We describe the parallelisation of the \gmresc\ method and its
implementation on distributed-memory architectures, using both networks
of transputers and networks of workstations under the PVM
message-passing system.  The test systems of linear equations
considered are those derived from five-point finite-difference
discretisations of partial differential equations.

A theoretical model of the computation and communication phases is
presented which allows us to decide for which values of the parameter
$c$ our implementation executes efficiently.  The results show that for
reasonably large discretisation grids the implementations are effective
on a large number of processors.