Partition Manager Software

Partition Magic - Partition Manager Software

Extend partition with one step
Resize/Move partition without data loss.
Create, delete and format partion with simple steps. Copy partition and disk to transfer data with ease. Support disk and partition size larger than 2 TB. Keep your data safe even in case of power outages or hardware failure.

Understanding the 2 GB Boot Code Boundary

An operating system's boot code is stored in both the master boot record (MBR) and the partition boot record, enabling the OS to boot properly. In some operating systems, however, this boot code is written is such a way that it inadvertently imposes a limit on the location of both the partition boot record and the files needed to boot the OS.

DOS (versions 6.x and earlier) and Windows NT (versions 4.0 and earlier) are both affected by this boot code limitation. When booting these two operating systems, the cylinder-head-sector (CHS) address of the beginning boot code sector must be calculated in order to retrieve the sector's information and load and execute the next part of the boot process. The CHS value for the needed sector is calculated as follows:

Sector Number / Sectors Per Track
Because of the way the boot code is written, the product of this calculation must fit in a 16-bit register. The largest value a 16-bit register can contain is 64K. If the number is larger than 64K, the number is truncated, resulting in an incorrect value that skews the remaining calculations. The boot process fails to load and execute the needed sector, thus preventing the OS from booting.

Most current hard disks have 63 sectors per track, creating a 64K boot code boundary at 2 GB. If your disk is older and/or uses drive overlay software, this boundary may be lower.

If a partition begins or extends beyond this boundary, the CHS value of the partition's boot code sector cannot be correctly calculated; therefore, the partition and its OS cannot boot.

This same limit applies to the DOS IO.SYS file and the Windows NT file, NTLOADER.EXE. If either of these files are installed or moved beyond the 64K boot code boundary, the corresponding OS fails to boot. To boot properly, DOS requires that the first three sectors of IO.SYS be below the 2 GB boot code boundary.

Both the IO.SYS and NTLOADER.EXE files are usually located near the beginning of the partition in which they are installed. When you resize partitions using PartitionMagic, this area of the partition may be vacated to make room for a larger FAT or other file system structures. As a result, IO.SYS or NTLOADER.EXE may be moved beyond the 2 GB boundary, thus preventing the OS from booting.

The disk map in the PartitionMagic main window displays an arrow indicator at the 2 GB boot boundary, so you can see where your partitions are located.