This exercise comes from the Pink Floyd song "Is There Anybody Out There?" from The Wall.  Most of the work is being done by the picking hand over an Am base chord.  The picking pattern only uses the top four strings of the guitar so it matches perfectly with your picking hand fingers.  David Gilmour uses a nylon string classical guitar to play this.  Nylon string guitars have slightly wider necks making fingerpicking a little easier.  You should be able to easily play this riff on an electric or steel string acoustic.

Practicing Tips

Since there is fret hand movement on the D or 4th string you'll want to fret so that the fingers playing the notes on the 2nd and 3rd strings don't need to reposition as the chord shape changes slightly.  That means you'll want to play the initial A minor chord with the 1st finger on the 2nd string, middle finger on the 3rd string and 3rd finger on the 4th string.  Then when the chord moves up to the 3rd and 4th fret on the 4th string you can simply slide up your 3rd finger or add your 4th finger without having to shift the others.