Volume Boot Sectors

Each DOS partition (also called a DOS volume) has its own volume boot sector. This is distinct from the master boot sector (or record) that controls the entire disk, but is similar in concept. Each volume boot sector contains the following:

• Disk Parameter Block: Also sometimes called the media parameter block, this is a data table that contains specific information about the volume, such as its specifications (size, number of sectors it contains, etc.), label name, etc.
• Volume Boot Code: This is code that is specific to the operating system that is using this volume and is used to start the load of the operating system. This code is called by the master boot code that is stored in the master boot record, but only for the primary partition that is set as active. For other partitions, this code sits unused.

The volume boot sector is created when you do a high-level format of a hard disk partition. The boot sector's code is executed directly when the disk is booted, making it a favorite target for virus writers.

Next: Active Partitions and Boot Managers