I was goofing around last nite and put a riff into guitar pro that i made up while goofing around alt picking. This was all on the E string and ended with an E chord and repeats. All the notes fit on the E minor pent scale. Then moving up a string and playing the same thing and ending on an A chord. ACDC and many other bands do this moving riffs up from the E toA string. Would this be better considered changing key to A or accenting the A chord still in the key of E. Not really a big deal its basically a warm up exercise but i made me wonder this becuase i hear it in so many songs.
If I've understood what you've said correctly then you aren't changing the key of the riff when moving onto the A string as A is in the scale of E (I think).

If it was in the key of A you'd move it up to the D string to get the same chord progression in that particular key.

I think its the first two steps in the I-IV-V i.e. In the key of you've got: E - A - B and in the key of A you've got: A - D - E.

Hope this helps.
I think it's a run up and down the E string using all the notes in the E minor scale finishing on a full Em chord then moving the exact same pattern using the exact same frets but on the A string. So you would be playing the entire run up and down the A string using all the notes in the A minor scale and finishing with a full Am chord.
I suppose it is a key change,...or is it?
Yea thanks you both seem to get what im saying^ I think tonite I will play around with the idea that the riff is in the key of E with E (I) then A( IV)and ill make up a third line based on the B or B7 (V or V7) Chord and maybe make it into a bluesy rock progression. Well its an idea to mess around with at least. Again this was just farting around but it sounded cool.
The A string riff would have some out of key notes but thats fine. Thanks for the thoughts.
yeah it's definitely a key change. i like when it's used, it mixes things up nicely.

My mind is going. I can feel it.