In the section above, the message-passing paradigm was described as involving a set of sequential programs, one for each processor. In reality, it is rare for a parallel programmer to make full use of this generality and to write a different executable for each processor. The same operation is to be applied at every grid point.
Some vendors provide parallel environments which only support SPMD parallel programs.
In practice this is not usually a problem to the programmer, who can incorporate all the different types of process he or she requires into one overall executable.