  Results of ASCA X-ray study of central regions of medium-richness clusters of
galaxies are summarized, emphasizing differences between cD and non-cD
clusters. The intra-cluster medium (ICM) is likely to consist of two (hot and
cool) phases within $\sim 100$ kpc of a cD galaxy, where the ICM metallicity is
also enhanced. In contrast, the ICM in non-cD clusters appears to be isothermal
with little metallicity gradient right to the center. The gravitational
potential exhibits a hierarchical nesting around cD galaxies, while a total
mass-density profile with a central cusp is indicated for a non-cD cluster
Abell~1060. The iron-mass-to-light ratio of the ICM decreases toward the center
in both types of clusters, although it is radially constant in peripheral
regions. The silicon-to-iron abundance ratio in the ICM increases with the
cluster richness, but remains close to the solar ratio around cD galaxies.
These overall results are interpreted without appealing to the popular
cooling-flow hypothesis. Instead, an emphasis is put on the halo-in-halo
structure formed around cD galaxies.
