  Implications of the SL(2,R) symmetry of the c = 1 matrix models are explored.
Based on the work of de Alfaro, Fubini and Furlan, we note that when the Fermi
sea is drained, the matrix model for 2 dimensional string theory in the linear
dilaton background is equivalent to the matrix model of AdS_2 recently proposed
by Strominger, for which SL(2,R) is an isometry. Utilizing its Lie algebra, we
find that a topological property of AdS_2 is responsible for quantizing
D0-brane charges in type 0A theory. We also show that the matrix model
faithfully reflects the relation between the Poincare patch and global
coordinates of AdS_2.
