3DNow! is a set of instructions
which AMD added onto their
range of processors, starting
with the K6/II. In concept,
these are similar to Intel's
MMX instruction set, and is
in fact "backwards"-compatible with them.

3DNow! tailored programs generally
show a significant performance boost,
much more so than with "plain" MMX.
While MMX is used to do several integer
operations in parallel, 3DNow! adds
new floating point instructions
that can operate on 1 or 2 single-precision
floating point values at a time.
3DNow! supports addition, subtraction,
multiplication, division, negation,
absolute, comparison,
conversion to and from integers, and
square root. Division and square root
operators can also be limited to
12 bits precision for extra speed.