MBR partition

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MBR Partition

The MBR (Master Boot Record) partitioning system goes back to the early days of PCs running DOS. It is often known as DOS MBR. Hard drives in those days were fairly small (250 MB was regarded as lavish), so only one sector could be spared for the bootloader and partition table. This first sector mostly contained bootloader code, with the small partition table located at the end.

Because of the small space available in the table, only four primary partitions could be accommodated. This became a problem as disk drives grew larger. The solution was to allow one (but only one) partition to be defined as an extended partition, a container for sub-partitions called "logical disks". There can be as many of these as the system administrator wants. They are listed in the first sector of the extended partition.

In Windows, there is a clear distinction between primary partitions and logical disks: Windows can only boot from a primary partition. Linux bootloaders such as GRUB and LILO do not make this distinction, so that the existence of two types of partition that behave identically in practice is clumsy and causes confusion. In addition, the small size of the partition table means that drives larger than 2 TB cannot be accommodated. Modern servers often have larger disks than that. For this reason, modern computers increasingly use GPT partition disks.