  We study the symmetry structure of N=8 quantum mechanics, and apply it to the
physics of D0-brane probes in type I' string theory. We focus on the theory
with a global $Spin(8)$ R symmetry which arises upon dimensional reduction from
$2d$ field theory with $(0,8)$ supersymmetry. There are several puzzles
involving supersymmetry which we resolve. In particular, by taking into account
the gauge constraint and central charge we explain how the system preserves
supersymmetry despite having different numbers of bosonic and fermionic
variables. The resulting zero-point energy leads to a linear potential
consistent with supersymmetry, and the metric is largely unconstrained. We
discuss implications for type I' string theory and the matrix model proposal
for M theory.
