The Fastest Computer Can Still Be Waiting for Data

Watch the gaps between calculations

Imagine a kitchen with exceptionally fast cooks and a pantry on another floor. Hiring more cooks helps only until everyone is waiting for ingredients. The same basic constraint appears in computing: processors need data, and transferring that data takes time and energy. A machine can have extraordinary arithmetic capability while an application spends a significant share of its time moving information.

Oak Ridge National Laboratory's Exascale Computing Project report identifies data movement through layered memory systems as a challenge for both performance and power consumption. It also describes the coordination needed between host processors and accelerators. These are central design concerns, not minor housekeeping details to be addressed after the scientific code is finished.