(Master Boot Record disk) The original Windows method for dividing a disk into multiple partitions, each a maximum of 2.2TB. The MBR architecture is limited to four primary partitions or three primary and one extended partitions (see primary partition). From BIOS/MBR to UEFI/GPT The PC's BIOS firmware and MBR partition table were superseded by the UEFI firmware and GUID Partition Table (GPT). The GPT allows unlimited partitions as large as 18 exabytes each (Windows supports up to 128 partitions). In addition, there is only one instance of the MBR partition table, whereas the GPT creates a copy at the end of the partition. See master boot record, BIOS, UEFI and GPT.