The lunatic fringe disagreed. In 1989, Danny Hillis boldly made a widely publicized bet with a leading computer expert that as early as 1995, more bits per month would be processed by parallel machines than by serial machines. He is looking right. As serial computers audibly groaned under the burden of pushing complex jobs through the tiny funnel of von Neumann's serial processor, a change in expert opinion suddenly swept through the computer industry. But parallel computers remain hard to manage.
Parallel software is a tangled web of horizontal, simultaneous causes.
You can't check such nonlinearity for flaws since it's all hidden corners. There is no narrative to step through. The code has the integrity of a water balloon, yielding in one spot as another bulges. Parallel computers can easily be built but can't be easily programmed. Parallel computers embody the challenge of all distributed swarm systems, including phone networks, military systems, the planetary 24-hour financial web, and large computer networks.