Under its SciDAC grants, the U.S. lattice gauge
theory community has created a unified program
environment that enables its members to achieve high
efficiency on terascale computers. Among the design
goals were to enable users to quickly adapt codes to
new architectures, easily develop new applications
and incorporate new algorithms, and preserve their
large investment in existing codes. These goals were
achieved through the development of the QCD
Applications Programming Interface (QCD API), which
is illustrated in the figure on the right.