  We analyze a sample of bright short bursts from the BATSE 4B-catalog and find
that many short bursts are highly variable ($\delta t_{min}/T\ll 1$, where
$\delta t_{min}$ is the shortest pulse duration and T is the burst duration).
This indicates that it is unlikely that short bursts are produced by external
shocks. We also analyze the available (first 1-2 seconds) high resolution (TTE)
data of some of the long bursts. We find that variability on a 10ms time-scale
is common in long bursts. This result shows that some long bursts are even more
variable than it was thought before ($\delta t_{min}/T\approx 10^{-4}-10^{-3}$
)
