  We have performed a uniform analysis of 79 clusters of galaxies with the
ROSAT HRI and ASCA to study the X-ray structure and evolution of clusters in
the redshift range 0.1 < z < 1. We determined the average X-ray temperatures
and the bolometric luminosities with ASCA and the spatial distributions of the
X-ray brightness with the ROSAT HRI by utilizing the isothermal beta-model. We
do not find any significant redshift dependence in the X-ray parameters
including the temperature, beta-model parameters, and the central electron
density. Among the parameters, the core radius shows the largest
cluster-to-cluster dispersions. We discovered that the histogram of the core
radius shows two peaks at 60 and 220 kpc. If we divide the cluster samples into
two subgroups corresponding to the two peaks in the core radius distribution,
they show differences in the X-ray and optical morphologies and in the X-ray
luminosity temperature relation. From these observational results, we suggest
that the clusters are divided into at least two subgroups according to the core
radius.
