5.2.13 What Did We Learn?

• The loosely synchronous programming model leads to programs that are easily developed, debugged, and modelled, and perform extremely well on parallel machines.

• Using high-level and collective communication routines simplifies coding for the user and allows implementors the flexibility to generate high performance on arbitrary architectures.

• A good parallel model of I/O and graphics leads to programs that are portable, efficient, and easily understood. They also adapt well to special-purpose hardware.

• You don't need a ``real operating system'' to get high performance from parallel computers. This is not surprising; a critical ``reality'' for generally useable systems is the ``ease of use'' and flexibility of ``real'' operating systems. They are not designed just for performance, and, indeed, sacrifice it for the other design features.

• Portability, programmability, and performance are the most important message-passing system qualities, and are not mutually exclusive.