In this work we quantify the impact of dots size and dots number fluctuations on the programming window dispersion of multi-nanocrystal memory devices. Concerning dots size distribution, experimental imaging (i.e. transmission electron microscopy) is used and generalized assumptions are made, according to well known theoretical distributions. Concerning dots number distribution, a Poisson dispersion is assumed. Both a Monte Carlo simulation and a deep theoretical analysis (i.e. compound distributions theory) are exploited to assess in two different ways the overall results. Eventually clear guidelines, concerning dot density and dot distribution requirements, are provided for future memory generations. (C) 2003 Elsevier Ltd. All rights reserved.