1. A method of executing Multiple Instructions Multiple Data (‘MIMD’) programs on a Single Instruction Multiple Data (‘SIMD’) machine, the SIMD machine comprising a plurality of compute nodes, each compute node capable of executing only a single thread of execution, the compute nodes initially configured exclusively for SIMD operations, the SIMD machine further comprising a data communications network, the network comprising synchronous data communications links among the compute nodes, the network characterized by a network topology, the method comprising: establishing on the SIMD machine a plurality of SIMD partitions, each SIMD partition comprising a plurality of the compute nodes, the compute nodes in each SIMD partition electronically isolated from compute nodes in other partitions of the SIMD machine and coupled to one another through links of the network for synchronous data communications for parallel SIMD operations among the compute nodes in each SIMD partition; booting in MIMD mode a first SIMD partition and a second SIMD partition; executing, by launcher programs on the compute nodes of the first SIMD partition booted in MIMD mode, a plurality of MIMD programs on two or more of the compute nodes of the first SIMD partition booted in MIMD mode, including replacing the launcher programs with the MIMD programs in process address space in computer memory of the two or more compute nodes, each MIMD program autonomously executing different instructions on different data; re-executing a launcher program by an operating system on a compute node in the first SIMD partition booted in MIMD mode upon termination of the MIMD program executed by the launcher program; determining by a scheduler that the first SIMD partition booted in MIMD mode is required, according to the network topology, to establish a new SIMD partition large enough to run a SIMD program that is scheduled for execution; moving by the scheduler data processing operations from the first SIMD partition booted in MIMD mode to the second SIMD partition booted in MIMD mode; and establishing by the scheduler the new SIMD partition large enough to run the SIMD program that is scheduled for execution, the new SIMD partition including compute nodes from the first SIMD partition booted in MIMD mode.