  Typical persistent current ($I_{typ}$) in a mesoscopic normal metal ring with
disorder due to rough edges and random grain boundaries is calculated by a
scattering matrix method. In addition, resistance of a corresponding metallic
wire is obtained from the Landauer formula and the electron mean free path
($l$) is determined. If disorder is due to the rough edges, a ballistic
persistent current $I_{typ} \simeq e v_F/L$ is found to coexist with the
diffusive resistance ($ \propto L/l$), where $v_F$ is the Fermi velocity and $L
\gg l$ is the ring length. This ballistic current is due to a single electron
that moves almost in parallel with the rough edges and thus hits them rarely
(it is shown that this parallel motion exists in the ring geometry owing to the
Hartree-Fock interaction). Our finding agrees with a puzzling experimental
result $I_{typ}\simeq e v_F/L$, reported by Chandrasekhar et al. [Phys. Rev.
Lett. \textbf{67}, 3578 (1991)] for metallic rings of length $L \simeq 100 l$.
If disorder is due to the grain boundaries, our data reproduce theoretical
result $I_{typ}\simeq (e v_F/L) (l/L)$ that holds for the white-noise-like
disorder and has been observed in recent experiments. Thus, result
$I_{typ}\simeq e v_F/L$ in a disordered metallic ring of length $L \gg l$ is as
normal as result $I_{typ}\simeq (e v_F/L)(l/L)$. Which result is observed
depends on the nature of disorder. Experiments that would determine $I_{typ}$
and $l$ in correlation with the nature of disorder can be instructive.
