Partition Discovery; Nesting Of Legacy Mbr Partition Records - Intel Extensible Firmware Interface Specification

Extensible Firmware Interface Specification

16.2 Partition Discovery

EFI requires the firmware to be able to parse legacy master boot records, the new GUID Partition
Table (GPT), and El Torito logical device volumes. The EFI firmware produces a logical
device for each EFI Partition Entry, El Torito logical device volume, and if no EFI
BLOCK_IO
Partition Table is present any partitions found in the partition tables. Logical block address zero of
the device will correspond to the first logical block of the partition. See Figure 16-1.
BLOCK_IO
DISK
Pointers to partitions
Partition Table
The following is the order in which a block device must be scanned to determine if it contains
partitions. When a check for a valid partitioning scheme succeeds, the search terminates.
1. Check for GUID Partition Table Headers.
2. Follow ISO-9660 specification to search for ISO-9660 volume structures on the magic LBA.
 Check for an "El Torito" volume extension and follow the "El Torito" CD-ROM
specification.
3. If none of the above, check LBA 0 for a legacy MBR partition table.
4. No partition found on device.
308
Partition
Figure 16-1. Nesting of Legacy MBR Partition Records
12/12/00
BLOCK_IO
H dl
Partition
Partition
Pointers to partitions
Partition Table
Partition
Version 1.02