MBR
also: Master Boot Record, boot sector
The Master Boot Record is the first 512 bytes of a hard disk that contains the bootloader code and partition table, allowing the system to boot and identify disk partitions.
The Master Boot Record (MBR) occupies the first sector of a storage device and serves two critical functions: it holds the bootloader code that initializes the system, and it contains the partition table that defines how the disk is divided into partitions.
The MBR structure consists of 446 bytes of bootloader code, 64 bytes for the partition table (supporting up to 4 primary partitions), and 2 bytes for a boot signature (0xAA55). Each partition entry is 16 bytes and stores the partition's type, size, and location.
For example, on a typical Linux system, you might see MBR partitions using fdisk -l /dev/sda, which lists the partitions defined in the MBR. However, MBR has limitations: it only supports disks up to 2 TB and maxes out at 4 primary partitions, which is why modern systems often use GPT (GUID Partition Table) instead.