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This paper presents experimental evidences of the granular electron injection during channel hot-electron programming of NOR Flash memories. The statistical process ruling the discrete charge transfer from the substrate to the floating gate is shown to introduce a fundamental spread contribution to the programmed threshold-voltage distribution obtained by the staircase algorithm, determining its ultimate accuracy. However, the actual precision in the control of cell threshold-voltage during programming is shown to be quite far from this fundamental limitation due to random telegraph noise effects. Moreover, the scaling trend of the electron injection statistics and the random telegraph noise limitation to the accuracy of the programming algorithm shows that the latter will continue to represent the most severe constraint for the next nor technology nodes.