1. An asymmetric data processing system comprising: a first group of one or more host computers, each comprising a memory, a network interface and one or more Central Processing Units (CPUs), each host computer accepting and responding to requests to process data; a second group of two or more Job Processing Units (JPUs), operating autonomously and asynchronously from one another, each JPU comprising a memory, a network interface, a data interface with exclusive access to one or more sources of data, and one or more general purpose CPUs, each JPU in the second group being responsive to requests received from a host computer to execute jobs and return results independent of execution at other JPUs, the jobs containing instructions for the processing of a particular subset of data under the JPU's exclusive control; and a network connecting the network interfaces within each group and between the two groups; wherein the sources of data comprise one or more storage devices which are directly accessed by no other JPU in the second group and by none of the host computers in first group.