Read-write and content-addressable holographic data storage

Recent progress made towards two variants of holographic data storage is summarized. For fast-access read-write systems, the extension of high density to high capacity using phase-conjugate readout, and signal processing to relieve alignment and distortion constraints are described. For content-addressable systems, massively parallel correlators and associated fidelity issues are discussed. The paper concludes with the prospects for the gated nonvolatile holographic storage media that both variants require.