Intel Extensible Firmware Interface Specification page 206

Extensible Firmware Interface Specification
Description
The Simple File System protocol provides a minimal interface for file-type access to a device. This
protocol is only supported on some devices.
Devices that support the Simple File System protocol return an EFI_FILE_IO_INTERFACE.
The only function of this interface is to open a handle to the root directory of the file system on the
volume. Once opened, all accesses to the volume are performed through the volume's file handles,
using the
EFI_FILE
handles.
The firmware automatically creates handles for any block device that supports the following file
system formats:
•
FAT12, FAT16, FAT32
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protocol (see Section 10.2). The volume is closed by closing all the open file
12/12/00 Version 1.02