NKit/NKitFormat

The NKit Format is a non-lossy format for shrinking and restoring Wii and GameCube images. It supports clean / Redump images as well as scrubbed and hacked images. Some corrupt and bad images are supported too, although these quite often error.

There are 2 NKit output formats, raw (iso) and compressed (gcz). Both were designed with 1:1 preservation, size and playability in mind. Hardware support for Wii was sacrificed for smaller images. WBFS is currently the best available and Recoverable to Redump where not hacked or corrupt.

System	Format	Hardware Supported	Dolphin Supported	Restorable 1:1	Notes
GameCube	nkit.iso	Yes	Yes	Yes	Same as compacted GameCube iso
GameCube	nkit.gcz	No	Yes	Yes	GCZ is Dolphin's own block seekable compression format
Wii	nkit.iso	No (Dev Kit?)	Yes	Yes	RVT-H format only playable in Dolphin or a Dev Kit (Untested)
Wii	nkit.gcz	No	Yes	Yes	RVT-H in GCZ playable in Dolphin only

NKit Format images contain the bare minimum of data. All junk and scrubbing is removed. Non-uniform data is preserved in 256 byte blocks with a 4 byte header. Wii encryption and hashes are fully recreatable and removed. Meaning any remaining data is as compressible possible.

Header

NKit places its header at 0x200 in the Wii and GameCube disc headers.

Offset	Length	Name
0x200	0x4	NKit Header 'NKIT'
0x204	0x4	NKit Version ' v01'
0x208	0x4	Source image original CRC32
0x20C	0x4	NKit CRC - makes the NKit file CRC32 equal the source CRC at 0x208 (at 0x4 in GCZ)
0x210	0x4	Source image length
0x214	0x4	Forced Junk ID (When Disc ID differs - rare - GameCube only)
0x218	0x4	Wii Update partition CRC32 if removed when converting

NKit also modifies the Wii header to set the bytes at 0x60 and 0x61 to 0x1. This indicates to a Dev Kit and Dolphin that the encryption and hashes aren't present.

GameCube

The disc header (Boot.bin) length is 0x440. It's modified as detailed above. The other items remain untouched.

The filesystem and fst.bin are modified when converting to NKit.

Wii

The disc header length is 0x50000. The partition tables are modified to point to new partition offsets.

Removed Update Partition

The update partition may have been removed in order to save space. In this case offset 0x218 in the disc header will be the CRC32 of the removed partition. The removed partition will have been backed up in the 'Redump' recovery folder or in the 'NkitExtracted' recovery folder if it's not a known partition.

The original partition table is backed up at 0x50000. The next partition (Data or Channel) is located at 0x58000

Partitions

FileSystem

Both the GameCube and Wii use the same code to encode the filesystem. The only real difference is that Wii FST file offsets and lengths must be multiplied by 4 when mapping to files. The NKit Format uses a custom Run Length Encoding (RLE) to remove the gaps between files and shrink gaps to 4 bytes in most cases.