BasicLinearAlgebraCommunicationSubprograms (BLACS) is a library of communication subprograms written as an interface layer between ScaLapack and the communications programs MPI (MessagePassingInterface) and pvm (ParallelVirtualMachine). The idea was that ScaLapack programs could be written which would run unchanged with either MPI or pvm, when linked with the approporiate library.
BLACS is now incorporated into the current distributions of ScaLapack.