源代码中的解释：[platform_build/tools/releasetools/ota_from_target_files]
# Recovery is generated as a patch using both the boot image
# (which contains the same linux kernel as recovery) and the file
# /system/etc/recovery-resource.dat (which contains all the images
# used in the recovery UI) as sources. This lets us minimize the
# size of the patch, which must be included in every OTA package.
#
# For older builds where recovery-resource.dat is not present, we
# use only the boot image as the source.
这个文件比recovery.img明显要小，从这一段描述中可以看出，这里只是装载了recovery的资源，而没有kernel。