  In this paper, we consider the linear direct sum of a real normed linear
space with an order unit space and with a base normed space to obtain
respectively a new order unit space and a new base normed space. As a
consequence, we find that an $\ell_1$-space may be shown to be an order unit
space. (However, not in the natural order.) Dually, an $\ell_{\infty}$-space
may be shown to be a base normed space. To understand this aberration, we
characterize the real normed linear spaces which are isometrically isomorphic
to order unit spaces. We prove that other than the classical case of
$\ell_{\infty}$, $\ell_1$ is also isometrically isomorphic to an order unit
space whereas $\ell_2$ is not isometrically isomorphic to any order unit space.
