Disk Sectors Critical to Startup

[Ice Czar]

Disk Sectors Critical to Startup


A sector is a unit of storage on a hard disk and is typically 512 bytes. Computers access certain sectors on a hard disk during startup to determine which operating system to start and where the partitions are located. The data stored on these sectors varies depending on the computer platform.

Computers that are x86-based begin the startup process from disks that contain a master boot record and are referred to as MBR disks. Itanium-based computers start up from disks that contain a GUID partition table and are referred to as GPT disks. MBR and GPT disks each have disk sectors critical to startup, but the differences in the sectors are not visible in the graphical user interface. Instead, you must use a disk-editing tool, such as DiskProbe, to see how the data on these sectors is structured. For more information about using DiskProbe, see "DiskProbe" earlier in this chapter.

Caution

* The ability to edit and repair these sectors on a byte-by-byte basis after corruption has occurred is invaluable, but using a disk-editing tool requires a thorough understanding of how data is organized on the sectors. If you make a mistake, you can damage or permanently overwrite critical on-disk data structures that might make all data on a disk or volume permanently inaccessible. Therefore, it is a good idea to use the information in this chapter to learn about the sectors used for startup, and then to examine the sectors on your own disks to further your learning.

Master Boot Record on Basic Disks
Boot Sectors on MBR Disks


Master Boot Record on Dynamic Disks

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Computer Boot Sequence
Inside the Boot Process Part 1 (NTFS) & Part 2 @ Windows & .NET Magazine
Troubleshooting Disks and Filesystems