  We have used ESO telescopes at La Silla and the Hubble Space Telescope (HST)
in order to obtain accurate B,V,I CCD photometry for the stars located within
200" (~= 2 half-mass radii, r_h = 1.71') from the center of the cluster NGC
6101. Color-Magnitude Diagrams extending from the red-giant tip to about 5
magnitudes below the main-sequence turnoff MSTO (V = 20.05 +- 0.05) have been
constructed.
  The following results have been obtained from the analysis of the CMDs: a)
The overall morphology of the main branches confirms previous results from the
literature, in particular the existence of a sizeable population of 73 "blue
stragglers", which had been already partly detected (27).They are considerably
more concentrated than either the subgiant branch or the main sequence stars,
and have the same spatial distribution as the horizontal branch stars (84%
prob. from K-S test). An hypothesis on the possible BSS progeny is also
presented. b) The HB is narrow and the bulk of stars is blue, as expected for a
typical metal-poor globular cluster. c) The derived magnitudes for the HB and
the MSTO, $V(ZAHB) = 16.59+-0.10, V(TO) = 20.05+-0.05, coupled with the values
E(B-V) = 0.1, [Fe/H] = -1.80, Y = 0.23 yield a distance modulus (m-M)_V = 16.23
and an age similar to other ``old'' metal-poor globular clusters. In
particular, from the comparison with theoretical isochrones, we derive for this
cluster an age of 13 Gyrs. d) By using the large statistical sample of Red
Giant Branch (RGB) stars, we detected with high accuracy the position of the
bump in the RGB luminosity function. This observational feature has been
compared with theoretical prescriptions, yielding a good agreement within the
current theoretical and observational uncertainties.
