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Knowledge Base > Products > BootIt Bare Metal > General Information > BootIt BM Overview for First-time Users

BootIt BM Overview for First-time Users

To help you understand BootIt Bare Metal, let’s start with a description of the partition table and how your system boot process normally works.

Note: This article provides details on standard MBR type disks. BootIt BM does not support being installed on GPT disks. 

The first sector (or block of data) on your hard drive is called the Master Boot Record (MBR). The MBR contains the partition table that defines the partitions (or areas) on your hard drive and a small program that transfers control to the first sector (boot sector) of one of the partitions.

The partition table can contain up to four primary partition entries that contain information on where the partition begins and ends, a flag to mark the active (or bootable) partition, and the type of file system used in the partition.

You can divide a special type of primary partition—an extended partition—into several smaller areas (or volumes). The volumes are contained entirely within the extended partition and they do not require extra space in the partition table.

Some point after the system starts, the BIOS reads in the MBR and transfers control to the program in the MBR. This program then looks for the active partition and, if found, loads the boot sector of that partition and transfers control to it.

Boot sectors are operating system and file system specific. The program located in this boot sector is responsible for starting the process that loads and executes the OS kernel.

Now that you know the basics of how the system normally boots, let’s focus on the Extended Master Boot Record (EMBR) and how it's used with BootIt BM.

The EMBR specification dynamically extends the capabilities of the system. It contains a block of code, called the EMBR Loader, and three tables—one for partition information, one for boot file information, and one for information on drivers that may need to be loaded on your system. Each of these tables can contain up to 255 entries.

The table in the EMBR that contains partition information is called the Master Partition Table (MPT). This table is used in place of the partition table to contain all partition information.

When an operating system is loading, at some point it looks for partitions in the partition table. At the very least it must find itself and typically assigns access to any of the other partitions or volumes that it recognizes.

BootIt BM handles the MPT and partition table by letting you create bootable configurations (or boot items) allowing you to choose which partitions from the MPT are to be placed into the partition table. If you are using the Limit Primaries setting, then all partitions from the MPT are automatically placed into the partition table. When the boot item is booted, the MBR partition table is updated to match the configuration of the boot item’s MBR Details.

You should now understand why, unless you’re using the Limit Primaries setting, you must not use any utilities that expand, move, or create a partition if it recognizes only the partitions in the partition table.

To get other partitions to show up in the operating system, you must assign the partitions to be loaded (up to four). Failure to correctly load the MBR Details section of the Boot Item is the most common cause of missing partitions.


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