Intel Extensible Firmware Interface - Manual (Page 403)

Protocols — Bootable Image Support
Version 1.10 12/01/02 11-43
ReadOnly TRUE if the media is marked read-only otherwise, FALSE . This
field shows the read-only status as of the most recent
WriteBlocks() call.
WriteCaching TRUE if the WriteBlocks() function caches write data.
BlockSize The intrinsic block size of the device. If the media changes, then
this field is updated.
IoAlign Supplies the alignment requirement for any buffer used in a data
transfer.
IoAlign values of 0 and 1 mean that the buffer can
be placed anywhere in memory. Otherwise, IoAlign must be
a power of 2, and the requirement is that the start address of a
buffer must be evenly divisible by
IoAlign with no remainder.
LastBlock The last logical block address on the device. If the media
changes, then this field is updated.
Description
The LogicalPartition is TRUE if the device handle is for a partition. For media that have
only one partition, the value will always be TRUE . For media that have multiple partitions, this
value is FALSE for the handle that accesses the entire device. The firmware is responsible for
adding device handles for each partition on such media.
The firmware is responsible for adding an EFI_DISK_IO interface to every EFI_BLOCK_IO
interface in the system. The EFI_DISK_IO interface allows byte-level access to devices.