  We present the first SDO AIA observations of a global coronal EUV disturbance
(so-called "EIT wave") revealed in unprecedented detail. The disturbance
observed on 2010 April 8 exhibits two components: one diffuse pulse
superimposed on which are multiple sharp fronts that have slow and fast
components. The disturbance originates in front of erupting coronal loops and
some sharp fronts undergo accelerations, both effects implying that the
disturbance is driven by a CME. The diffuse pulse, propagating at a uniform
velocity of 204-238 km/s with very little angular dependence within its extent
in the south, maintains its coherence and stable profile for ~30 minutes. Its
arrival at increasing distances coincides with the onsets of loop expansions
and the slow sharp front. The fast sharp front overtakes the slow front,
producing multiple "ripples" and steepening the local pulse, and both fronts
propagate independently afterwards. This behavior resembles the nature of real
waves. Unexpectedly, the amplitude and FWHM of the diffuse pulse decrease
linearly with distance. A hybrid model, combining both wave and non-wave
components, can explain many, but not all, of the observations. Discoveries of
the two-component fronts and multiple ripples were made possible for the first
time thanks to AIA's high cadences (10-20 s) and high signal-to-noise ratio.
