We consider the problem of constructing reliable comparator networks built from unreliable comparators. In case of a faulty comparator inputs are directly output without comparison. A trivial lower bound of W(logn +k) on the depth of n-input k-fault tolerant sorting network is well known. We are interested in establishing exact lower bounds on the depth of such networks. To this end we consider fairly simple minimum-finding networks. Our main result is the first nontrivial lower bound on depths of networks computing minimum among n > 2 items in the presence of k > 0 faulty comparators. We prove that the depth of any such network is at least max(élogn u+ 2k, logn + klog[logn/( k+1)]). We also describe a network whose depth nearly matches the lower bound.
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