which is logically independent. The Partitions are addressed by using the Partition tables. A partition table is a 64-byte data structure that provides basic information for a computer’s operating system about the division of the hard disk drive (HDD) into primary partitions. The partition table is part of the master boot record (MBR), which is a small program that is executed when a computer boots in order to find the operating system and load it into memory.
There are two ways to store the partition table
1→ Master Boot Record (MBR)
2→ GUID Partition Table (GPT)
Let us have a brief overview on how the two partition methods are working.
Master Boot Record (MBR)
The master boot record (MBR) is a structure that holds the boot loader program and the partition table. The MBR is always located at the very start of the disk, at LBA 0 or 0,0,1 in CHS addressing where in LBA denotes Logical Block Addressing and CHS denotes Cylinder/Head/Sector. The role of the MBR is to find the active partition table and load its boot sector and execute it. MBR has the limitation as the disk cannot exceed 2 TB in Size.
The length of the MBR structure is 512 bytes which will be as follows
Boot Loader – 446 Bytes
Partition Table – 64 Bytes
Signature – 2 Bytes
The MBR partition could have maximum of 4 primary partitions or 3 primary partitions and an Extended or Logical Partitions.
Extended Boot Record (EBR)
If the MBR entry contains an Extended partition then it is possible to create multiple logical partitions and obviously there will be a boot record called Extended Boot Record to boot the extended partitions. Unlike the MBR, the EBR can be anywhere in the disks. The primary partitions are described under single partition table and so it’s limited in number. But the EBR contains Partition table for each logical partition and each EBR precedes the logical partition it describes. The first EBR will always be located on the very first sector of the extended partition. If another logical partition is created then the first EBR will be having an entry that point to the new EBR and thus multiple EBR’s form the chain from first to last.
GUID Partition Table (GPT)
The GUID partition Table is designed to succeed the legacy MBR partitions and to overcome its limitations. Unlike the MBR, in GPT, a number of 128 partition could be created. The GPT uses GUID to identify the partition types to avoid collisions. It provides a unique disk and partitions GUID’s for each partition. The GPT has another advantage of keeping the partition table and backup header at the end of the disk which could be used in case of failure of base one.
GPT uses CRC32 checksum algorithm to detect the error or corruption in the partition table. The CRC32 is an error detecting code which is used in storage devices to detect the accidental changes on raw data. Due to CRC the GPT provides greater reliability.
The GPT format is as follows
First 512 bytes of a disk – Same as MBR
Next 512 bytes of a disk – Primary GPT Header
16 KB following the second 512 bytes – Primary GPT table
16 KB before the last sector of disk – Secondary GPT table
Last 512 bytes of a disk – Secondary GPT Header
Vembu Image Backup has the ability to backup both the legacy MBR and New generation GPT partition disks with the RPO and RTO of 15 mins. You can get the Vembu Image Backup installer by initiating the request through our live chat in our website or through 24/7 support.
Interested in trying Vembu BDR suite?, Try Now on a 30-days free trial: https://www.bdrsuite.com/try/
Got questions? Email us at: vembu-support@vembu.com for answers.
Follow our Twitter and Facebook feeds for new releases, updates, insightful posts and more.
