Servers provide services, e.g., instanciation of problems that a server can solve: for example, two services can provide the resolution of the same problem, one being sequential and the other parallel. A DIET task, also called a job, is created by the request of a client: it refers to the resolution of a service on a given server.
A service can be sequential or parallel, in which case its resolution
requires numerous processors of a parallel resource (a parallel
machine or a cluster of workstations). If parallel, the task can be
modeled with the MPI standard, or composed of multiple sequential
tasks (deployed for example with
ssh) resolving a single
service: it is often the case with data parallelism problems.
Note that when dealing with batch reservation systems, we will likely speak about jobs rather than about tasks.