In this and the following paper, we provide an introduction to the Fujitsu VPP range of vector-parallel supercomputers and to some of the computational chemistry software available for the VPP. Here, we consider the hardware and the design of software to exploit its capabilities. The VPP employs proprietary vector processors connected via a crossbar switch in a distributed-memory architecture. High single-node performance requires consideration of vector operand lengths, arithmetic pipe utilization and memory-to-CPU bandwidth. Most parallel chemistry applications use either explicit `message-passing' or a `global-memory' paradigm, and benchmark results are presented for the communications performance of MPI, Linda and the Global Arrays.