What is MBR disk?

MBR is short for Master Boot Record, MBR is also sometimes referred to as the master boot block, master partition boot sector, and sector 0. The MBR is the first sector of the computer hard drive that tells the computer how to load the operating system and how the hard drive is partitioned. MBR contains a small amount of executable code called the master boot code, the disk signature, and the partition table for the disk. When a storage device has been partitioned with the MBR partition scheme, the MBR contains the primary partition entries in its partition table

MBR disk only supports storage device no larger than 2 TB, so the MBR partition scheme is not recommended for disks larger than 2 TB, in this case, you should use GUID Partition Table (GPT). MBR disk also only supports up to four primary partitions. If you want more partitions, you have to create three primary partitions plus one extend partition, and then create logical partitions inside the extend partition.