Master Boot Record

Tags

comp-arch

Is the first 512 bytes (beginning from physical offset 0) of a storage device, preceding the first disk partition.

The master boot record stores the storage-devices partition table and can use its first 440 bytes to contain an OS boot-loader. The MBR scheme limits the size of a partition entry to 32-bits meaning the maximum addressable storage space of a partitioned disk, using the MBR system and assuming 512-byte sectors, is 2-TiB (\( 2^{32} \times 512 \text{bytes} \)). MBR addresses blocks using LBA.

Warn: Some storage devices such as floppies or superfloppies lack MBRs whereas others can be configured to omit them entirely.

The MBR can contain one or more of:

• A partition table.
• Bootstrap code.
• Optional 32-bit disk timestamp.
• Optional 32-bit disk signature.

The bootstrap-code contains instructions to identify the configured bootable partition and then load and execute its volume boot record.