  We present the results from the RXTE observations of Cygnus X-1 in its high
state. In the energy range of 2-200 keV, the observed X-ray spectrum can be
described by a model consisting of a soft blackbody component and a broken
power-law with a high energy cutoff. The low energy spectrum (below about 11
keV) varies significantly from observation to observation while the high energy
portion changes little. The X-ray flux varies on all timescales down to
milliseconds. The power density spectrum (PDS) can be characterized by excess
red noise (``1/f'') at low frequencies and a white noise component that extends
to 1-3 Hz before being cut off. At higher frequencies, the PDS becomes
power-law again, with a slope of roughly -2 (i.e., ``1/f^2''). Broad peaks in
the range of 3-9 Hz are present, and might be due to quasi-periodic
oscillations. The PDS shows interesting spectral dependence: the 1/f component
becomes more prominent when the low-energy spectrum becomes softer. The
difference in the observed spectral and timing properties between the low and
high states is qualitatively consistent with a simple ``fluctuating corona''
model.
