How would you describe Alex's "sound" overall?

Back in '97 I got in my car with a coworker. Test for Echo was in my CD player so it started playing, and my coworker said "Is this Rush?" I don't think he was aware they had a new album out; he may have just been a "casual" fan, but he was able to tell it was Rush just from Alex's guitar sound at the beginning of the title track.

With that in mind...what makes Alex's sound distinctive? Is it technique, technology, or a combination of the two?