We show that all supersymmetric Type IIA D-branes can be constructed as bound
states of a certain number of unstable non-supersymmetric Type IIA D9-branes.
This string-theoretical construction demonstrates that D-brane charges in Type
IIA theory on spacetime manifold X are classified by the higher K-theory
group K−1(X), as suggested recently by Witten. In particular, the system
of N D0-branes can be obtained, for any N, in terms of sixteen Type IIA
D9-branes. This suggests that the dynamics of Matrix theory is contained in the
physics of magnetic vortices on the worldvolume of sixteen unstable D9-branes,
described at low energies by a U(16) gauge theory.Comment: 32 pages (published version
