The task of converting large scale engineering programs to new computer architectures is expensive and nontrivial. An example of such a program is the structural analysis system SESAM. This paper describes the linear equation solver in the analysis part of SESAM. The algorithm is well suited for vector and parallel processing. The method uses substructure techniques at the highest level. Block sparsity is exploited at an intermediate level, while a new, sparse implementation of the extended BLAS routines forms the basis for the lowest level of the algorithm. Several problems unique to large scale general programs are described in relation to new computer technology.