A data disk was a method of information storage utilized by the Suliban Cabal.
In 2152, Captain Archer led a team to infiltrate a Suliban stealth-cruiser and retrieve three data disks which contained proof that the Cabal had framed Enterprise for the destruction of the Paraagan II mining colony. As the data disks were not compatible with Starfleet technology, the crew had to construct an interface in order to access the information. The crew initially had difficulty in doing so, until they realized that all three disks had to be used in unison. (ENT: "Shockwave")
Two years later, the Enterprise crew recovered a data disk from Silik which contained the schematics to a temporal conduit that the Na'kuhl were attempting to build on Earth, in 1944 of an alternate timeline. (ENT: "Storm Front, Part II")