A boot record, often referred to as a boot sector, is an umbrella term that describes a specific section of persistent data storage hardware. This generally includes hard disk drives (HDDs), solid-state drives (SSDs), floppy disks, and more.
Often positioned as the very first sector on the storage medium, this sector ranges in size from 512 to 4096 bytes. Although it's rather limited in capacity, the boot sector plays a vital role in the day-to-day usability of the hard drive or storage medium – particularly on IBM-based PCs.
What is a Master Boot Record?
The master boot record, or MBR, was introduced to the public alongside disk partitioning in 1983. First used with DOS 2.0, it's been a mainstay of IBM PC-compatible systems ever since.
Much like a generate boot record, the MBR stores critical data that is ultimately loaded into your system's RAM and executed via the BIOS. In the case of the MBR, this includes partition and file system data for each sector on your hard drive or storage medium. It also contains important executable code for the OS, which is typically known as a boot loader.
Unlike boot records, which are found on all mediums of IBM PC-compatible data storage, the MBR isn't seen on non-partitioned media. This includes floppy disks and other devices that are meant to mimic their functionality.
However, MBRs are limited to a maximum addressable storage space of 2 TiB (232 × 512 bytes) per partitioned disk. Note that this limit is measured in tebibytes – which use a binary system – as opposed to TB (terabytes), which are based on the power of 10.
As a result, the MBR framework is currently being phased out in favor of the GUID (globally unique identifier) Partition Table, or GPT.
What is a Volume Boot Record (VBR)?
Sometimes known as a volume boot sector, partition boot sector, or partition boot record, a VBR is another type of boot record for both partitioned and un-partitioned devices. Like a traditional boot sector, this includes HDDs, SDDs, floppy disks, and more.
When utilized on non-partitioned devices like floppy disks, the VBR comprises the first sector of the device's storage space. In this sense, it takes the place of the MBR. For partitioned devices, the VBR comprises the first sector of any single partition. This lets the MBR remain on the very first sector of the device as a whole.
What is an Extended Boot Record (EBR)?
Also known as an extended partition boot record, an EBR (or EPBR) represents a logical drive within an extended partition. It contains both an extended partition table and a signature word for the sector. If your system doesn't utilize an extended partition, then there are no logical drives associated with it and, as such, there isn't an EBR.
How Does a Boot Record Affect Data Integrity?
It's the boot record's job to store raw machine code for chainloading into the system's RAM before being executed by the BIOS. As one might expect, experiencing physical damage, data loss, or data corruption in your primary hard drive's boot record could render the entire system inoperable and inaccessible.
You may read more about disk partitioning in Wikipedia: Disk partitioning.