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The paper introduces the concept of two-dimensional optical storage (TwoDOS). In this concept, bits are written in a broad spiral consisting of a number of bit-rows stacked together in a hexagonal packing. Bits with a value '1' are represented physically as circular pit-holes on the disc, while bits with a value '0' are characterized by the absence of such a pit-hole. A scalar diffraction model is used to calculate the signal levels for various diameters of the pits. A stripe-wise Viterbi detector is proposed to perform 2D bit-detection with a limited state complexity of the trellis. Simulation results are shown for various diameters of the pits. A 2D modulation code is applied to eliminate patterns that yield a high probability of erroneous detection.