DiskCheck is a developer tool used to verify Wii disc images. This is done by testing the disc image for integrity, saving a CRC of the disc, then verifying it. Two versions are available, v1.00 and v1.01; v1.00 does not have a banner, v1.01 does. v1.00 was created before the retail Wii System Menu was distributed to third party developers and was intended to be launched using Nmenu.

DiskCheck
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The channel banner, derived from a stock template included with the Wii SDK
GameID�DCK
Channel IOSIOS9

This software came bundled with Wii Menu Changer discs for developers, and was primarily used to verify a master image of a disc while testing it or prior to submitting it to Lotcheck.

Oddly enough, WAD installers install it straight to the NAND like a system application like the Mii Channel, Photo Channel, etc. Even a factory reset can't uninstall it, so Nmenu or other title deleters need to be used.

Gallery

A loop of DiskCheck's banner music by YouTube user thefluffydino
 
DiskCheck after checking RVL_UJI_DIAG