  We study the moduli space of the boundary conformal field theories describing
an unstable D-brane of type II string theory compactified on a circle of
critical radius. This moduli space has two branches, -- a three dimensional
branch S^3/Z_2 and a two dimensional branch described by a square torus T^2.
These two branches are joined along a circle. We compare this with the moduli
space of classical solutions of tachyon effective field theory compactified on
a circle of critical radius. This moduli space has a very similar structure to
that of the boundary conformal field theory with the only difference that the
S^3 of the S^3/Z_2 component becomes a deformed S^3. This provides one more
indication that the tachyon effective field theory captures qualitatively the
dynamics of the tachyon on an unstable D-brane.
